STEAM

UTIL

IZATIO

N

DESIGNOF FLUID

SYSTEMS

Published by

$19.95 per copy

Copyright © 2004by Spirax Sarco, Inc.

All Rights ReservedNo part of this publication may be reproduced, stored in a

retrieval system or transmitted, in any form or by any means,electronic, mechanical, photocopying, recording, or otherwise,

without the prior written permission of the publisher.

PREFACERecognizing the on-going need for education as it relates to the

fundamentals of steam including the most efficient use of its heat content, Spirax Sarco has developed the Steam Utilization Course.This handbook represents over 80 years of steam experience in the

proper selection, sizing and application of steam traps, pressure and temperature controls, and condensate recovery systems

in major industrial plants throughout the world.

The Steam Utilization Course can be used in conjunction with“Design of Fluid Systems—Hook Ups” for a complete and

concise knowledge of the use of steam for heat.

Spirax Sarco, Inc.1150 Northpoint Blvd.Blythewood, SC 26016

(803) 714-2000Fax: (803) 714-2222

2

3

Spirax Sarco

Spirax Sarco is the recognized industry standard forknowledge and products and for over 85 years hasbeen committed to servicing the steam users world-wide. The existing and potential applications for steam,water and air are virtually unlimited. Beginning withsteam generation, through distribution and utilizationand ultimately returning condensate to the boiler,Spirax Sarco has the solutions to optimize steam sys-tem performance and increase productivity to savevaluable time and money.

In today’s economy, corporations are looking for reli-able products and services to expedite processes andalleviate workers of problems which may arise withtheir steam systems. As support to industries aroundthe globe, Spirax Sarco offers decades of experience,knowledge, and expert advice to steam users world-wide on the proper control and conditioning of steamsystems.

Spirax Sarco draws upon its worldwide resources ofover 3500 people to bring complete and thorough ser-vice to steam users. This service is built into ourproducts as a performance guarantee. From initial con-sultation to effective solutions, our goal is tomanufacture safe, reliable products that improve pro-ductivity. With a quick, responsive team of salesengineers and a dedicated network of local authorizeddistributors Spirax Sarco provides quality service andsupport with fast, efficient delivery.

Reliable steam system components are at the heart ofSpirax Sarco’s commitment. Controls and regulatorsfor ideal temperature, pressure and flow control; steamtraps for efficient drainage of condensate for maximumheat transfer; flowmeters for precise measurement ofliquids; liquid drain traps for automatic and continuousdrain trap operation to boost system efficiency; rotaryfilters for increased productivity through proper filteringof fluids; condensate recovery pumps for effective con-densate management to save water and sewage costs;stainless steel specialty products for maintaining qual-ity and purity of steam; and a full range of pipelineauxiliaries, all work together to produce a productivesteam system. Spirax Sarco’s new line of engineeredequipment reduces installation costs with prefabricatedassemblies and fabricated modules for system integri-ty and turnkey advantages.

From large oil refineries and chemical plants to locallaundries, from horticulture to shipping, for hospitals,universities, offices and hotels, in business and gov-ernment, wherever steam, hot water and compressedair is generated and handled effectively and efficiently,Spirax Sarco is there with knowledge and experience.

For assistance with the installation or operation of anySpirax Sarco product or application, call toll free:

1-800-883-4411

Contents

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BASIC STEAM ENGINEERING PRINCIPLES 6

INTRODUCTION 6

WHAT IS STEAM 6

DEFINITIONS 6

THE FORMATION OF STEAM 6

Steam Saturation Table 8

STEAM GENERATION 10

BOILERS & BOILER EFFICIENCY 10

SELECTION OF WORKING PRESSURES 11

Steam Velocity 12

Air and Non-Condensable Gases 13

STEAM SYSTEM BASICS 14

STEAM PIPING DESIGN CONSIDERATIONS 15

STEAM AND CONDENSATE METERING 17

WHY MEASURE STEAM? 18

Plant Efficiency 18

Energy Efficiency 18

Process Control 18

Costing and Custody Transfer 18

CONTROL AND REGULATION OF STEAM 19

PRESSURE REDUCING VALVES 19

Direct Acting Valves 19

Pilot Operated Valves 20

Selection and Application 21

TEMPERATURE CONTROL VALVES 22

Manual Controls 22

Self-Acting Controls 22

Pilot Operated Controls 23

Pneumatic Controls 24

Proportional Control Bands 24

STEAM TRAPS AND THE REMOVAL OF CONDENSATE 26

CONDENSATE REMOVAL 26

Air Venting 27

Thermal Efficiency 27

Reliability 27

Contents

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STEAM TRAPS 27

Mechanical Steam Traps 28

Thermostatically or Temperature Controlled Traps 30

Thermodynamic Steam Traps 32

Variations on Steam Traps 33

STEAM TRAP TESTING METHODS 37

Visual Testing 37

Ultrasonic Trap Testing 37

Temperature Testing 37

Conductivity Testing 38

BY-PASSES AROUND STEAM TRAPS 39

PREVENTIVE MAINTENANCE PROGRAMS 39

Steam Trap Fault Finding 39

Steam Trap Discharge Characteristics 41

STEAM TRAP SELECTION 41

Waterlogging 41

Lifting of Condensate 42

REQUIREMENTS FOR STEAM TRAP/APPLICATIONS 42

Application Requirements 42

Steam Trap Selection Chart 43

Steam Trap Sizing 44

STEAM TRACING 45

CRITICAL TRACING 45

NON-CRITICAL TRACING 45

Attaching Tracer Lines 46

JACKETED PIPE TRACERS 47

STEAM TRACING MANIFOLDS 48

CONDENSATE MANIFOLDS 48

CONDENSATE MANAGEMENT 50

FLASH STEAM RECOVERY 51

CONDENSATE RECOVERY SYSTEMS 55

Electrically Driven Pumps 57

Non Electric Pressure Powered Pumps 58

WATERHAMMER IN CONDENSATE RETURN LINES 60

STEAM UTILIZATION COURSE REVIEW 62

Basic Steam Engineering Principals

6

IntroductionThis Spirax Sarco Steam

Utilization Course is intended tocover the basic fundamentals andefficient usage of steam as a costeffective conveyor of energy (Fig.2) to space heating or processheating equipment. The use ofsteam for power generation is aspecialized subject, already welldocumented, and is outside thescope of this course.

This course has beendesigned and written for thoseengaged in the design, operation,maintenance and or general careof a steam system. A moderateknowledge of physics isassumed. The first part of thiscourse attempts to define thebasic terminology and principlesinvolved in steam generation andsystem engineering.

What Is SteamLike many other substances,

water can exist in the form ofeither a solid, liquid, or gas. Wewill focus largely on liquid andgas phases and the changes thatoccur during the transitionbetween these two phases.Steam is the vaporized state ofwater which contains heat energyintended for transfer into a varietyof processes from air heating tovaporizing liquids in the refiningprocess.

Perhaps the first thing that weshould do is define some of thebasic terminology that will beused in this course.

DefinitionsBTU

The basic unit of measure-ment for all types of heat energyis the British Thermal Unit orBTU. Specifically, it is the amountof heat energy necessary to raiseone pound of water one degreeFahrenheit.

TemperatureA degree of hot or cold mesuredon a definite scale. For all practical purposes a measure-ment from a known starting pointto a known ending point.

HeatEnergy

SaturationThe point where a substance canhold no more energy withoutchanging phase (physical state).

EnthalpyThe term given for the total energy, measured in BTU’s, dueto both pressure and temperatureof a fluid or vapor, at any giventime or condition.

Gauge Pressure (PSIG)Pressure shown on a standardgauge and indicated the presureabove atmospheric pressure.

Absolute Pressure (PSIA)The pressure from and aboveperfect vacuum

Sensible Heat (hf) The heat energy that raises thewater temperature from 32°F. Themaximum amount of sensibleheat the water can absorb isdetermined by the pressure of theliquid. (Fig 1 & 2)

Latent Heat (hfg)The enthalpy of evaporation. Theheat input which produces achange of water from liquid togas.

Total HeatIs the sum of sensible heat andlatent heat (ht=hf+hhfg). (Fig 1)

The Formation of SteamSteam is created from the

boiling of water. As heat energy(BTU’s) is added to water, thetemperature rises accordingly.When water reaches its satura-tion point, it begins to changefrom a liquid to a gas. Let’s inves-tigate how this happens byplacing a thermometer in one

pound of water at a temperatureof 32˚F, which is the coldest tem-perature water can exist atatmospheric pressure beforechanging from liquid to a solid.

Let’s put this water into a panon top of our stove and turn onthe burner. Heat energy from theburner will be transferred throughthe pan into the water, causingthe water’s temperature to rise.

We can actually monitor theheat energy transfer (Fig.1) bywatching the thermometer levelrise - one BTU of heat energy willraise one pound of water by onedegree Fahrenheit. As eachdegree of temperature rise is reg-istered on the thermometer, wecan read that as the addition of 1BTU. Eventually, the water tem-perature will rise to its boilingpoint (saturation temperature) atatmospheric pressure, which is212°F at sea level. Any addition-al heat energy that we add at thispoint will cause the water to beginchanging state (phase) from a liq-uid to a gas (steam).

At atmospheric pressure andat sea level we have added 180BTU’s, changing the water tem-perature from 32°F to 212°F(212-32=180). This enthalpy isknown as Sensible Heat (BTUper pound). If we continue to addheat energy to the water via theburner, we will notice that thethermometer will not change, butthe water will begin to evaporateinto steam. The heat energy thatis being added which causes thewater’s change of phase from liq-uid to gas is known as LatentHeat. This latent heat content isthe sole purpose of generatingsteam. Latent heat (BTU perpound) has a very high heat con-tent that transfers to colderproducts/processes very rapidlywithout losing any temperature.As steam gives up its latent heat,it condenses and the water is the

Basic Steam Engineering Principals

7

same temperature of the steam.The sum of the two heat contents,sensible and latent, are known asthe Total Heat.

A very interesting thing hap-pens when we go through thisexercise and that is the change involume that the gas (steam)occupies versus the volume thatthe water occupied. One poundof water at atmospheric pressureoccupies only .016 cubic feet, butwhen we convert this water intosteam at the same pressure, thesteam occupies 26.8 cubic feetfor the same one pound.

The steam that we have justcreated on our stove at home willprovide humidification to the sur-rounding air space along withsome temperature rise. Steam isalso meant to be a flexible energycarrier to other types of process-es. In order to make steam flowfrom the generation point toanother point at which it will beutilized, there has to be a differ-ence in pressure.

Therefore, our pan typesteam generator will not createany significant force to move thesteam. A boiler, for all practicalpurposes, is a pan with a lid.There are many types of boilersthat are subjects of other cours-es. We will simply refer to themas boilers in this course. If wecontain the steam within a boiler,pressure will begin to rise with thechange of volume from liquid togas. As this pressure rises, theboiling point of the water insidealso rises. If the pressure of satu-rated steam is known, thetemperature is also known. Wewill consider this relationship laterwhen we look again at the satu-rated steam tables.

Another thing that happenswhen steam is created in a boileris that the gas (steam) is com-pressed into a smaller volume (ft3per pound). This is because the

non-compressible liquid (water) isnow a compressible gas. Thehigher the pressure, the higherthe temperature. The lower thelatent heat content of the steam,the smaller the volume the steamoccupies (Fig. 3). This allows theplant to generate steam at highpressures and distribute thatsteam in smaller piping to thepoint of usage in the plant. Thishigher pressure in the boiler pro-vides for more driving force tomake the steam flow.

The need for optimum efficiency increases with everyrise in fuel costs. Steam and con-densate systems must becarefully designed and main-tained to ensure thatunnecessary energy waste iskept at a minimum. For this rea-son, this course will deal with thepractical aspects of energy con-servation in steam systems, aswe go through the system.

Figure 1Steam Saturation Curve Graph at a Specific Boiler Pressure

Figure 2Steam Vs. Electricity

Temperature/Pressure

SensibleHeat

Latent Heat

Total Heat

25

20

15

10

5

0

Cost ($) per1,000,000BTU’ s ofEnergy

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Basic Steam Engineering Principals

8

Figure 3: Steam Saturation Table

Gauge Press.Absolute

TemperatureSensible Latent Total Spec. Volume

in Hg. Vac.Pressure

Degrees F(hf) (hfg) (hg) Steam (Vg)

psia BTU/LB BTU/lb BTU/lb ft3/lb

27.96 1 101.7 69.5 1032.9 1102.4 333.025.91 2 126.1 93.9 1019.7 1113.6 173.523.81 3 141.5 109.3 1011.3 1120.6 118.621.83 4 153.0 120.8 1004.9 1125.7 90.5219.79 5 162.3 130.1 999.7 1129.8 73.4217.75 6 170.1 137.8 995.4 1133.2 61.8915.7 7 176.9 144.6 991.5 1136.1 53.5713.66 8 182.9 150.7 987.9 1138.6 47.2611.62 9 188.3 156.2 984.7 1140.9 42.329.58 10 193.2 161.1 981.9 1143.0 38.377.54 11 197.8 165.7 979.2 1144.9 35.095.49 12 202.0 169.9 976.7 1146.6 32.353.45 13 205.9 173.9 974.3 1148.2 30.011.41 14 209.6 177.6 972.2 1149.8 28.0

Gauge Pressurepsig

0 14.7 212.0 180.2 970.6 1150.8 26.81 15.7 215.4 183.6 968.4 1152.0 25.22 16.7 218.5 186.8 966.4 1153.2 23.83 17.7 221.5 189.8 964.5 1154.3 22.54 18.7 224.5 192.7 962.6 1155.3 21.45 19.7 227.4 195.5 960.8 1156.3 20.46 20.7 230.0 198.1 959.2 1157.3 19.47 21.7 232.4 200.6 957.6 1158.2 18.68 22.7 234.8 203.1 956.0 1159.1 17.99 23.7 237.1 205.5 954.5 1160.0 17.210 24.7 239.4 207.9 952.9 1160.8 16.511 25.7 241.6 210.1 951.5 1161.6 15.912 26.7 243.7 212.3 950.1 1162.3 15.313 27.7 245.8 214.4 948.6 1163.0 14.814 28.7 247.9 216.4 947.3 1163.7 14.315 29.7 249.8 218.4 946.0 1164.4 13.916 30.7 251.7 220.3 944.8 1165.1 13.417 31.7 253.6 222.2 943.5 1165.7 1318 32.7 255.4 224.0 942.4 1166.4 12.719 33.7 257.2 225.8 941.2 1167.0 12.320 34.7 258.8 227.5 940.1 1167.6 1222 36.7 262.3 230.9 937.8 1168.7 11.424 38.7 265.3 234.2 935.8 1170.0 10.826 40.7 268.3 237.3 933.5 1170.8 10.328 42.7 271.4 240.2 931.6 1171.8 9.8730 44.7 274.0 243.0 929.7 1172.7 9.4632 46.7 276.7 245.9 927.6 1173.5 9.0834 48.7 279.4 248.5 925.8 1174.3 8.7336 50.7 281.9 251.1 924.0 1175.1 8.4038 52.7 284.4 253.7 922.1 1175.8 8.1140 54.7 286.7 256.1 920.4 1176.5 7.8342 56.7 289.0 258.5 918.6 1177.1 7.5744 58.7 291.3 260.8 917.0 1177.8 7.3346 60.7 293.5 263.0 915.4 1178.4 7.1048 62.7 205.6 265.2 913.8 1179.0 6.8950 64.7 297.7 267.4 912.2 1179.6 6.6852 66.7 299.7 269.4 901.7 1180.1 6.5054 68.7 301.7 271.5 909.2 1180.7 6.3256 70.7 303.6 273.5 907.8 1181.3 6.1658 72.7 305.5 275.3 906.5 1181.8 6.0060 74.7 307.4 277.1 905.3 1182.4 5.8462 76.7 309.2 279.0 904.0 1183.0 5.7064 78.7 310.9 280.9 902.6 1183.5 5.5666 80.7 312.7 282.8 901.2 1184.0 5.4368 82.7 314.3 284.5 900.0 1184.5 5.31

Basic Steam Engineering Principals

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Figure 3 (Cont.): Steam Saturation TableGauge Absolute

TemperatureSensible Latent Total Specific

Pressure PressureDegrees F

(hf) (hfg) (hg) Volumepsig psia BTU/LB BTU/lb BTU/lb Steam (Vg) ft3/lb

70 84.7 316.0 286.2 898.8 1185.0 5.1972 86.7 317.7 288.0 897.5 1185.5 5.0874 88.7 319.3 289.4 896.5 1185.9 4.9776 90.7 320.9 291.2 895.1 1185.9 4.8778 92.7 322.4 292.9 893.9 1186.8 4.7780 94.7 323.9 294.5 892.7 1187.2 4.6782 96.7 325.5 296.1 891.5 1187.6 4.5884 98.7 326.9 297.6 890.3 1187.9 4.4986 100.7 328.4 299.1 889.2 1188.3 4.4188 102.7 329.9 300.6 888.1 1188.7 4.3390 104.7 331.2 302.1 887.0 1189.1 4.2592 106.7 332.6 303.5 885.8 1189.3 4.1794 108.7 333.9 304.9 884.8 1189.7 4.1096 110.7 335.3 306.3 883.7 1190.0 4.0398 112.7 336.6 307.7 882.6 1190.3 3.96100 114.7 337.9 309.0 881.6 1190.6 3.90102 116.7 339.2 310.3 880.6 1190.9 3.83104 118.7 340.5 311.6 879.6 1191.2 3.77106 120.7 341.7 313.0 878.5 1191.5 3.71108 122.7 343.0 314.3 877.5 1191.8 3.65110 124.7 344.2 315.5 876.5 1192.0 3.60112 126.7 345.4 316.8 875.5 1192.3 3.54114 128.7 346.5 318.0 874.5 1192.5 3.49116 130.7 347.7 319.3 873.5 1192.8 3.44118 132.7 348.9 320.5 872.5 1193.0 3.39120 134.7 350.1 321.8 871.5 1193.3 3.34125 139.7 352.8 324.7 869.3 1194.0 3.23130 144.7 355.6 327.6 866.9 1194.5 3.12135 149.7 358.3 330.6 864.5 1195.1 3.02140 154.7 360.9 333.2 862.5 1195.7 2.93145 159.7 363.5 335.9 860.3 1196.2 2.84150 164.7 365.9 338.6 858.0 1196.6 2.76155 169.7 368.3 341.1 856.0 1197.1 2.68160 174.7 370.7 343.6 853.9 1197.5 2.61165 179.7 372.9 346.1 851.8 1197.9 2.54170 184.7 375.2 348.5 849.8 1198.3 2.48175 189.7 377.5 350.9 847.9 1198.8 2.41180 194.7 379.6 353.2 845.9 1199.1 2.35185 199.7 381.6 355.4 844.1 1195.5 2.30190 204.7 383.7 357.6 842.2 1199.8 2.24195 209.7 385.7 359.9 840.2 1200.1 2.18200 214.7 387.7 362.0 838.4 1200.4 2.14210 224.7 391.7 366.2 834.8 1201.0 2.04220 234.7 395.5 370.3 831.2 1201.5 1.96230 244.7 399.1 374.2 827.8 1202.0 1.88240 254.7 402.7 378.0 824.5 1202.5 1.81250 264.7 406.1 381.7 821.2 1202.9 1.74260 274.7 409.3 385.3 817.9 1203.2 1.68270 284.7 412.5 388.8 814.8 1203.6 1.62280 294.7 415.8 392.3 811.6 1203.9 1.57290 304.7 418.8 395.7 808.5 1204.2 1.52300 314.7 421.7 398.9 805.5 1204.4 1.47310 324.7 424.7 402.1 802.6 1204.7 1.43320 334.7 427.5 405.2 799.7 1204.9 1.39330 344.7 430.3 408.3 796.7 1205.0 1.35340 354.7 433.0 411.3 793.8 1205.1 1.31350 364.7 435.7 414.3 791.0 1205.3 1.27360 374.7 438.3 417.2 788.2 1205.4 1.24370 384.7 440.8 420.0 785.4 1205.4 1.21380 394.7 443.3 422.8 782.7 1205.5 1.18390 404.7 445.7 425.6 779.9 1205.5 1.15400 414.7 448.1 428.2 777.4 1205.6 1.12420 434.7 452.8 433.4 772.2 1205.6 1.07440 454.7 457.3 438.5 767.1 1205.6 1.02

Boilers & Boiler EfficiencyBoilers and the associated fir-

ing equipment should be designedand sized for maximum efficiency.Boiler manufacturers haveimproved their equipment designsto provide this maximum efficien-cy, when the equipment is new,sized correctly for the load condi-tions, and the firing equipment isproperly tuned. There are manydifferent efficiencies that areclaimed when discussing boilersbut the only true measure of aboiler’s efficiency is the Fuel-to-Steam Efficiency. Fuel-To-Steamefficiency is calculated usingeither of two methods, as pre-scribed by the ASME Power TestCode, PTC4.1. The first methodis input-output. This is the ratio ofBTU’s output divided by BTU’sinput, multiplied by 100. The sec-ond method is heat balance. Thismethod considers stack tempera-ture and losses, excess air levels,and radiation and convectionlosses. Therefore, the heat bal-ance calculation for fuel-to-steamefficiency is 100 minus the totalpercent stack loss and minus thepercent radiation and convectionlosses.

The sizing of a boiler for aparticular application is not a sim-ple task. Steam usages varybased upon the percentage ofboiler load that is used for heatingversus process and then combin-ing those loads. Thesepotentially wide load variationsare generally overcome byinstalling not just one large boilerbut possibly two smaller units or alarge and a small boiler to accom-modate the load variations.Boiler manufacturers usually willrecommend that the turndownratio from maximum load to lowload not exceed 4:1. Turndownratios exceeding 4:1 will increasethe firing cycles and decreaseefficiency.

A boiler operating at low loadconditions can cycle as frequent-ly as 12 times per hour, or 288times a day. With each cycle,pre- and post-purge air flowremoves heat from the boiler andsends it out the stack. This ener-gy loss can be eliminated bykeeping the boiler on at low firingrates. Every time the boilercycles off, it must go through aspecific start-up sequence forsafety assurance. It requires

Steam Generation

10

about one to two minutes toplace the boiler back on line.And, if there’s a sudden loaddemand, the start-up sequencecannot be accelerated. Keepingthe boiler on line assures thequickest response to loadchanges. Frequent cycling alsoaccelerates wear of boiler com-ponents. Maintenance increasesand, more importantly, thechance of component failureincreases.

Once the boiler or boilershave been sized for their steamoutput, BTU’s or lb./hr, then theoperating pressures have to bedetermined. Boiler operatingpressures are generally deter-mined by the system needs as toproduct/process temperaturesneeded and/or the pressure loss-es in transmission of the steam indistribution throughout the facili-ty. (Fig. 4)

Figure 3 (Cont.): Steam Saturation Table

Gauge Absolute Temperature Sensible Latent Total (hg) Specific Pressure Pressure Degrees F (hf) (hfg) BTU/lb Volume

psig psia BTU/LB BTU/lb ft3/lb Steam (Vg)

460 474.7 461.7 443.4 762.1 1205.5 .98480 494.7 465.9 448.3 757.1 1205.4 .94500 514.7 470.0 453.0 752.3 1205.3 .902520 534.7 474.0 457.6 747.5 1205.1 .868540 554.7 477.8 462.0 742.8 1204.8 .835560 574.7 481.6 466.4 738.1 1205.5 .805580 594.7 485.2 470.7 733.5 1204.2 .776600 614.7 488.8 474.8 729.1 1203.9 .750620 634.7 492.3 479.0 724.5 1203.5 .726640 654.7 495.7 483.0 720.1 1203.1 .703660 674.7 499.0 486.9 715.8 1202.7 .681680 694.7 502.2 490.7 711.5 1202.2 .660700 714.7 505.4 494.4 707.4 1201.8 .641720 734.7 508.5 498.2 703.1 1201.3 .623740 754.7 51.5 501.9 698.9 1200.8 .605760 774.7 514.5 505.5 694.7 1200.2 .588780 794.7 517.5 509.0 690.7 0099.7 .572800 814.7 520.3 512.5 686.6 1199.1 .557

Steam Generation

11

Selection of Working Pres-sure

The steam distribution sys-tem is an important link betweenthe steam source and the steamuser. It must supply good qualitysteam at the required rate and atthe right pressure. It must do thiswith a minimum of heat loss, andbe economical in capital cost.

The pressure at which thesteam is to be distributed is deter-mined by the point of usage in theplant needing the highest pres-sure. We must rememberhowever that as the steam pass-es through the distributionpipework, it will lose some of itspressure due to resistance toflow, and the fact that some of itwill condense due to loss of heatfrom the piping. Therefore,allowance should be made forthis pressure loss when decidingupon the initial distribution pres-sure.

Summarizing, we need toconsider when selecting ourworking pressure:

• Pressure required at point ofusage

• Pressure drop along pipe dueto resistance of flow (friction)

• Pipe heat losses

It is a recommended practiceto select a boiler operating pres-sure greater than what is actuallyrequired.

This is an acceptable practiceas long as it is understood thatselecting a boiler with a muchgreater operating pressure thanis required, then operating it atthe lower pressure will cause aloss in efficiency of the boiler.This efficiency loss comes fromthe increased radiation and con-vection losses. Another area ofefficiency loss comes from thelower quality (dryness) of thesteam produced due to increased

water level in the boiler and theincreased steam bubble sizebecause of the lower operatingpressures internally. It is alwaysrecommended to operate theboiler at or as close to the maxi-mum operating pressure that thevessel was designed for. Theboilers operating pressure (Fig. 4)has a definite impact on thepotential of priming and carry-over which can cause seriousproblems not only for the systembut for the boiler also.

Many of the boiler manufac-turers today design theirequipment to provide 99.5% drysaturated steam to be generatedand admitted into the distributionsystem. This means that lessthan 1/2 of 1% of the volume exit-ing the boiler will be water, notsteam. In practice, steam oftencarries tiny droplets of water withit and cannot be described as drysaturated steam. Steam qualityis described by its dryness frac-

Boiler Operating at DesignPressure

Boiler Operating at ReducedPressure from Design

• Design Pressure

• Smaller Specific Volume

• Greater Separation Area

• Dry Steam

• Proper Steam Velocities(4 to 6,000 fpm)

• Lower Pressure

• Greater Specific Volume

• Decreased Separation Area

• Lower Quality of Steam

• Increased Steam Velocities

tion, the portion of completely drysteam present in the steam beingconsidered. The steam becomeswet if water droplets in suspen-sion are present in the steamspace, carrying no latent heatcontent.

For example (Fig. 3), thelatent heat energy of 100 PSIGsteam is 881 BTU’s (assuming99.5% dryness) but, if this steamis only 95% dry, then the heatcontent of this steam is only .95 X881 = 834 BTU’s per pound. Thesmall droplets of water in wetsteam have weight but occupynegligible space. The volume ofwet steam is less than that of drysaturated steam. Therefore,steam separators are used atboiler off takes to insure dry qual-ity steam.

Figure 4

can be insulated. A single foot of3" pipe with 100 PSI steam in itexposed to an ambient tempera-ture of 60°F will radiate 778BTU’s per hour of operation. Thelatent heat energy content of 100PSI steam is 880 BTU’s perpound.

Nearly a pound of steam perhour per foot of pipe is con-densed just in distributing thisvaluable energy supply to thepoint of usage. Flanges, valves,strainers and equipment willwaste much more energy than a

Steam Generation

12

Steam VelocityThe velocity of the steam flow

out of the boiler, at designedoperating pressure, is establishedby the outlet nozzle of the boileritself. Target velocities of 6,000fpm or less have become com-monplace as design criteria.These lower velocities provide forreduced pressure losses, moreefficient condensate drainage,reduced waterhammer potentialand piping erosion.

It is important that the steamvelocity, piping and nozzle sizing,be considered when selecting theboiler operating pressurerequired.

Noise is not the only reasonvelocities in a steam systemshould be kept as low as practi-cal. Steam is generated anddistributed throughout the systemand because of temperature dif-ferences in the surroundings andthe insulation losses, the steamgives up its heat and condenses.Although it may not travel as fastas the steam, the condensate(water) is still going to erode thebottom of the pipe. This erosionis accelerated with the velocity ofthe steam, therefore the lower thesteam velocity, the less erosionwill take place.

The chart (Fig. 5) will be veryhelpful in sizing steam carryingpipes for proper velocities.

EXAMPLE:

Steam flow is 1,000 lb/hr.

Find pipe size for 100 psig and 25psig.

The steam system piping andassociated equipment, containingthis high heat energy source(steam), will constantly be asource of radiation losses. A sim-ple but often overlooked energysavings is to insulate all the pip-ing, steam and condensate, andall heat exchange equipment that

Multiply chart velocityby factor below to getvelocity in schedule

80 pipePipe Size Factor

1/2"3/4" & 1"

1-1/4" & 1-1/2"2" to 16"

1.301.231.171.12

20000

12000100008000

600050004000

3000

2000

1000

5000040000

30000

20000

10000

8000

600050004000

3000

2000

1000800

600

100

200

300

400500

Cap

acit

y lb

/h

ReasonableSteam Velocities

in Pipes

Process Steam8000 to 12000 ft/min

Heating Systems4000 to 6000 ft/min

Vel

oci

ty f

t/m

in

Steam Pressure psig(Saturated Steam)

Steam Velocity Chart

Pipe Size(Schedule 40 pipe)

25020015012510075

50

25

1050

25020015012510075

50

25

1050

16"

14"12"

10"

8"

6"

4"

3"

2"

1"1-1/4"

5"

3/4"

1/2"

EA

D

G

C

F

B

2-1/2"

1-1/2"

Figure 5: Steam Velocity Chart

single foot of pipe. The net effectis the consumption of more fuel toproduce this lost energy. (Fig. 6)

Selection of Working Pressures

13

Air and Non-CondensableGases In The Steam System

We know that when steamcomes into contact with a coolersurface, it gives up its latent heatand condenses. As condensationtakes place, the condensatebegins to form a film of water(Fig. 7). It is a fact that water hasa surprisingly high resistance toheat transfer. A film of water only1/100 inch thick offers the sameresistance to heat transfer as a1/2 inch thick layer of iron or a 5inch thick layer of copper. The airand other non-condensablegases in the steam cause a vari-ety of problems to steamsystems. Foremost is the reduc-tion of area to deliver the steam.Air is a simple bi-product ofsteam generation. It is in allsteam systems and should bedealt with accordingly. Where theair will collect in the system is theproblem.

Air and other non-condens-able gases are released whensteam is generated and passesdown the distribution with thesteam. It will collect in areas ofhigh steam consumption such asheat exchangers, but will also col-lect at high points and at the endof the steam piping. If a steamline feeds a series of heatexchangers, such as cooking ket-tles, the air collects at the end of

the main line. The last kettle,therefore, would be fed with amixture of steam and non-con-densable gases.

Air cannot hold the tempera-ture or latent heat of steam. Itwill, therefore, cause a reductionin temperature first of all. Air, itshould be remembered, is aninsulator. (Fig. 7) It is generallyaccepted that a thin layer of aironly 0.04 inches thick can offerthe same resistance to the flow ofheat as a layer of water 1 inchthick, a layer of iron 4.3 feet thickor a layer of copper 43 feet thick.Even a small amount of air in asteam system will cause fairlydrastic temperature losses, an

example would be 100 PSIG sat-urated steam has a temperatureof 338°F, if in this steam thereexisted a 10% by volume mixtureof air the equivalent temperatureof this mixture would be 331°F, orthe steam temperature of 90PSIG not 100 PSIG.

Another major problem withair in the steam system is that itwill be absorbed into the conden-sate. This reduces the pH of thecondensate and creates a sub-stance known as carbonic acid.The acidity of the condensate willthen attack the piping, heatexchange equipment or any otherpart of the steam system that itcomes into contact with.

Figure 6: Pipeline Heat Loss Table - BTU’s/Hr/Ft

2" 4" 2" 4" 2" 4" 2" 4" 2" 4" 2" 4" 2" 4"

80 66 41 77 47 89 53 109 63 132 75 153 8 166 92

150 123 77 14 87 166 99 205 120 247 140 286 161 311 173

200 164 10 19 117 221 131 274 159 329 187 382 214 415 231

250 205 12 240 146 276 164 342 199 412 235 477 268 519 288

300 246 153 288 175 331 198 411 238 495 281 573 321 622 346

350 288 178 336 205 386 230 478 278 576 328 668 375 726 404

Process Pipeline Diameter and Insulation Thickness

4 5" 6" 8" 10" 12" 14"Insulation Thickness

Pro

duct

/Am

bien

t

Tem

pera

ture

Diff

eren

ce D

eg F

˚

Figure 7The Practical Effect of Air & Water Films

250°F

210°F

Steamat 15psi

AirFilm

CondensateFilm

WaterBeing

Heated

WaterFilm

MetalHeatingSurface

Steam System Basics

14

Steam System BasicsFrom the outset, an under-

standing of the basic steamcircuit, ‘steam and condensateloop’ (Fig. 9) is required. Thesteam flow in a circuit is due tocondensation of steam whichcauses a pressure drop. Thisinduces the flow of steam throughthe piping.

The steam generated in theboiler must be conveyed throughpipework to the point where it’sheat energy is required. Initiallythere will be one or more mainpipes or “steam mains” whichcarry the steam from the boiler inthe direction of the steam usingequipment. Smaller branch pipescan then carry the steam to theindividual pieces of equipment.

When the boiler crown valveis opened admitting the steaminto the distribution piping net-work, there immediately begins aprocess of heat loss. These loss-es of energy are in the heating upof the piping network to the steamtemperature and natural losses tothe ambient air conditions. Theresulting condensate falls to thebottom of the piping and is car-

ried along with the steam flowalong the steam main. This con-densate must be drained fromthis piping or severe damage willresult.

When the valves serving theindividual pieces of equipmentcall for steam, the flow into theheat exchange equipment beginsagain causing condensation andthe resultant pressure drop whichinduces even more flow.

Figure 9A Typical Steam Circuit

Steam

Steam

Boiler Feed Pump

Feed Tank

Condensate

CondensateMake-up Water

ProcessVessels

Space Heating System

Pans

Vats

The use of Thermostatic AirVents will help remove the accu-mulating air and rid the system ofthe adverse effects. Air Vents arenothing more than thermostatical-ly-actuated steam trapspositioned in the system wherethe air will collect. Proper designprocedures require air vents to belocated at high points, at the endof the steam main piping, (Fig. 8)and on all heat exchange equip-ment.

Figure 8Air Venting and Steam Trapat End of Main

Steam MainBalancedPressure

ThermostaticAir Vent

Thermo-dynamicSteam Trap Setwith Trap Tester

Drip Leg

Steam System Basics

15

Steam Piping Design Consid-erations

Since we have already estab-lished that steams principle job isto give up its latent heat energyand re-condense to water, bydoing so, we can assume that itwill do so anywhere and every-where (Fig. 10) because all heatflow is from hot to cold. When thesteam is admitted into the distrib-ution piping network, the steamimmediately begins to heat the

piping. This transfer of heat ener-gy creates condensate, (Fig. 11and 12) or if the piping is alreadyat the same temperature as thesteam, there are still loses to theambient air conditions, evenwhen insulated. This liquid con-densate would continue to buildup to the point of blocking all ofthe steam piping if it is not prop-erly removed, and createwaterhammer in the steam sys-tem. Periodically in a steam

distribution main piping network,condensate “drip stations” needto be installed to remove this con-densate from the system. Thesepockets should be designed withas much care as possible. Thisallows the condensate a low pointin which to drop out of the steamflow and be removed by steamtraps.

Figure 10Terms

Steam Header

Steam Line Reducer

Steam Branch Line

Steam Separator

Steam Drip Stations (Pockets)

Steam Strainer

Steam Distribution (to Higher Levels)

Steam System Basics

16

Ambient Temperature 70°F. Insulation 80% efficient.Load due to radiation and convection for saturated steam.

Ambient Temperature 70°F. Based on Sch. 40 pipe to 250 psi

Sch. 80 above 250 except Sch. 120 5" and larger above 800 psi

Figure 11: Warm-Up Load in Pounds of Steam per 100 Ft. of Steam Main

Figure 12: Running Load in Pounds per Hour per 100 Ft. of Insulated Steam Main

Steam Main Size 0˚FPressure Correction

psi 2" 2-1/2" 3" 4" 5" 6" 8" 10" 12" 14" 16" 18" 20" 24" Factor *0 6.2 9.7 12.8 18.2 24.6 31.9 48 68 90 107 140 176 207 308 1.505 6.9 11.0 14.4 20.4 27.7 35.9 48 77 101 120 157 198 233 324 1.44

10 7.5 11.8 15.5 22.0 29.9 38.8 58 83 109 130 169 213 251 350 1.4120 8.4 13.4 17.5 24.9 33.8 44 66 93 124 146 191 241 284 396 1.3740 9.9 15.8 20.6 90.3 39.7 52 78 110 145 172 225 284 334 465 1.3260 11.0 17.5 22.9 32.6 44 57 86 122 162 192 250 316 372 518 1.2980 12.0 19.0 24.9 35.3 48 62 93 132 175 208 271 342 403 561 1.27

100 12.8 20.3 26.6 37.8 51 67 100 142 188 222 290 366 431 600 1.26125 13.7 21.7 28.4 40 55 71 107 152 200 238 310 391 461 642 1.25150 14.5 23.0 30 43 58 75 113 160 212 251 328 414 487 679 1.24175 15.3 24.2 31.7 45 61 79 119 169 224 265 347 437 514 716 1.23200 16.0 25.3 33.1 47 64 83 125 177 234 277 362 456 537 748 1.22250 17.2 27.3 35.8 51 69 89 134 191 252 299 390 492 579 807 1.21300 25.0 38.3 51 75 104 143 217 322 443 531 682 854 1045 1182 1.20400 27.8 43 57 83 116 159 241 358 493 590 759 971 1163 1650 1.18500 30.2 46 62 91 126 173 262 389 535 642 825 1033 1263 1793 1.17600 32.7 50 67 98 136 187 284 421 579 694 893 1118 1367 1939 1.16800 38.0 58 77 113 203 274 455 670 943 1132 1445 1835 2227 3227 1.156

1000 45 64 86 126 227 305 508 748 1052 1263 1612 2047 2485 3601 1.1471200 52 72 96 140 253 340 566 833 1172 1407 1796 2280 2767 4010 1.1401400 62 79 106 155 280 376 626 922 1297 1558 1988 2524 3064 4440 1.1351600 71 87 117 171 309 415 692 1018 1432 1720 2194 2786 3382 4901 1.1301750 78 94 126 184 333 448 746 1098 1544 1855 2367 3006 3648 5285 1.1281800 80 97 129 189 341 459 764 1125 1584 1902 2427 3082 3741 5420 1.127

* For outdoor temperature of 0°F, multiply load value in table for each main size by correction factor shown

Steam Main Size 0°FPressure Correction

psi 2" 2-1/2" 3" 4" 5" 6" 8" 10" 12" 14" 16" 18" 20" 24" Factor *10 6 7 9 11 13 16 20 24 29 32 36 39 44 53 1.5830 8 9 11 14 17 20 26 32 38 42 48 51 57 68 1.5060 10 12 14 18 24 27 33 41 49 54 62 67 74 89 1.45

100 12 15 18 22 28 33 41 51 61 67 77 83 93 111 1.41125 13 16 20 24 30 36 45 56 66 73 84 90 101 121 1.39175 16 19 23 26 33 38 53 66 78 86 98 107 119 142 1.38250 18 22 27 34 42 50 62 77 92 101 116 126 140 168 1.36300 20 25 30 37 46 54 68 85 101 111 126 138 154 184 1.35400 23 28 34 43 53 63 80 99 118 130 148 162 180 216 1.33500 27 33 39 49 61 73 91 114 135 148 170 185 206 246 1.32600 30 37 44 55 68 82 103 128 152 167 191 208 232 277 1.31800 36 44 53 69 85 101 131 164 194 214 244 274 305 365 1.30

1000 43 52 63 82 101 120 156 195 231 254 290 326 363 435 1.271200 51 62 75 97 119 142 185 230 274 301 343 386 430 515 1.261400 60 73 89 114 141 168 219 273 324 356 407 457 509 610 1.251600 69 85 103 132 163 195 253 315 375 412 470 528 588 704 1.221750 76 93 113 145 179 213 278 346 411 452 516 580 645 773 1.221800 79 96 117 150 185 221 288 358 425 467 534 600 667 800 1.21

* For outdoor temperature of 0°F, multiply load value in table for each main size by correction factor shown.

Steam and Condensate Metering

17

The proper design of thesedrip stations is fairly simple. Themost common rules to follow are:

1. Drip Stations on steammains must be located at alllow points in the system, ele-vation changes, directionalchanges, expansion loopsand at all dead ends.

2. In the horizontal run of thesteam main piping drip sta-tions must be located atregular intervals of 100 to200 feet.

3. The drip station itself is asection of piping connectedto the bottom of the mainpiping. The diameter of thedrip station pipe should bethe same size as the steammain piping up to 6" piping.For steam main piping largerthan 6" the drip station pip-ing shall be 1/2 the nominalpipe size but no less than 6".

4. The vertical drop of the dripstation shall be 1-1/2 timesthe diameter of the steammain but not less than 18inches.

5. Horizontal run of the steampiping must fall 1/2" in 10feet towards drip stations.

The reasoning behind theserules is simple. First, the diame-ter of the hole in the bottom of thesteam main should be such that itcan allow the water ample area tofall into. Gravity is our only forceto allow this to happen. If thediameter of the drip station wastoo small, the velocity of thewater would simply allow it topass either on the side or overthe top of the hole. The length ofthe drip station allows the waterto fall far enough out of the steamflow as to not be pulled back outand forced on down the piping,and to provide the steam trapwith some hydraulic head pres-sure for drainage of condensateduring the low pressure times of

Although steam metering is most often carried out in the boilerhouse, it is also important in order to determine:

1. Custody transfer. To measure steam usage and thus determinesteam cost:

a) Centrally at the boiler house

b) At all major steam using areas

2. Equipment efficiency. Identifying major steam users, when loadedto capacity or idle; also peak load times, plant deterioration andcleaning requirements.

3. Process control. Meters indicate that the correct steam requirementand quantity is supplied to a process, when bypass lines areopened; and when valves and steam traps need attention.

4. Energy efficiency. Compare the efficiency of one process area withanother; monitor the results of plant improvements and steam sav-ing programs.

Figure 13A Typical Steam Metering Station

shut down and start-up of thesteam main. Remember, theintent of the distribution line is todeliver steam at as high a qualityas possible to the heat processequipment. The equipmentdownstream will suffer severedamage if we don’t do this stepcorrectly.

Steam and CondensateMetering

Difficulties in energy manage-ment of steam arise from the factthat it is often a totally unmeasuredservice. Metering (Fig. 13) startingin the boiler house, is essential ifsavings are to be validated.Although fuel consumption is fairlyeasy to monitor, measurement ofsteam is a bit more difficult. Asteam meter must compensate forquality as well as pressure, specif-ic volume and temperature.

Performance of different types ofmeters when used on steam willvary and the measurement maynot always be accurate. Mostmeters depend on a measurementof volume. Since volume dependson pressure, measurements needto be taken at a constant pressureto the meter or else specific cor-rections have to be applied.Readings taken under fluctuatingpressure conditions are inaccurateunless the meter can automaticallycompensate.

Steam metering should bedone downstream of a good quali-ty reducing valve which maintainsa constant pressure. Readingsshould be interpreted using themeter factor and the meter calibra-tion should be checked from timeto time.

PipelineStrainer

SteamSeparator

SteamMeter

Separator&Trap Set

EccentricReducers

6 PipeDiameters

3 PipeDiameters

Steam and Condensate Metering

18

Why Measure Steam?Steam is still the most widely

used heat carrying medium in theworld. It is used in the processesthat make many of the foodstuffswe eat, the clothes we wear, com-ponents of the cars we ride in andthe furniture we use. It is used inhospitals for sterilization of instru-ments and surgical packs, in therefining process for crude oilbased products, in chemical pro-duction, and in the laundry thatcleans our clothes.

Despite this, it is commonlyregarded as an almost free ser-vice - easily available. Very fewattempt to monitor its usage andcosts, as they would for other rawmaterials in the process.

"But a steam meter won'tsave energy''. This statement issometimes used as a reason fornot installing steam meters. Itcannot be argued against ifsteam meters are evaluated inthe same way as other pieces ofenergy saving equipment orschemes.

A statement such as the onequoted earlier does little to easethe frustration of the EnergyManager or Factory Manager try-ing to establish where steam isbeing used, how much is beingused and whether it is being usedwisely and effectively.

All too often, when the needfor a steam meter is accepted,only central monitoring i.e. in theBoiler House or a major PlantRoom is carried out. Monitoring atbranch mains or at each plantroom, a section of the process ormajor pieces of steam usingequipment, are not considered.

While central monitoring willestablish overall steam flow fig-ures (and thus, costs),’departmental' monitoring willgive data which is much moreuseful. Such steam meters will

enable checks to be kept on indi-vidual plant performance. Costscan be analyzed for each part ofthe process and ‘pay-back'records can be established fol-lowing the implementation ofenergy saving measures.

The steam meter is the firstbasic tool in good steam house-keeping - it provides theknowledge of steam usage andcost which is vital to an efficientlyoperated plant or building. Themain reasons for using a steammeter are, therefore:-

Plant EfficiencyA steam meter will indicate

process efficiency. For example,whether idle machinery isswitched off; whether plant isloaded to capacity and whetherworking practices are satisfacto-ry. It will also show thedeterioration of plant overtime,allowing optimal plant cleaning oreven replacement, to be calculat-ed. Further, it can establish peaksteam usage times or identifysections or items of plant whichare major steam users. This maylead to a change in productionmethods to even out steam usageand ease the peak load problemson boiler plant.

Energy EfficiencySteam meters can be used to

monitor the results of energy sav-ing schemes and to compare theefficiency of one piece of plantwith another.

Process ControlSteam meters can indicate

that the correct quantity of steamis being supplied to a processand that it is at the correct tem-perature and pressure.

Costing and Custody TransferSteam meters can measure

steam usage and thus steamcost.

(a) Centrally

(b) At major steam usingcenters.

Steam can be costed as a'raw material' at various stages ofthe production process thusallowing the true cost of individualproduct lines to be calculated.

The Control and Regulation ofSteam

The proper control and regu-lation of steam either in regardsto steam pressure for equipmentor for the flow of this valuableheat energy source to heat trans-fer equipment is mandatory fortoday’s industrial and HVACsteam users for efficient usage ofthis energy source. The control ofheat flow to product temperaturesin process equipment is manda-tory, otherwise productionwastage becomes intolerable,which means lost profits.

The control of steam pres-sures and the regulation of steamflow to heat exchangers isaccomplished by several differenttypes of valves. This section isintended to describe the differenttypes of valves used for theseoperations and the differencesthat will help the user in decidingwhich type of valve is necessaryfor his specific application. Thissection will not go into completedescriptions of these valves butjust an overview of their opera-tional characteristics and thebenefits of that operation.

Pressure Reducing ValvesMost steam boilers are

designed to work at relativelyhigh pressures, generally abovethe steam pressure required inequipment, and should not beoperated at lower pressures.Operation at lowered pressurescauses reduced efficiencies andincreased potential for boiler car-ryover. For this reason, thehighest efficiency is maintainedby generating and distributing thehighest steam pressures that theboiler is capable of producing. Toproduce lower pressure steam atthe point of use, a building pres-sure reducing valve should beused. This system design allowsfor much smaller distribution pip-ing, reducing costs and reducingheat losses from these pipes.Also every piece of steam usingequipment has a maximum safeworking pressure which cannotbe exceeded in operation.Another energy efficiency reasonfor reducing steam pressures isthe “latent” heat content is greaterin lower pressure steam. Moreheat content per pound meansless pounds of steam to do thework. These are not the only rea-sons for reducing steampressure. Since the temperatureof saturated steam is determinedby its pressure, control of pres-sure is a simple but effectivemethod of accurate temperaturecontrol. This fact is used in appli-cations such as sterilizers andcontrol of surface temperatureson contact dryers. Reducingsteam pressure will also cut downon the losses of flash steam fromvented condensate returnreceivers.

Most pressure reducingvalves currently available can bedivided into three groups andtheir operation is as follows:

Direct Acting Control ValvesThe direct acting valve is the

simplest design of reducing valve(Fig. 14a). Reduced pressurefrom downstream of the valveacts on the underside of thediaphragm “A”, opposing thepressure applied by the controlspring “B”. This determines theopening of the main valve “C” andthe flow through the reducingvalve.

In order for the valve to movefrom open to the closed position,there must be a build up of pres-sure under the diaphragm “A”.This overcomes the pressureexerted by the control spring “B”.This action results in an inevitablevariation of the downstream pres-sure. It will be the highest whenthe valve is closed, or nearlyclosed, and will “droop” as theload demand increases. The out-let pressure acting on the

underside of the diaphragm tendsto close the valve as does theinlet pressure acting on theunderside of the main valve itself.The control spring must be capa-ble of overcoming the effects ofboth the reduced and inlet pres-sures when the downstreampressure is set. Any variation inthe inlet pressure will alter theforce it produces on the mainvalve and so affect the down-stream pressure. This type ofvalve has two main drawbacks inthat it allows greater fluctuation ofthe downstream pressure, underunstable load demands, andthese valves have relatively lowcapacity for their size. It is never-theless perfectly adequate for awhole range of simple applica-tions where accurate control isnot essential and where thesteam flow is fairly small andreasonably constant.

Control and Regulation of Steam

19

Figure 14aDirect Acting Pressure Reducing Valve

A

Inlet Outlet

B

C

small. Although any rise inupstream pressure will apply anincreased closing force on themain valve, this is offset by theforce of the upstream pressureacting on the main diaphragm.The result is a valve which givesclose control of downstreampressure regardless of variationson the upstream sides (Fig. 16).

Pneumatically OperatedValves

Pneumatically operated con-trol valves with actuators andpositioners (Fig. 15) being piloted

Control and Regulation of Steam

20

Pilot Operated ValvesWhere accurate control of

pressure or large capacity isrequired, a pilot operated reduc-ing valve (Fig. 14b) should beused.

Reduced pressure acts onthe underside of the pilotdiaphragm “C”, either through thepressure control pipe “F”, so bal-ancing the load produced on thetop of the pilot diaphragm by thepressure of the adjustment spring“B”.

When the downstreamreduced pressure falls, “F” thespring force overcomes the pres-sure acting below the pilotdiaphragm and opens the pilotvalve “E”, admitting steam throughthe pressure control piping “D” tothe underside of the maindiaphragm “K”. In turn, this opensthe main valve “H” against itsreturn spring “G” and allows moresteam to pass until the down-stream pressure returns to thepreset value.

Any further rise in reducedpressure will act on the pilotdiaphragm to close the pilot valve.Pressure from below the maindiaphragm will then be relievedinto the valve outlet back throughthe control pressure piping “D”and the orifice “J” as the returnspring moves the main valvetowards its seat, throttling theflow.

The pilot valve will settledown to an opening which is justsufficient to balance the flowthrough the orifice “J” and main-tain the necessary pressure underthe diaphragm to keep the mainvalve in the required position forthe prevailing upstream anddownstream pressure and loadconditions. Any variation in pres-sure or load will be sensedimmediately by the pilotdiaphragm, which will act to adjustthe position of the main valve.

The reduced pressure is setby the screw “A” which alters thecompression of the adjustmentspring “B”.

The pilot operated designoffers a number of advantagesover the direct acting valve. Onlya very small amount of steam hasto flow through the pilot valve topressurize the main diaphragmchamber and fully open the mainvalve. Thus, only very smallchanges in downstream pressureare necessary to produce largechanges in flow. The “droop” ofpilot operated valves is, therefore,

Figure 14bPilot Operated Reducing Valve

A

B

C

D

E

G

A F

H

J

K

Inlet

L

Selection & ApplicationThe first essential is to select

the best type of valve for a givenapplication and this follows logically from the descriptionsalready given. Small loads whereaccurate control is not vitalshould be met by using the sim-ple direct acting valves. In allother cases, the pilot operatedvalves will be the best choice,particularly if there are periods ofno demand when the downstream pressure must notbe allowed to rise.

Oversizing, a common industry practice, should beavoided at all costs regardless of

Control and Regulation of Steam

21

Figure 15Pneumatic Pressure Reducing Valve

Figure 16Pressure Reducing Station Installation

the type of control valve selected.A valve that is too large in capacity capabilities will have towork with minimum openingbetween the valve head and seaton less than maximum loadswhich can and does cause wire-drawing, valve cutting, anderosion. In addition, any smallmovement of the oversized headwill produce a relatively largechange in the flow through thevalve orifice in an effort to accommodate load changes,almost always allowing more orless flow through the valve thanwas actually needed causinglarger pressure fluctuationsdownstream.

by controllers will provide pres-sure reduction with even moreaccurate control. Controllerssense downstream pressure fluc-tuations interpolate the signalsand regulate an air supply signalto a pneumatic positioner whichin turn supplies air to adiaphragm opening a valve.Springs are utilized as an oppos-ing force causing the valves toclose upon loss of or a reductionof air pressure applied on thediaphragm. Industry sophistica-tion and control needs aredemanding closer and moreaccurate control of steam pres-sures, making Pneumatic controlvalves much more popular today.

High PressureDecrease Piping Size

SteamSeparator

SteamSeparator

Strainer(On Side)

Air Supply

Safety Relief Valve

Safety Relief Valve

Low PressureIncrease Piping Size

IN

IN

OUT

OUT

Control and Regulation of Steam

22

A smaller, correctly sizedreducing valve will be less proneto wear and will give more accu-rate control. Where it isnecessary to make bigger reduc-tions in pressure or to cope withwide fluctuations in loads, it isrecommended to use two or morevalves in series or parallel toimprove controllability and lifeexpectancy of the valves.

Although reliability and accu-racy depend on correct selectionand sizing, they also depend oncorrect installation.

Since the majority of reduc-ing valve problems are caused bythe presence of wet steam and/ordirt, a steam separator andstrainer with a fine mesh screen(100 mesh) are fitted before thevalve. The strainer is installedwith the “Y” portion of its body justbelow horizontal in a horizontalsteam line to prevent the bodyfrom filling up with condensateduring periods of shut down andto ensure that the full area of thescreen is effective in preventingdirt from passing through. As apart of a PreventativeMaintenance Program all strain-ers should be installed withblowdown valves for regular dirtremoval. All upstream and down-stream piping and fittings shouldbe sized to handle the maximumsteam flows at a reasonablevelocity of not more than 6,000feet per minute. Eccentric pipereducers, with the flat side on thebottom, should be used to pre-vent any build up of condensatein the piping during shutdown.

If the downstream equipmentis not capable of withstanding thefull upstream steam pressure,then a safety relief valve must befitted either on the downstreampiping or the specific piece ofequipment to be protected fromover pressurization in case of a

valve failure. This safety reliefvalve must be sized to handle themaximum steam flow of thereducing valve at the desired setrelief pressure. ASME standardsstate that those set relief pres-sures are to be 5 PSI above theequipment maximum operatingpressure for equipment operatingup to 70 PSI, and not to exceed10% greater than maximum oper-ating pressures for equipmentoperating above 70 PSI but below1000 PSI.

Temperature Control ValvesMost types of steam equip-

ment need to utilize some form oftemperature control system. Inprocess equipment, product qual-ity is often dependent uponaccurate temperature control,while heating systems need to bethermostatically controlled inorder to maintain optimum com-fort conditions. From an energysaving point of view, controllingthe steam energy supply to aprocess piece of equipment tomaintain the desired product tem-perature, whether air or anyproduct, is mandatory. If processsystems are not controlled to thedesired temperatures then thesystem will run “wild” either notproviding the required heat ener-gy or over heating the product tounacceptable levels. A veryimportant item to remember in theuse of temperature control valveson systems is that in order to reg-ulate the heat energy transferredto the process the control valveeffectively regulates not only theflow rate of energy in pounds perhour, but, also accomplishes tem-perature control by regulating thesaturated steam pressure/tem-perature levels admitted to theprocess heat exchange equip-ment. Temperature control can beaccomplished by several meth-ods and valves:

Manual Control ValvesManual valves can be applied

to a piece of equipment to controlthe energy supplied to theprocess as simply as they areused to regulate the flow of otherfluids. The major drawback ofmanual valves to control temper-atures is that these valves willundoubtedly need frequentadjustments and monitoring tomaintain just the correct tempera-tures under constantly changingload conditions, which is the caseof most pieces of process equip-ment.

Self Acting Control Valves Self-Acting Control Valves

(Fig. 17) are operated by a sen-sor system that senses theproduct temperatures, causing aheat sensitive fluid to expand orcontract based on the producttemperature transferring heatenergy to the sensors fluid. Thisexpansion and contraction of theheat sensitive fluid is transmittedup through a capillary tubingarrangement and the respectiveexpansion and contraction of thefluid applies or relieves pressureto a valve head, causing thevalve head to move. This move-ment allows the control valve tothrottle the steam flow to theequipment. These control sys-tems are calibrated by theamount of heat sensitive fluid tocontrol within a given tempera-ture range and can be set to anytemperature between the upperand lower limits by means of anadjustment knob.

Control and Regulation of Steam

23

Figure 17Self Acting Temperature Control

Figure 18Pilot Operated Temperature Control Valve

Pilot Operated Control ValvesPilot Operated Temperature

Control Valves (Fig. 18) operateon a similar design exceptinstead of operating the controlvalve head movement directly,these units only control a smallpilot device which in turn oper-ates the main valve for throttlingof the steam flow. Since on thisdevice the heat sensitive fluidonly operates a very small valvemechanism, which in turn oper-

ates the main throttling device,the sensing system is muchsmaller in physical size. Thesesystems tend to control therequired temperatures muchcloser to the desired levels and ifand when a load change require-ment occurs, the pilot operatedvalves are able to respond tothese changes much morerapidly.

The normal position beforestarting up the system is with the

main throttling valve closed andthe pilot valve held open byspring force. Entering steampasses through the pilot valveinto the diaphragm chamber andout through the control orifice.Control pressure increases in thediaphragm chamber, whichopens the main valve. As theproduct being heated approachesthe pre-selected desired temper-ature, the heat sensitive fluid inthe sensor bulb expands throughthe capillary tubing into the bel-lows and throttles the pilot valve.The control pressure maintainedin the diaphragm chamber posi-tions the main valve to deliver therequired steam flow. When heatis not required, the main valvecloses tight to provide dead endshut off. The temperature settingcan be changed by turning thecalibrated adjustment dial on thepilot. This type of temperaturecontrol is known as “modulatingcontrol”, since the steam supplyis gradually increased ordecreased in response to anyvariation in the temperature of themedium being heated.Remember that this means thatthe steam pressure in the heatingequipment can and will vary fromrelatively high pressure/tempera-ture when the valve is wide opento practically nothing, or evenpotentially in vacuum conditions.NOTE: A vacuum can form as theresidual steam in the coil or heatexchanger equipment condensesbecause the closed valve pre-vents any further steam fromentering. The most commonoccurrence is coils and/or heatexchanger equipment running invacuum, doing more work thanwhat they were designed for,greater product flows through theequipment causing the steam tobe condensed faster than it canbe admitted.

Adjustment Knob

Sensor

Add 1°C toSensor

Overload Bellows

Valve Housing

Thrust Pin

Capillary

Actuator to ValveConnection

Valve PlugMovement

Movementcaused byAdding Tempto Sensor

TemperatureAdjustment

Control Pressure

TemperaturePilot

Inlet

Orifice

Bulb

Main Valve

Main Diaphragm

Control and Regulation of Steam

24

Pneumatic Control ValvePneumatic Control Valves

(Fig. 19) are also pilot operatedvalves in that they receive theircontrol signals from an externalsensing system, converting thistemperature signal into either acompressed air signal to actuate(throttle) the valve or from a tem-perature signal to an electricalsignal (4-20 MA) which then reg-ulates a compressed air signal tothe valve actuator. Sensitivityand response time to changes ofload condition are enhanced withthis type of valve system.Another benefit of using thisarrangement of control system isthe ability to observe the valvesopening position externally byeither an indicator on the valvestem or by the compressed airsignal applied to the actuator.

The deciding factors for theselection of the proper controlvalve system for a specific appli-cation is certainly the degree ofaccuracy required on the prod-uct’s temperature and theresponse time to load changes ifthere are any.

Figure 19Pneumatic Pilot Operated Temperature Control

Proportional Control BandsSince self-acting controls

require a change in sensor tem-perature to effect a response inthe amount of valve opening, theyprovide a set temperature valuethat is offset in proportion to theload change. The charts on thefollowing page (Figs. 20a and20b) show that the proportionalband of the control describes theamount that the temperature set-ting “droops” at full load. Both setpoint accuracy and system stabil-ity result when the regulator valveis sized for the range of offset rec-ommended. Main valves andpilots are matched so that typical-ly on a 6°F sensor bulb changeresults in full opening of the highcapacity main valve. Pneumaticcontrol valve system’s proportion-al bands are affected by thesensitivity of the sensor and thecontrol signals received from thecompressed air supply or electri-cal signal. Calibration of thesevalves also will dictate their sensi-tivity and certainly the use of acontroller unit will enhance theproportional band characteristics.

On certain applications suchas hot water storage systems,periods of heavy steam demandalternate with periods of nodemand. In such cases, it is pos-sible to use the “on/off” type oftemperature regulator. Here thecontrol thermostat closes off thesteam valve completely when thecontrol temperature is reachedand consequently the steampressure in the primary siderapidly drops to zero. As soon ashot water is drawn off, cold make-up water enters and is sensed bythe control system thermostatwhich opens the steam valvefully, giving a rapid build up ofsteam pressure in the primaryside. This type of control systemwould only be recommended forapplications when the hot water isbeing drawn off at intervals forcleaning usage then there wouldbe a recovery time allowed beforethe next draw off of the system.

This section is essentially abrief introduction to the subject oftemperature control, rather than acomprehensive coverage of themany types of control currently

SteamSeparator Positioner

Actuator

Air Regulator

Temperature

Controller

IN

Control and Regulation of Steam

25

Figure 20aSelected Proportional Band

available for use on steam heatexchange equipment.

When a modulating control isused, the steam trap should becapable of giving continuous con-densate discharge over the fullrange of pressures. If maximumoutput is required from the unit,the trap used must be able to dis-charge condensate and air freelyand must not be of a type which isprone to steam locking. A ther-mostatic trap is not suitablebecause it has a fixed dischargetemperature that may cause con-densate to be held back justwhen the control valve is wideopen and the equipment is callingfor maximum heat transfer.

Traps which give a heavyblast discharge, such as a large

inverted bucket trap, may upsetthe accurate temperature controlof certain units because of thesudden change in pressure in thesteam space which occurs whenthey open. This effect is mostlikely to be noticeable in equip-ment where the steam space hasa high output in relation to itsvolume.

The most suitable type of trapfor temperature controlled appli-cations is the continuousdischarge float and thermostatictrap. This trap will discharge con-densate immediately as it isformed without upsetting pres-sure conditions in the steamspace. It will not steam lock, withproper installation, and will not airlock or attempt to control the dis-

Figure 20bAcceptable P-bands

charge temperature of the con-densate.

If waterhammer is likely tooccur, the float and thermostatictrap is liable to become damaged,for this reason and for thelongevity of the heat exchangeequipment waterhammer situa-tions should be corrected at allcosts. In most cases waterham-mer in heat exchange equipmentis caused by water logging of theequipment. Note: Condensatemust be allowed to drain freely bygravity at all times. If condensatehas to be lifted up into a returnsystem, then this lifting has to bedone by a pumping device.

Control SetValue

Temperature

0% Load Proportional Band(offset = 0°)

SelectedProportional Bandor Offset at FullLoad

100% Loadfor SpecificApplication

0% Load

Application °F P-Band

Hot Water Service Storage Calorifier 7° - 14°F

Central Heating Non Storage Calorifiers 4° - 7°F

Space Heating (Coils, Convectors, Radiators, etc.) 2° - 5°F

Bulk Storage 4° - 18°F

Plating Tanks 4° - 11°F

Load

Steam Traps and the Removal of Condensate

26

Condensate RemovalCondensate should be prop-

erly disposed of from each of thethree possible types of plant loca-tions which are Drip, Tracer andProcess. Condensate has beenneglected in the past, but has adistinct monetary value whichmust be recaptured. It is becom-ing far too valuable to merelydiscard to the ground or a drain.Let us look at some of the impor-tant and valuable aspects ofcondensate.

First of all, condensate ispurified water. It is distilled water.It may have some chemical treat-ment left in it which in itself isvaluable. Most of all though, it ishot water. It is fairly obvious thatit is less expensive to regeneratehot condensate back into steamthan it would be to heat coldmake up water into steam. EveryBTU is valuable and that whichremains in the condensate is noexception.

In the past, the focus of con-densate removal was generally inmain steam process areas only.Condensate from light load loca-tions, such as Drip and Tracer,have not been widely returned.The loads at a drip station are lowfor each location, but when thenumber of locations are counted,it is shown the amount of return-able condensate is very high. Forexample, if we review the expect-ed condensate load from theSteam Distribution CondensateTables (Fig. 12), a six inch steammain at 100 psig will generateabout 33 lbs. per hour per 100 ft.of insulated pipe. This initiallydoes not seem like much, but ifthere are 100 drip locations, itcalculates to approx. 3300 lbs.per hour of condensate. Multiplythis number by 8760 hours in ayear and you will see a substantialamount of usage.

CALCULATION:3300 lbs./hour

x 8760 hrs/ year28,908,000 lbs/year

or 3,412,897 gal./year

Another factor to calculate isthe monetary value of the con-densate. Condensate containsheat, chemicals and water. It isusually as much as one third ofthe cost of generating steam. Ifour example were to assume asteam generation cost of $3.00for each 1,000 lbs., our exampleof lost condensate and energycalculates as follows:

CALCULATION:28,908,000 lbs/year

= 28,9801,000

28,980 x $1.00 = $ 28,980/year

Another small user in asteam system, where condensateis being created and discharged,is that of the tracer lines. Tracersare those lines that follow the flowof process liquids to prevent themfrom freezing or solidifying.Tracer lines, however, are notusually meant to be a type of heatexchanger. They merely followthe path of the process fluids tokeep them hot and less viscous.One of the extreme costs whichare hidden in everyday plant pro-duction is the cost of pumpingliquids from one point to another.Heavy, viscous liquids are obvi-ously more difficult to pump soamperage at the electrical pumpsrises. As amperage rises, electri-cal use rises and so does theamount of money spent on pump-ing liquids.

If the tracer lines do their job,they allow heat to transfer into theproduct liquids as heat is lostthrough the insulation. If the effi-ciency of insulation is relativelygood, the steam usage would bereasonably low. It would not beunusual for this type of tracing togenerate only about 25 lbs/hour.

Again, at first glance this seemsto be only a small user of steamand not worth collecting andreturning. It has much of thesame characteristics as the dripstation condensate in that it ishot, has been chemically treatedand is good quality water. Again,if a plant had 100 tracer lines ofthis type, the usage would calcu-late as follows:

CALCULATION:25 lbs./hour X 100 lines

= 2500 lbs/hour2500 lbs./hour X 8760 hrs./year

= 21,900,000 lbs./year

It is easy to see that this isalso a substantial amount. Ourcalculations assume that this typeof tracing will be on year round.Not all tracing is on continuously,however. Some tracing is usedprimarily for winterizing. Thistype of tracing is for freeze pro-tection of liquid lines,instrumentation, etc. Every sec-tion of the country usually turnson this type of tracing at varioustimes, so calculations similar tothe above could be used and amodification to the amount ofhours per year should be made.

Process applications con-sume the vast majority of steam.Heat exchange equipment isused to transfer heat from steamto product, whether it is fluid orair. They are designed to con-sume all heat necessary toperform any particular task.Ideally, condensate removal fromany source should flow down-ward. In many cases this is notpractical. It is unique to heatexchangers that flow of steamand product varies and some-times it is significant.

As well as the removal ofcondensate for the monetary rea-sons mentioned previously,related to the return of hot con-densate to the boiler feedtank,

Steam Traps and the Removal of Condensate

27

there are other reasons equallyas important to why steam trapsshould be utilized, these are:

Air VentingAt start up the trap must be

capable of discharging air. Unlessair is displaced, steam cannotenter the steam space and warm-ing up becomes a lengthybusiness. Standing lossesincrease and plant efficiency falls.Separate air vents may berequired on larger or more awk-ward steam spaces, but in mostcases air in a system is dis-charged through the steam traps.Here thermostatic traps have aclear advantage over other typessince they are fully open at startup.

Float traps with inbuilt ther-mostatic air vents are especiallyuseful, while many thermody-namic traps are quite capable ofhandling moderate amounts ofair. The small bleed hole in theinverted bucket trap or the orificeplate generally leads to poor airventing capacity.

Thermal EfficiencyOnce the requirements of air

and condensate removal havebeen considered we can turn ourattention to thermal efficiency.This is often simplified into a con-sideration of how much heat isprofitably used in a given weightof steam.

On this basis the thermostat-ic trap may appear to be the bestchoice. These traps hold backcondensate until it has cooled tosomething below saturation tem-perature. Provided that the heat isgiven up in the plant itself, to thespace being heated or to theprocess, then there is a real sav-ing in steam consumption.Indeed, there is every induce-ment to discharge condensate atthe lowest possible temperature.

On the other hand, if coolcondensate is then returned to afeed tank which requires preheat-ing, the ‘efficient’ trap has donelittle for the overall efficiency ofthe steam system.

Care must also be taken inevaluating any application involv-ing a cooling leg. Drainingthrough a bimetallic steam trapmay look attractive in terms oflower temperature discharge andreduced loss of flash steam. Onthe other hand, if heat is beinglost to atmosphere through anunlagged cooling leg, then the netgain in thermal efficiency is prob-ably negligible.

Without a cooling leg con-densate will be held back withinthe plant and the main reserva-tion must be whether the plantitself will accept this waterlog-ging. It is permissible withnon-critical tracer lines or over-sized coils, but as alreadyindicated, it can be disastrous inthe case of heat exchangers.

Reliability It has been said that ‘good

steam trapping’, means theavoidance of ‘trouble’.Undoubtedly, reliability is a majorconsideration. Reliability meansthe ability to perform under theprevailing conditions with the min-imum of attention.

Given thought, the prevailingconditions can usually be predict-ed.

• Corrosion due to the conditionof the condensate or of the sur-rounding atmosphere may beknown, and can be countered byusing particular materials of con-struction.

• Waterhammer, often due to a liftafter the trap, may be overlookedat the design stage and canmean unnecessary damage tootherwise reliable steam traps.

• Dirt is another factor. A trapselected to meet all the obviouscriteria may be less reliable in asystem where water treatmentcompound carried over from theboiler, or pipe dirt, is allowed tointerfere with trap operation.

The prime requirement how-ever is the adequate removal ofair and condensate. This requiresa clear understanding of howtraps operate.

NOTE: WATERHAMMER CON-DITIONS IN A STEAM SYSTEMDAMAGE MORE THAN JUSTSTEAM TRAPS AND IS A VERYSERIOUS CONDITION WHICHSHOULD BE RESOLVED.

Steam TrapsFirst, a definition of a steam

trap may be in order to fullyunderstand the function of thispiece of equipment. A steam trapis an automatic valve designed tostop the flow of steam so thatheat energy can be transferred,and the condensate and air canbe discharged as required. If webreak this definition down intosections, it is first of all an “auto-matic valve”.

This infers that there is someform of automatic motion thatmust take place. It is “designed tostop the flow of steam so thatheat energy can be transferred”.This portion of the description issuch that it would imply the trans-mission of energy whether byflowing down a distribution pipeor giving up energy to a productin a heat exchanger. The defini-tion also continues to say“discharge condensate and air asrequired”. This portion of the defi-nition implies that some typesmay handle differing amounts ofeither condensate or air, or evena combination of the two.

In the beginning, steam trapswere manually operated valves.

Steam Traps and the Removal of Condensate

28

The major problem with this typeof condensate drainage system isthe variation to changing conden-sate flows. Condensate, you willrecall, is steam that has given upits enthalpy and reformed intowater. The amount of condensatebeing created varies in many dif-ferent ways. A fixed position of ablock valve or fixed hole in adrilled plug cock valve cannotadjust automatically to the vary-ing conditions of condensateload.

This method of condensateremoval would warrant an opera-tor be present much of the time tocorrect the setting of the valve. Ifcondensate was allowed to backup, less heat transfer would takeplace, causing production to falloff. If, on the other hand, thecondensing load was less, theoperator would have to close thevalve to the point that steam wasnot continuously being released.Because of the changing natureof condensing loads, this wouldbe a full-time job.

True steam trap operation willfall under one of the followingthree categories:

1. Mechanical or Density

2. Thermostatic or TemperatureControlled

3. Thermodynamic or Velocity

These categories of trapshave distinctive operating charac-teristics and work most efficientlywhen used for their designed pur-pose. It would stand to reasonthat steam traps evolved withindustry and demand. There arereally only three applications forsteam traps: drip stations (locat-ed on steam delivery lines),tracing (steam lines designed tomaintain a product temperatureor keep a liquid system fromfreezing) and process (steamused specifically for heating prod-ucts such as air, process fluids,

foods etc.). These differing appli-cations will be discussed later.Our purpose now is to explore theoperating characteristics of trapsand where they fall within eachcategory.

Mechanical Steam TrapsThere are two basic designs

of steam traps in this category.They are the “Float andThermostatic” and the “InvertedBucket” designs. The float andthermostatic design evolved pri-marily from a free floating balldesign.

The first float type trap con-sisted of a free floating ball in anexpanded area of pipe. It was atop in, bottom out type of systemthat required water to fill theexpanded area and float the ballupwards, exposing the outlet pip-ing and outlet orifice. As long ascondensate was flowing to thetrap, condensate would flow fromthe trap at the same rate. Thefloats were weighted slightly torequire water to always be pre-sent in the trap and thereby stopsteam from leaking into the con-densate return line or toatmosphere. It was soon noted,however, that air would accumu-late in the expanded area of pipeand form a bubble which keptcondensate from flowing down-ward. A piece of pipe was addedto the inlet piping to the trap anda manual valve attached to beperiodically “blown down” to keepwater flowing to the trap and airremoved. When the thermostaticbellows steam trap was invented,it soon took the place of the man-ual valve and automated theprocedure.

Float And Thermostatic TrapModern Float and Thermo-

static traps (Fig. 21) still have aball type float, but it is nowattached to a lever. The lever is

attached to a valve head andpivot point. When condensateenters the trap, the float rises withthe liquid level and mechanicallypulls the valve off the seat toallow condensate to be dis-charged. A thermostaticallyoperated air vent is still presentbut located inside the body onmost modern day designs of F&Ttraps.

Some manufacturers locatethe “air vent” externally, but thepurpose is the same. This part ofthe trap is strictly there forautomating the air venting proce-dure. It is also noteworthy to notehere that this type of trap has onebasic application point, and that isfor process purposes. This is dueto the fact that this trap typeimmediately removes air andnon-condensables as they enterthe trap and discharges conden-sate in the same manner, atsaturation temperatures. Theremay be some limited uses otherthan process for this type of trap,but primarily it is used in this typeof application.

The main advantages to thistype of trap is its superior airremoval capabilities either onstart up or during the processprocedure. It also has a continu-ous discharge characteristic thatfollows exactly the forming of con-densate. In other words, whatcomes in goes out at the samerate. This type of steam trapadjusts automatically to eitherheavy or light loads of condens-ing and is not adversely affectedby changes in pressure.Condensate removal is also doneat steam temperature, so heatexchange takes place at constanttemperatures, insuring maximumefficiency use of the energy sup-ply.

Steam Traps and the Removal of Condensate

29

A disadvantage is general toall mechanical type of traps andthat is the power of the float isconstant, so as steam pressuregoes up, the size of the permissi-ble discharge orifice goes down.In practice, mechanical trapsmust have different sizes ofvalves and seats for differentpressure ranges. This is toensure that the float and levercombination has the ability togenerate enough energy to lift thevalve head off of the seat at thedesign operating pressures. If itcannot, the trap mechanism isovercome by the steam pressureand the trap fails closed.

Inverted Bucket TrapsThe second mechanically

operated steam trap is theInverted Bucket type of trap (Fig.22). In this trap, the operatingforce is provided by steam enter-ing and being contained within aninverted bucket causing it to floatin condensate that surrounds thebucket itself. The bucket isattached to a lever and pivot pointsimilar to that in the F & T. Thevalve head and seat, however,are located at the top of the trap.It requires water being presentwithin the body in order for thebucket to have something inwhich to float. This is called the“prime”.

When steam is first turnedon, air is allowed to flow to thetrap. This air is captured withinthe bucket and flows out througha hole in the top of the bucketknown as the “vent hole”. Airpasses upward through the hole,through the prime, and collects atthe top of the trap. Since the sys-tem is building pressure, the air isat its most compressed state.This puts a downward force onthe prime and pushes it back upinto the bucket. As this bucketfills with water, it loses buoyancy

Figure 21Float and Thermostatic Steam Trap

Figure 22Inverted Bucket Trap

Thermostatic Air Vent

Steam Traps and the Removal of Condensate

30

and sinks in the surrounding liq-uid. In doing so, it pulls the valvehead off of the valve seat andallows the collected air to dis-charge. Flow from under thebucket starts again. This allowseither more air or steam to beginto enter the trap body. If it is moreair, the sequence is repeated.

If it is steam, however, thesequence is different. Steampasses through the bucket venthole to the top of the trap and iscondensed by heat losses fromthe trap body, in particular the capor top. This loss is necessary tokeep steam and condensatecoming to the trap. As conden-sate enters under the bucket, itfills the space and again thebucket loses buoyancy and sinks.Discharge flow is first downwardfrom under the bucket, and thenupward to the discharge orifice.

The biggest advantage to thistype of trap is its ability to with-stand high pressures. It has areasonable degree of tolerance towaterhammer damage but suffersfrom freeze damage. In the caseof freezing, however, most of thedamage is done to the body ofthe trap rather than to the mecha-nism or float.

The disadvantage to thistrap type is its limited ability todischarge air and other non-con-densable gases. This is due tothe small vent hole and low differ-ential pressure driving the airthrough it. It is suspect at times torapid pressure changes in thesystem due to the requirement ofa “prime” being maintained inter-nally for proper operation. The“prime” water seal is at saturatedsteam pressure/temperaturesand if the steam pressure dropsrapidly due to load changes ofequipment, the “prime” has a ten-dency to boil off (flash). Withoutthe required “prime,” this type oftrap fails open.

This type of trap is mostappropriately suited for stable,steady load and pressure condi-tions such as one would find on asteam distribution system.

Thermostatically or Tempera-ture Controlled Traps

The balanced pressure orbellows type of steam trap wasfirst manufactured with a bellowsof copper design. This bellows(Fig. 23) had a liquid fill which, inthe beginning, was distilled water.Modern thermostatic type trapsstill have a liquid fill but it is madeup of a distilled water and alcoholmixture and they are containedwithin an enclosed capsule ratherthan a bellows. Alcohol wasadded to the fill to lower its boilingpoint.

The capsules work by exploit-ing the difference in the boilingpoint between the alcohol mixtureand the surrounding condensate.As the temperature of the con-densate gets closer to steamtemperature, the mixture con-tained within the capsule getscloser to its boiling point at a settemperature below that of steam(before steam reaches the trap),the mixture evaporates. Thisresults in an increase in internal

pressure of the capsule, which isgreater than that within the trapbody so forcing the valve downonto its seat, and preventing thetrap from blowing steam. As thesteam condenses back to con-densate, and the temperaturedrops accordingly, the alcoholmixture recondenses so relievingthe internal pressure of the cap-sule and thus lifting the valveback off its seat, allowing conden-sate to flow through the trap.

The mixture of distilled waterand alcohol in the bellows is thekey to the operating temperaturesof the balanced pressure trap.Most manufacturers provide ther-mostatic traps to operate within20 to 40 degrees of saturatedsteam temperatures. An impor-tant point to remember is that allthermostatically operated steamtraps will cause condensate toback up in the system. Theamount of backup in the systemis dependent upon the tempera-ture that the trap is designed tooperate at, along with the con-densate loads coming to the trap.

The advantage to this type oftrap is its ability to freely and

Figure 23Stainless Steel Bellows for Thermostatic Trap

Steam Traps and the Removal of Condensate

31

immediately discharge air andnon-condensables as soon asthey enter the trap’s body, as inthe F & T. These traps have theability to operate up to 600 PSIGand provide constant and consis-tent levels of subcooling of thecondensate in relation to the sat-urated steam pressure/tempera-ture curve. The most moderndesigns have overcome the earli-er models’ sensitivities ofwaterhammer and superheatdamage by encapsulating the fill-ing in a much more robustenclosure.

The disadvantages of ther-mostatically operated traps is thatthere is always a backup of con-densate in the system, whichcould reduce heat transfer insome applications. These trapsalso will require a time period toadjust to load changes in the sys-tem. Balanced pressure steamtraps are used very commonly inair venting, distribution, main dripdrainage and in tracing applica-tions.

Figure 24Bimetallic Trap

Bimetallic Thermostatic TrapsBimetallic type traps have

shown a lot of variation sincetheir original design. The moderntypes of bimetal traps all are com-mon in that the valve is locatedon the outlet side of the trap andthe bimetal strips, or disks, arelocated inside the body. Thismeans that the action of the trapis to pull the valve head into thevalve seat opposing the steampressure of the system, trying todrive the valve head off of thevalve seat.

The bimetal strips or disks (Fig.24) are made of two dissimilarmetals, usually of 304 and 316stainless steel. Because they aredissimilar metals, one expandsmore than the other at a giventemperature. It is said to have dif-ferent coefficients of expansion. A

characteristic of this differingexpansion rate is that the elementhas to bend or arch. This bendingmotion can then be used to openor close a valve accordingly.

This type of trap has a verydeep subcooling range. Thisrange may be as much as 100°Fbelow the saturation tempera-tures, thus causing excessiveback up of condensate into thesystem. Extreme caution must betaken when applying a bimetalthermostatic trap to equipment soas not to cause equipment dam-age from this backup ofcondensate.

The advantages to this typeof trap are its ability to withstandwaterhammer and handle fairlylarge condensate loads for itssmall physical size. They do dis-charge air and non-condensablegases well, but because of theirlow temperature sensitivity (sub-cooling), they may fully closebefore all of these gases areremoved. The trap drains freelyupon drop in temperature or sys-tem shutdown, so freeze damageshould not be a factor. Its prima-ry use is for drip stations onsuperheated steam mains, wheresuperheated steam and conden-

sate cannot coexist. Anotherapplication in which these areused is for non-critical tracing(freeze protection) where energyefficiency is maximized.

A disadvantage to this type oftrap is the lag time required whencondensate loads change toopen the trap. Response tochanges are very slow. Anotherdisadvantage to this type of trapis that they are highly susceptibleto dirt being caught between thevalve head and seat. Also, dirtattaches to the bimetal strips ordisks and acts as and insulator,changing the discharge charac-teristics.

Valve Open

Steam Traps and the Removal of Condensate

32

Liquid Expansion Thermostat-ic

This type of trap is a variationto the standard thermostaticsteam trap. The variation comesin the fill which is used and thelocation of that fill. There is a bel-lows but it is surrounded by a lightmineral oil (Fig. 25). Another vari-ation on this type of trap is anadjustment nut which allowsadjustment of the stroke on thevalve. The operational character-istics remain much the same asfor the bellows type trap.

On start-up, the bellows isrelaxed and the valve is wideopen. Air is allowed to pass freelythrough and out of the trap. Ascondensate begins to flow to thetrap, it surrounds the bellows andflows out as well. As the conden-sate temperature rises, ittransfers its heat energy into themineral oil filling which causesthe mineral oil to begin changingits volume (expanding). Thechanging volume of the mineraloil exerts a force on the end of thebellows and forces a plungervalve toward the seat. This traptype has a substantial subcoolingrange. This range is variable andadjustable with the mineral oilwhich makes up this type of trap.It will back up condensate andregulate its flow by its tempera-ture. Since the dischargetemperature of this type of trap isadjustable, it is best used where

inexpensive temperature controlis needed. A primary applicationfor this type of trap is on hot wateror oil storage tanks where thetemperature of the stored liquidsneeds to be kept below steamtemperature of 0 PSIG (212°F).

The main advantage to thistype of steam trap is its ability toadjust a discharge temperature tomatch that desired in the storagetank. This effectively reducessteam consumption on applica-tions where controlledwaterlogging can be tolerated.This trap can and is used also forfreeze protection of float andthermostatic steam traps.

The major disadvantages tothis trap are the amount of con-densate back-up plus its inabilityto respond rapidly to condensateload changes and its sensitivity todirt.

Thermodynamic Steam TrapsThis type of steam trap uses

velocity to open and close avalve. The valve in this type oftrap is a free floating disk whichsits on two seating surface areas.One area is an inlet orifice andthe other are multiple outlet ori-fices located in an adjacent ring.It is a fairly simple trap to under-stand. On start-up, the disk isforced upward and off the seatingsurface rings by the flow of airand condensate. Condensateand air are discharged from the

Figure 25Liquid Expansion Thermostatic Trap

trap. Condensate force is direct-ed to the center and under thedisk chamber and is exposed tothe outlet ring of orifices. It rec-ognizes a lower downstreampressure within the chamber andflashing of the condensateoccurs.

Flashing is nature’s way ofcooling condensate back to thesaturation temperature at which itcan exist as liquid at the lowerpressure. The excess heat ener-gy in the condensate that cannotexist as liquid at the lower pres-sure and temperature generatessteam at the lower pressure andexpands. This expansion causesan increase in the velocity of flowbetween the bottom of the diskand the seating surfaces, whichin turn causes a negative pres-sure to be sensed on the bottomof the disk beginning to pull itdown onto the seating surfaces.Some of the flash steam that isbeing created flows around thesides of the disk to the top sur-face of the disk. This flash steamis trapped between the top of thedisk and the cap of the trap andpressure develops in this space,pushing the disk down onto theseating surfaces.

When the pressure in the capchamber is great enough to over-come the inlet pressure of thecondensate on the bottom of thedisk, the trap snaps closed. The

Steam Traps and the Removal of Condensate

33

trap will remain closed until thepressure in the cap chamber hasdropped to below the inlet pres-sure. Then the cycle will repeatitself. The cap chamber pressuredrops due to natural heat lossesfrom the cap to the ambient con-ditions, condensing this steam.This type of trap operates on acyclical pattern, either open orclosed. Because the trap isclosed by flash steam createdfrom hot condensate, there is asmall amount of subcooling of thecondensate and back up of con-densate in the system. Thesubcooling ranges between 2 to10°F below saturated steampressure and temperature rela-tionship.

The advantages of this typeof trap are they are not damagedby waterhammer or freezing andwill work consistently throughouttheir pressure range (up to 1750PSIG). They can be utilized onsuperheated steam systems with-out any problems, and they areeasily tested, installed and main-tained. This is the only type ofsteam trap that will give an indi-cation of wear before final failureoccurs. The cycling rate increas-es with wear and gives a distinct

Figure 26Thermodynamic Steam Trap

ConclusionThe three catagories of

steam traps discussed above arethe most commonly used andwidely known trap types. Thereare obviously variations to almostall of the traps described in thissection. Some of those variationscan be seen in the followingdescriptions and operating char-acteristics.

Variations on Steam TrapsIf we begin reviewing some of

the variations of steam traps inthe mechanical grouping, we notefirst the float type trap (Fig. 27).This type of design operatesmore like a liquid drain type trapthat has no real balance line. Youwill see a small petcock valvelocated on top of the trap. Thisvalve would be left open slightlyto allow air and other non-con-densables to be discharged. Itprobably worked fairly well for itsday, but in today’s world of expen-sive steam, would not beacceptable. Even a small steambypass or leak may cost hun-dreds of dollars per year.

Figure 27Float Trap

audible clicking sound (rapidcycling).

The disadvantages to thistrap are that it does not operatewell at extremely low pressures(below 3.5 PSIG) or extremelyhigh percentages of back pres-sure (around 80%). They arealso limited in their air handlingcapability.

This type trap is ideally suitedfor steam main distributiondrainage and tracing applica-tions.

Air Vent

Steam Traps and the Removal of Condensate

34

In the Thermostatic categoryof traps we see the most activityin attempts to redesign some ofthe elements themselves. In thebeginning, you may rememberthat a balanced pressure bellowstype of trap was originally madeof copper. Bellows still exist todaybut are now made of stainlesssteel. This allows the manufac-turers to use a more robust

material and also allow them touse welds on the edges of disksfor more strength (Fig. 30). Thedisks have a hole in the center toallow a hollow space to be creat-ed when they are weldedtogether. This creates a bellowsfor fill just like the extruded cop-per bellows. It is said that thesebellows are filled under vacuum,but in reality they are just com-

Figure 28Free Float Trap

Figure 29Open Top Bucket Trap

Another variation to the Floatand Thermostatic trap is a freefloating ball (Fig. 28) with theaddition of a bimetal disk locatedat the top of the trap for air vent-ing purposes. The outlet orifice islocated on the lower section ofthe trap. The idea behind thistype of trap valve and seat isbasically the same as the ancientdesign of the original float typetrap. The one big difference isthat the seat is extended slightlyoutward from its position insidethe trap body. This extensionwould cause dents to be createdon the ball float that would notallow it to properly seat off whenit was required. Another specialnote of attention should be paidto the operating (closing andopening) temperature of thebimetal disk for air venting pur-poses. The disk is a bimetaldesign that may close premature-ly and not allow for proper airventing to take place. It may notopen again until the subcoolingrange allows it to do so and airbind the trap. A special screwedstem is installed on the trap top toallow an operator to force thebimetal disk off the seat andagain allow some steam to passto prevent air binding of the trap.

The upright bucket trap (Fig.29) uses siphon and float opera-tion. As you can see by thedesign, the upright bucket allowscondensate to flow over the floatand fill from the top. This weighsdown the bucket to the point thatit sinks in the surrounding fluid.As it sinks, the valve is pulled outof the seat and line pressureforces the condensate inside thebucket to flow. It is fairly obviousthat this type of design wouldhave a lot of difficulty in riddingitself of air. Air binding was amain source of problem for thistrap.

Steam Traps and the Removal of Condensate

35

pressed when filled and sealed.

The problem with having aliquid fill on the inside of a bellowsstill exists. That problem beingthe fill over expanding and ruptur-ing the bellows when a smallamount of superheat may beallowed to reach the trap inter-nals. There have been twoattempts to try to correct for this.As mentioned earlier, thermostat-ic type traps usually (but notalways) reach a point where theinside pressure balances to theoutside pressure of the bellows.This causes them to basicallyaverage the pressure tempera-ture and constantly dribble. Oneattempt to solve the over expan-sion problem and dribbledischarge was to create a singlewafer type of capsule where thecenter portion containing thevalve was forced in during the fill-ing procedure of manufacturing.This created a bowing type ofappearance and caused the cap-sule to operate more like thebottom of an oil can. As the fillvaporized it “popped” the portionof the capsule outward andforced the valve head on to theseat. As the fill cooled and con-

Figure 30Balanced Pressure Capsule

for Thermostatic Trap

tracted it popped again to theoriginal position and opened thevalve to allow discharge. Thispopping action meant that itwould insure the trapping of somecondensate around the capsuleat all times and prevent overexpansion. Superheat has nocondensate, as you know, andalso has a tendency of vaporizingany condensate in a system onceit is up to full temperature. Thisstill created over expansion, butthe trap now had a more distincton and off type of operation whenused on saturated steam lines.

The problem with this type oftrap was the design and locationof the liquid fill that causes thetrap to operate. Later design ofthe capsule put the liquid fill onthe outside of the moving part ofthe wafer. The result of the fillvaporizing and forcing the valveto the seat in part then doublesthe thickness of the wafer at itsweakest point. It is also apparentthat the fill then be encased in athicker shell to prevent waterhammer damage to the element.As you can see, the operation ofthis type of design improvementfor the thermostatic trap is much

more resistant to damage byeither superheat or water ham-mer.

There have been manydesign changes over the evolu-tion of the bimetal type of steamtrap. They started off by the stripof metal expanding and pushingthe valve into the seat. The obvi-ous problem with that wasaligning the valve head to theseat. Then it evolved to pull thevalve into the seat (Fig. 31). Ineither case though, a single stripof very heavy metal could onlycreate a linear tracking of thesteam curve. Close inspection ofthis shows that the deepest sub-cooling range occurred at aboutthe highest point in the steamcurve. This meant that there wasa lot of condensate backed upinto the lines. A point to remem-ber is that these traps can beadjusted by adjustment nuts onthe stem. This controls the valvestem stroke and discharge tem-perature.

The next step in evolutionwas to “stack” strips that were ofdifferent thickness to both addpower to draw on the valve stemand also operate at differing lev-

Figure 31Simple Bimetallic Trap

Steam Traps and the Removal of Condensate

36

Figure 32Impulse Trap

els of the steam curve. Thischange, as can be seen in thecurve, creates the effect of bend-ing the straight line discharge ofsingle metal strips. It follows thesteam curve closer than just asingle heavy metal strip. Thismade the trap more acceptablefor use on some saturated steamlines but still kept a problem thatexists with the design. This prob-lem is how to draw a straightvalve stem up through an outletorifice with a arched draw.Typically, these two designs bindthe valve stem within the orificeitself and can cause it to hang upand continuously leak.

As this trap was developed, itneeded to maintain: A) closingforce, B) operation to steamcurve, and C) valve steam posi-tion through trap orifice. As youcan see by this newer design, thediffering lengths of bimetal stripswould follow the steam curveadding force as the temperatureand pressure rises. Also, the holethrough the center allowed themanufacturer to create a straightpull on the valve stem to draw thevalve directly through the centerof the orifice. The second exam-ple of this type of new designstacked disks of bimetals oppos-ing each other on the stem whichresults in the same type of actionas the newer cross design. Itshould be mentioned that the jobof the steam trap is to removecondensate which these designswill do, but should do so withregard to subcooling temperatureof operation. All designs offer theadjustability of the stem stroke,but time is required to set themproperly. With all of the down siz-ing of plants today, this probablydoes not occur that often.

Thermodynamic traps areeither of the flat disk design dis-cussed earlier or of the piston

design. The piston design (Fig.32) as you can see, incorporatesa constant bleed hole through thepiston stem and seating disk.This relieves the pressure aboveand allows the disk to open to dis-charge. This hole is very smalland easily plugged rendering itineffective. Other design differ-ences in TD traps is location andsizes of outlet orifices. Sometypes use two different sized ori-fices located on opposite sides ofthe trap and in line with the pip-ing. This causes the disk tooperate in a tilting fashion ratherthan straight up and down as withthe three symmetrically spacedand same sized orifices. The tilt-ing action causes the disk to spinduring the closing sequence andcause wear on the outside edgeof the seating surface and diskitself. Wear on this type of trapshould be kept as even as possi-ble to prolong the life expectancy.Another variation to disk traps isthe inlet flow directions. Some

traps are designed to flow thecondensate and steam over thecontrol chamber and create abarrier to ambient conditions. Inorder for the trap to work if sur-rounded by steam or hotcondensate, a groove is cut intothe disk that crosses the seatingsurface to bleed the steam fromthe top of the disk when closed.In this case, the trap uses steamas the gas to force closure of thetrap and not flash to do the work.

With all of the types of trapsand variations to each, how doesone effectively choose a trap forapplication to their specific plantuse? The following chart, “SteamTrap Selection Guide” (Fig. 34),may help in the selectionprocess. You must first determinethe factors required from yourown plant size and age. You mustdetermine the needs for conden-sate and air removal.

Steam Traps and the Removal of Condensate

37

Steam Trap Testing MethodsThere is virtually no point in

spending the time and money increating a highly efficient steamsystem and then failing to main-tain it at this same level.However, all too often leakingjoints and valve stems areaccepted as a normal operatingcondition of both steam and con-densate systems.

Even a 1/8" diameter holecan discharge as much as 65lb/hr of steam at 150 PSIG whichrepresents a waste of approxi-mately 30 tons of coal, 4,800gallons of fuel oil or 7,500 thermsof natural gas in a year (8400hours).

Elimination of the visibleleaks already mentioned is obvi-ously reasonably straight forward.It is the invisible steam leaksthrough faulty steam traps thatpresent a far more taxing prob-lem. We know that the basicfunction of a steam trap is to dis-charge condensate andnon-condensable gases in oursystems and prevent live steamfrom escaping. Steam trap testinghas brought about four differentmethods of testing. Let’s look atall four methods and see whateach will tell us about the condi-tion of the steam trap.

Visual TestingThe first point that has to be

understood when visually testinga steam trap is that it will be avery rare occasion where the onlymatter coming out of a steam trapwill be water!! Almost always,there will be varying mixtures offlash steam and water and insome cases the visual dischargewill be all flash steam. So the firstthing to remember is that we donot want to look for water only,nor do we want to attempt todecide if we are seeing the

appropriate amount of flashsteam and water mixture.

Visual testing of steam trapsworks best on two types of trapoperation due to the trap’s inher-ent discharge characteristics.Those two traps are the InvertedBucket (Density) andThermodynamic (Kinetic Energy).These two traps operate in acyclical manner being fully open,discharging, or fully closed. Theopen/closed operation is the keyto correct visual testing and whatthe tester should be looking for toindicate a properly operatingsteam trap.

If there is installed in the pip-ing ahead of the steam trap a wye(“Y”) strainer with a blowdownvalve, opening the blowdownvalve and diverting all of the con-densate away from the steamtrap allows only steam into thetrap.

Any steam trap type shouldclose positively when it sensesonly steam. This additional step,diverting the condensate awayfrom the trap’s inlet, allows thetester to test any type of trapoperation and receive 100% pos-itive answers to the trap’scondition.

Ultrasonic Trap TestingUltrasonic trap testing began

with a screwdriver and has pro-gressed to electronic sensingdevices which amplify vibrationsof flow. Flow of water and steamset up vibrations which are whatwe are looking for with ultrasonictesting. This form of testingworks very well on traps that havecyclical discharge characteristics,like the kinetic energyThermodynamic and the densityoperated Inverted Bucket. Theopen/closed operation provides avery positive answer to the trap’soperation.

When testing other traps, likeFloat & Thermostatic andThermostatic types which providecontinuous modulating discharge,the tester again has to open thestrainer blowdown valve anddivert condensate away from thetrap inlet so that the trap seesonly steam. Again, if it is a prop-erly operating trap, it will shut offcompletely. The ultrasonic testingdevice must be calibrated to elim-inate external piping noises orother steam traps’ discharge.When testing traps that are inclose proximity, all traps exceptthe one being tested must be iso-lated to remove any false signalsfrom the other traps.

The ultrasonic testing methodcan provide very positive answersto a trap’s operating condition aslong as the operator doing thetest has been trained, has devel-oped some experience with thetesting instrument and is able toidentify the type of trap operationby visual inspection.

Temperature TestingTemperature testing of traps

involves measuring the tempera-ture at, or close to, the inlet andoutlet of the steam trap.Pyrometers, temperature sensi-tive crayons, paint, band-aids andthermocouples all have theiradvocates. Unfortunately, thesemethods are of limited use sincethe temperatures of condensateand flash steam on the down-stream side of a correctly workingsteam trap are controlled by thepressure in the condensatereturn system. A very large per-centage of steam traps in theUSA are thought to dischargeinto “0” PSIG, atmospheric gravi-ty returns, which means that themaximum temperature that couldbe expected is 212°F, regardlessof the trap’s operating condition.

Steam Traps and the Removal of Condensate

38

It does not necessarily mean thata trap has failed when an elevat-ed temperature above 212°F isrecorded downstream of a steamtrap. More likely it means that thecondensate return line is under apositive pressure, which meansthat the pressure/temperaturerelationship of steam must exist.

Thus if we were to record atemperature of 227°F on the out-let side of a trap, this tells thetester that the return system is at5 PSIG saturated steam condi-tions, even though it was thoughtto be a “0” PSIG return system.There could be a failed opensteam trap in the system that iscausing this pressure or it couldbe purely the fact that the con-densate return line was sized forwater only and is not able toaccommodate the flash steamvolume without becoming pres-surized. Temperature testing willidentify a “failed closed” steamtrap due to very low temperaturesat the inlet of the steam trap.Temperature testing of traps to

Figure 33Conductivity Trap Testing System

find failed open traps is by far theleast accurate of all the testingmethods available to users.

Conductivity TestingA more recent development

in trap testing uses the electricalconductivity of condensate. Thisinvolves the installation of achamber (Fig. 33) containing aninverted weir upstream of thesteam trap shown as follows.

With the trap working normal-ly, condensate flows under thisweir and out through the trap.There is a small hole at the top ofthe weir that equalizes the pres-sure on each side. A sensor isinserted in the chamber on theupstream side which detects thepresence of condensate by com-pleting an electrical circuit withthe condensate. A portable indi-cator is plugged into the sensorand the indicator provides theability to read a completed circuiton the sensor. If the trapbecomes defective and beginsblowing steam, equilibrium on

Steam Trap

Live Steam

Red & Green Lights

Red Light:Trap Passing Live Steam

Green Light:Trap Working Correctly

Type 30 Indicator

SensorChamberHole

Weir

Condensate

either side of the weir becomesdisturbed and the steam pressureon the inlet side of the chamberdisplaces the condensate belowthe sensor. The sensor is nolonger surrounded by the conduc-tive condensate and the electricalcircuit is broken, providing a failedsignal on the indicator.

A major advantage to thismethod is the very positive signalwhich can be interpreted withoutresorting to experience or per-sonal judgment. It is possible towire a number of sensor cham-bers to one remote testing pointfor ease of quickly testing largernumbers of traps. The latestdesigns of conductivity testingequipment have added a temper-ature sensor in the samechamber that will provide the abil-ity to determine a failed closedtrap.

Steam Traps and the Removal of Condensate

39

By-Passes Around SteamTraps

The habitual use of by-passvalves around steam traps canresult in significant waste andloss of steam energy. Although aby-pass can be a very usefulemergency device, it shouldnever be regarded as a normalmeans of discharging conden-sate or air. Some trapping pointsstill incorporate by-passes due tothe misguided belief that they areessential to cope with start-upconditions. The operator mayalso be tempted to leave the by-passes cracked open duringnormal running. A valve used inthis way will rapidly become wire-drawn and incapable of giving atight shut-off. Once this hasoccurred, greater steam lossesare inevitable. Steam traps arefully automatic devices whichshould be properly sized so thatby-passes are unnecessary.

Preventive Maintenance Pro-grams

In order to ensure that pres-sure reducing valves, tempera-ture controls, steam traps, etc.give long life and trouble-free ser-vice, it is essential to carry out aprogram of planned preventivemaintenance. In general, this willmean regular cleaning of strainerscreens and replacement of anyinternals which are beginning toshow signs of wear. It is alwaysadvisable to hold a stock ofspares recommended by the rele-vant manufacturer and a numberof standby valves and traps whichare on hand for use in an emer-gency.

Most steam system mainte-nance will have to be carried outduring an annual shutdown, but itis usually easier to spread thework evenly over the course of anentire year. Most items will onlyneed attention once every twelve

months, although strainerscreens may need more frequentcleaning, especially in the case ofnewly installed systems. In con-clusion, it may be useful to listsome of the causes of problemscommonly experienced with thevarious patterns of steam trapswhich are available.

Steam Trap Fault FindingThermodynamic Disc Trap

Symptom-Trap Blows Steam

The trap will probably give aseries of abrupt discharges(machine gunning). Check fordirt, including the strainer, andwipe the disc and seat. If noimprovement, it is probable thatthe seating face and disc havebecome worn. The extent of thiswear is evident by the normalcrosshatching of machining. Thiscan be dealt with by:

1. Re-lapping the seating faceand disc in accordance withthe manufacturer’s instruc-tions.

2. Installing a new disc if thetrap seat is in good condition.

3. If both seating face and discare not repairable, then thecomplete trap must bereplaced.

If historical records show thatthermodynamic traps on one par-ticular application sufferrepeatedly from rapid wear, sus-pect either an oversized trap,undersized associated pipe workor excessive back pressure.

Symptom-Trap will not passcondensate

While the trap’s dischargeorifices may be plugged shut withdirt, this symptom is most likelydue to air binding, particularly if itoccurs regularly during start up.Look at the air venting require-ments of the steam usingequipment in general.

Balanced PressureThermostatic Trap

Symptom-Trap blows steam

Isolate the trap and allow it tocool before inspecting for dirt. Ifthe seat is wire-drawn, replace allthe internals including the ther-mostatic element. The originalhas probably been strained bythe continuous steam blow. If thevalve and seat seem to be ingood order, then check the ele-ment. To check the elementremove the complete elementand holder assembly from thetrap. Place the complete assem-bly in a pan of boiling water belowthe water level in the pan with thedischarge end pointing up. Leavethe assembly submerged in theboiling water for 5 minutes thencarefully lift the assembly out ofthe water, as the element isremoved from the water thereshould be a water accumulationin the discharge of the element.Set the element assembly on atable, still with the discharge endup and observe the water in thedischarge side of the element. Ifthe element is working correctly,the water will remain in the dis-charge until the element coolsthen the water will drain out ontothe table. If the element hasfailed, the water will leak out ofthe immediately.

Symptom-Trap will not passcondensate

The element may be over-extended due to excessiveinternal pressure making itimpossible for the valve to lift offits seat. An over-expanded ele-ment could be caused by superheat, or perhaps by someoneopening the trap while the ele-ment was still very hot, so that theliquid fill boiled as the pressure inthe body was released.

Steam Traps and the Removal of Condensate

40

Liquid ExpansionThermostatic Trap

Symptom-Trap blows steam

Check for dirt or wear on thevalve and seat. If wear hasoccurred, change the completeset of internals. It must beremembered that this type of trapis adjustable in the temperatureof discharge, check to see if inad-vertently the trap’s adjustmenthas been turned out too far for itto close. Try adjusting the trap toa cooler setting. If it does notappear to react to temperature, acomplete new set of internalsshould be fitted.

Symptom-Trap will not passcondensate

Check that the trap’s adjust-ment has not been turned in toofar to a setting that’s too cold.

Bimetallic Thermostatic TrapSymptom-Trap blows steam

Check as usual for dirt andwear on the valve and seat. Abimetallic trap has only limitedpower to close by virtue of itsmethod of operation and thevalve may be held off its seat byan accumulation of quite softdeposits. This type of trap is usu-ally supplied pre-set to a specificamount of subcooling. Check tosee that the locking device on themanual adjustment is still secure.If this seems suspect, see if thetrap will respond to adjustment. Ifcleaning has no effect, a com-plete new set of internals shouldbe installed.

Symptom-Trap will not passcondensate

Bimetallic traps have thevalve on the downstream side ofthe valve orifice which means thatthey tend to fail in the open posi-tion. Failure to pass coldcondensate indicates either grossmis-adjustment or complete

blockage of the valve orifice orbuilt in strainer.

Float & Thermostatic TrapSymptom-Trap blows steam

Check the trap for dirt foulingeither the main valve and seat orthe thermostatic air vent valveand seat. If a steam lock releaseis installed in the trap, check toinsure that it is not open causinga leak. Make sure that the floatand valve mechanism has notbeen knocked out of line either byrough handling or waterhammer,preventing the valve from seating.Check that the float ball has notbeen damaged by waterhammerand developed a leak whichwould not allow the float ball tofloat or bind in its operation. Theair vent assembly should be test-ed in the same manner as theBalanced Pressure Thermostatictrap element. When replacing themain float mechanism and valveassembly, these should bereplaced as a complete set.

Symptom-Trap will not passcondensate

Check that the maximumoperating pressure rating of thetrap mechanism has not beenexceeded. If this has happened,the mechanism will not have thepower to open the valve againstthe higher steam pressure. Aleaking or damaged float isalmost certainly the result ofwaterhammer damage and theproblem should be corrected.

Inverted Bucket TrapSymptom-Trap blows steam

Check for loss of the waterseal “prime”. Isolate the trap, waitfor condensate to accumulateand start up the trap again. If thiscures the trouble, try to discoverthe cause of the loss of the waterseal “prime”. This could be due tosuperheat, sudden pressure fluc-

tuations or the trap being installedin such a way that the water sealcan drain out by gravity. Try fittinga check valve before the trap toprevent this loss.

If steam blow persists, checkfor dirt or wear on the valve headand seat or failed mechanism.Replace the complete valvemechanism and linkage as acomplete set.

Check the bucket to deter-mine if it is distorted fromwaterhammer.

Symptom-Trap will not passcondensate

Check that the maximumoperating pressure of the mecha-nism has not been exceededcausing the trap to lock shut.While checking the internals,insure that the air vent hole in thebucket is not obstructed, as thiscould cause the trap to failclosed. Air venting could also bea cause of a failed closed trap,especially in systems that start upand shut down frequently. Lookat the air venting arrangements ofthe steam using equipment ingeneral.

ConclusionIt is important to know the

type of trap discharge (Fig. 34)which should be expected whenmaking maintenance checks ortrap testing. The table on the fol-lowing page sets out the usualdischarge characteristics of themost commonly used traps.TRAP TYPE

Steam Traps and the Removal of Condensate

41

Figure 34Steam Trap Discharge Characteristics

Steam Trap SelectionIt can be claimed that the

majority of steam trap types will“work” on any application (provid-ed that the operating conditionsfall within the pressure range andcondensate discharge capacity ofthe trap) (Fig. 35). However, wedo not just want steam traps to“work” moderately well. We mustaim to achieve maximum outputand efficiency from all steamusing equipment. This meansselecting the best trap to suiteach particular application (Fig.36).

The following list contains anumber of important questionswhich should be consideredwhen choosing a steam trap for aparticular application:

1. Will condensate be dis-charged immediately as itforms?

2. Is there condensate backpressure or a return line high-er than the steam heatedequipment?

3. Are there waterhammer con-ditions in the steam supplyline?

4. Is there vibration or exces-sive movement in theequipment?

5. Does the condensate containcorrosive substances?

6. Will the trap be in an exposedposition?

7. Is the steam supply superheated?

8. Is air likely to be present in any quantity?

9. Is steam locking a possibili-ty?

10. Is the installation made up of several steam heated units?

WaterloggingWith most steam heated

equipment it is desirable, andvery frequently essential, to dis-charge condensate as soon as itforms in the steam space.Although sensible heat in thecondensate is usable heat, amuch greater rate of heat transferwill be obtained if only the steamis in contact with the heat transfersurface.

Steam traps of the mechani-cal type should always be chosenfor applications which requirerapid condensate removal.Thermostatic type traps cannotrelease condensate until it hascooled a set number of degreesbelow steam temperature, result-ing in waterlogging the steamspace. There are, however, anumber of occasions when suchwaterlogging may be perfectlyacceptable and even desirable.

As an example, let us consid-er the difference in trappingrequirements of a steam radiatorand a unit heater. While thesteam space of the radiator isgreat compared with its heatingsurface, the steam capacity of theunit heater is small comparedwith its heat output. The radiatorcan make good use of the sensi-ble heat in the condensate beforeit is discharged, but the unitheater cannot. For this reason,the radiator should be fitted with athermostatic trap that will holdback condensate until its temper-ature has dropped apredetermined number ofdegrees below that of the steam.

On the other hand, the unitheater must be fitted with a trapthat will discharge condensateimmediately as it forms. Theslightest waterlogging in this casewould reduce heat output andcause the heater to blow cool air.Condensate held back in the unitheater will also promote corrosionand unnecessarily reduce the lifeof the heater tubes.

The extent to which waterlog-ging of a steam space can betolerated is clearly a significantfactor in steam trap selection.The wrong choice of trap is at theroot of many instances of poorplant performance.

TRAP TYPE USUAL DISCHARGE PATTERN

Thermodynamic Disc Blast action. Cyclical Open/Closed

Balanced Pressure Thermostatic Blast action. Cyclical Open/Closed on Light loadsContinuous Modulating on Heavier loads

Bimetallic Thermostatic Continuous dribble discharge

Liquid Expansion Thermostatic Continuous dribble discharge

Float and Thermostatic Continuous discharge-varies with loads

Inverted Bucket Blast action. Cyclical Open/Closed on Light loadsModulating on Heavier loads no definite closure

Steam Traps and the Removal of Condensate

42

Lifting Of CondensateThe rate at which a steam

trap can discharge condensatedepends on the size of the valveorifice and the “differential pres-sure”, the difference in pressurebetween the inlet and the outlet ofthe trap.

If a steam trap discharges toatmosphere, the differential pres-sure across the trap will be thesame as the upstream steampressure. The same will be true ifthe trap discharges into a returnline at a lower level which allowsthe condensate to gravitate backto the boiler feed tank.Unfortunately, such an arrange-ment is often ruled out becauseeither the boiler feed tank is high-er than the traps or the returnmain has to run at high level toclear obstructions. In thesecases, the condensate must belifted either directly by steampressure in the apparatus or by apump. In this section we are par-

ticularly concerned with the prob-lems which may arise from liftingcondensate by the steam pres-sure at the trap inlet.

For every 1 psi of steam pres-sure at the trap, condensate canbe lifted to a height of approxi-mately 2.3 feet. In order to liftcondensate, the trap must havepositive steam pressure at alltimes. There are disadvantagesto lifting condensate in this man-ner. In the first place, thenecessary steam pressure maynot always be available at the trapinlet. If, for example, the normaloperating pressure is 25 psi, it istheoretically possible to lift thecondensate 57.5 feet. However,on a cold start up, the steampressure may for a time drop to,or even below, zero. Until thispressure builds up, condensatecannot be removed from theequipment and will collect in thesteam space. This will result in agreatly extended heat up period.

The condensate will also preventany air from escaping through thesteam trap which makes theproblem even worse.

If the equipment is tempera-ture controlled, the very action ofthe control may reduce the steampressure below the point at whichit can successfully lift condensateto an overhead return line. Onceagain the steam space will water-log until the control valve opens,resulting in poor temperaturecontrol and the possibility ofwaterhammer as the steam rush-es into the waterlogged steamspace. Additionally, if the steamspace is a coil, considerable ero-sion and corrosion may takeplace.

It must be remembered thatcertain types of steam traps arelimited as to the amount of “backpressure” against which they willsatisfactorily operate.

Figure 35Requirements for Steam Trap/Applications

REQUIREMENTS FOR STEAM TRAP/APPLICATIONS

TYPES DISCHARGE DISCHARGE TEMPERATURE AIR HANDLING

Balanced Pressure Continuous (Dribble) 20 - 40 deg. F Subcool Excellent

Bi-metallic Continuous (Dribble) 50 - 100 deg. F Subcool Excellent (but may close too quickly due tosubcooling)

Inverted Bucket Intermittent Saturated Steam Temperature Limited

Float and Thermostatic Continuous Saturated Steam Temperature Excellent

Disk (TD) Intermittent 2 to 10 deg. F Subcool Limited

APPLICATION REQUIREMENTS

APPLICATION DISCHARGE SUB-COOL AIR HANDLING

Drip Continuous or Intermittent Little Little

Tracer/Critical Continuous or Intermittent Little Little

Tracer/Non-Critical Continuous Some None

Process Continuous None Much

Steam Traps and the Removal of Condensate

43

As the USA’s leading provider of steam system solutions, Spirax Sarco recognizes that no two steam trappingsystems are identical. Because of the wide array of steam trap applications with inherently different characteristics,choosing the correct steam trap for optimum performance is difficult. Waterhammer, superheat, corrosive conden-sate, or other damaging operating characteristics dramatically affect performance of a steam trap. With over 80 yearsof experience in steam technology, Spirax Sarco is committed to helping its customers design, operate and maintainan efficient steam system. You have our word on it!

1st Choice 2nd ChoiceFloat & Thermo- Balanced Liquid Inverted Float & Thermo- Balanced Liquid Inverted

Application Thermostatic Dynamic® Pressure Bimetallic Expansion Bucket Thermostatic Dynamic® Pressure Bimetallic Expansion Bucket

Steam Mains to 30 psig ✓ ✓

30-400 psig ✓ ✓

to 600 psig ✓ ✓

to 900 psig ✓ ✓

to 2000 psig ✓ ✓

with Superheat ✓ ✓

Separators ✓ ✓

Steam Tracers Critical ✓ ✓

Non-Critical ✓ ✓

Heating Equipment

Shell & Tube Heat Exchangers ✓ ✓*

Heating Coils ✓ ✓*

Unit Heaters ✓ ✓*

Plate & Frame Heat Exchangers ✓ ✓*

Radiators ✓

General Process Equipment

to 30 psig ✓ ✓*

to 200 psig ✓ ✓*

to 465 psig ✓ ✓*

to 600 psig ✓

to 900 psig ✓

to 2000 psig ✓

Hospital Equipment

Autoclaves ✓ ✓

Sterilizers ✓ ✓

Fuel Oil Heating

Bulk Storage Tanks ✓ ✓

Line Heaters ✓

Tanks & Vats

Bulk Storage Tanks ✓ ✓

Process Vats ✓ ✓

Vulcanizers ✓ ✓

Evaporators ✓ ✓

Reboilers ✓ ✓

Rotating Cylinders ✓ ✓

Freeze Protection ✓

Figure 36: Steam Trap Selection Guide

* With the addition of thermostatic air vent device

Steam Traps and the Removal of Condensate

44

Steam Trap SizingThe benefits of selecting the

best type of steam trap for agiven application (Fig. 35 & 36)will be wasted if the trap is notcorrectly sized. It is bad practiceto choose a 3/4" trap simplybecause it has to go on a 3/4"drain line. In order to size asteam trap, we obviously need toknow the quantity of condensateto be handled in a given time.The makers of most standardkinds of steam equipment usuallysupply reliable figures on the con-densation rates of theirequipment. If such information isnot available, it has to beacquired either by calculation orpractical measurement of thecondensate produced. A test pro-cedure which will give reasonablyaccurate results is set out at theend of this section.

Reference has already beenmade to “start-up” loads and “run-ning” loads in this course. Weknow that steam will condensemost rapidly on start up when thesystem is cold. It is for this rea-son that it is common practice tosize traps using a safety factor.The trap selected should be ableto handle twice the normal run-ning load, or as much as 3 timesthe running load following anautomatic temperature control.An undersized trap will causewaterlogging of the steam spacewhen it can be least afforded.

Steam Pressure and TrapCapacity

We know that for a steamtrap to operate, there must be ahigher pressure at its inlet thanthere is at its outlet. The actualamount of condensate which thetrap can discharge is governed bythe following three factors:1. The differential pressure2. The size of the trap discharge

orifice.

3. The temperature of the con-densate.

We must now examine thesefactors in more detail.

1. Differential Pressure

The maximum amount ofcondensate the trap will dis-charge will increase as thedifferential pressure (the differ-ence in pressure between theinlet and outlet of the trap)increases. In other words, thecapacity of a trap discharging toatmosphere with steam at 75 psiwill be greater than that of thesame trap with steam at 30 psi.The capacity does not, however,increase in proportion to the pres-sure.

It is not wise to assume thatthe pressure at which steam issupplied to a piece of equipmentwill be the pressure on the inlet toits steam trap. Pressure lossesoften mean that the steam pres-sure at the trap will beconsiderably less than the steamsupply pressure.

If a steam trap is dischargingcondensate to atmosphere, theoutlet pressure will be atmos-pheric and, therefore, thedifferential pressure will be thesame as the gauge pressure atthe trap inlet. However, if the trapdischarges into a main which isunder pressure, the differentialpressure will be reduced by anamount which can be determinedby subtracting the outlet pressurefrom the trap inlet pressure. Thequantity of condensate which thetrap is capable of passing in agiven time will be reducedaccordingly.

2. Size of Discharge Orifice

The size of the discharge ori-fice not only helps to determinethe capacity of the trap but alsooften fixes the maximum pres-sure at which the trap willoperate. Reference to the steam

trap section reveals that the vastmajority of the traps describedhave the valve on the pressureside (the inlet side) of the valveseat. The only notable exceptionto this arrangement occurs in thebimetallic type of traps where thevalve is on the outlet side of thevalve seat. In the case of trapswith the valve on the pressureside of the valve seat, the valve,when closed, will be held on itsseat by the steam pressure.According to the type of trap inquestion, the thermostatic ele-ment, ball float or bucket musthave enough force to pull thevalve away from its seat againstthis pressure.

In any given trap, the force isa fixed amount. Force Required= pressure x area.

The maximum pressure atwhich the valve of the trap canopen is the pressure at which thisoperating force is just greaterthan the valve seat area multi-plied by the pressure in the trapbody.

In the case of traps with thevalve at the outlet side of thevalve seat, the situation is differ-ent. In this type, the steampressure tends to open the valve,so the maximum pressure atwhich the trap can close is whenthe operating force is just greaterthan the steam pressure multi-plied by the valve seat area.

3. The Temperature Of TheCondensate.

The capacity of a trap shouldnever be based on the amount ofcold water the trap will pass atany given differential pressure.Condensate in a steam trap isusually at a temperature aboveatmospheric boiling point. Whenthe condensate is passingthrough the valve seat of the trap,its pressure is quickly reducedand a certain amount of flash

Steam Tracing

45

steam is generated. This flashsteam tends to choke the dis-charge orifice, reducing itseffective area. As the conden-sate temperature rises, theamount of flash steam generatedwill increase and the dischargecapacity of the trap will decrease.The extent of which condensatetemperature affects the trap’s dis-charge capacity is relative to itstemperature below saturationtemperature -- lower tempera-tures, lower flashing rates.

Steam TracingThere are two typical applica-

tions of tracing. They aretypically referred to as eitherprocess fluid (critical) or freezeprotection (non-critical) tracing.There are different requirementsfor each as far as heat is con-cerned, so we will separate theirrequirements prior to discussinghow to attach tracing to the appli-cation.

Tracing is as its nameimplies, a pipe or tube followingeither process fluid lines or lineswhere it is desirable to preventfreezing during the wintermonths. Steam tracing is the dis-tribution of steam through smallbore tubing or pipes which basi-cally transfer heat to a larger pipeto keep fluids from becoming vis-cous, solidifying or freezing.

Process (Critical) TracingTypically, process fluids are

already at as high a temperatureas desired. They have passedthrough heat exchange equip-ment and absorbed as much heatas necessary to keep the viscosi-ty to a level that they flowsmoothly through the piping.Tracing is installed running alongthe fluid lines mainly to keep the

product at the specific tempera-ture it already has. It is, therefore,a heat maintainer, and not a heatexchanger. Because of this, theconsumption of the steam is usu-ally very low. In fact, it is one ofthe smallest steam consumers ina given plant. The fact is howev-er, that in some plants (such asHydrocarbon Processing facili-ties), they account for as much as70% of the steam using locations.The fact that they consume verylittle steam is then overshadowedby the sheer numbers of lines.

Freeze Protection (Non-Criti-cal)

In areas of the country wherefreezing conditions prevail duringwinter months, many differenttypes of systems require protec-tion from freeze-up. Obviously,these lines are water lines or per-haps metering equipment thatuse water in sensor tubes todetect flow of gases, etc. Tracinglines keep the water from freezingwhich will in turn possibly rupturepiping, tubing or equipment.Sometimes, liquids that will notnecessarily freeze become very

thick if not heated and kept heat-ed throughout their processing.An example usually used is “thickas molasses”.

There are many differentways of attaching tracing andthere are many different types ormethods of using the tracing con-cept. The following discussesthese.

Typically, tracing is coppertubing attached to a pipe filledwith some type of liquid (Fig. 37).

The method of attaching alsovaries from plant to plant andspec to spec. The lines them-selves can be banded orstrapped, (when temperature dif-ferences between the steam andproduct fluid are low and steelpipe is used), attached usingHeat Conducting Paste (Fig. 38)and Channels and straight wiringthem in place. The placement ofthe tracer tubing is more impor-tant in most cases than themethod used for attachment. Inwhichever method of attaching isselected, it is most important toavoid crimping the tubing.

Figure 37Tracer Line Attachments

18" Max.

Process Fluid

Tracer Tubing

Process Fluid

Tracer Tubing

Stainless Wire (Wrapped)

Insulation

Process Fluid

Steam Tracer

Steam Tracing

46

Figure 38Tracer Using Heat Transfer Paste

Figure 39Welded Steam Tracer Pipe

Another popular method oftracing is the use of jacketed pipe(Fig. 40).This method of tracing isused particularly when there isneed to keep a fluid (such asSulfur) from solidifying in thepipes. We will look at each of themethods mentioned above anddiscuss some do’s and don’ts.

Attaching TracersThe easiest method of trac-

ing is by attaching copper tubingto the pipe. It is used mostlybecause of the abundance ofcopper tubing and the cost whichis relatively low. The tubing isattached in the lower quadrant ofthe pipe being traced (Fig. 41).Another important considerationin tracing is to oppose the twoflows, fluids in the process pipingand steam in the tracer tubes.This may not always be prac-ticed, however, but there aresome solid reasons why onewould want to consider this.Think about what the tracer job is- maintain heat already absorbedby the process fluid. As it trans-fers from point “A” to point “B” inthe plant, heat will naturally belost through the insulation. The

job of the tracer then is to allowtransfer of the heat of the steaminto the flowing fluids as it is lostto the atmosphere.

The tracer line then shouldalso be installed running in astraight line as far toward the bot-tom of the piping as is possible(Fig. 42). The tracer is housedinside the insulation wrapping onthe pipe, and we gain much ben-efit from attaching it in thismanner. Heat, which you mayrecall, rises naturally and sur-rounds the piping allowing for asmuch natural conduction of BTU’sas possible. This heat barrieralso reduces the heat losses fromthe process fluids.

On some occasions, theamount of heat available andtemperature of the steam is suchthat spacers are used to preventburning the liquids on the insideof the process lines. This couldcause coking (burning) of thelines and also restrict flow of theprocess. When spacers areused, it is important that the insu-lation be sized to allow for theextra space required. It may alsobe advisable to label the outside

of the insulation with informationsuch as “traced” and maybe eventhe number of tracer linesattached along with the pressuresbeing used. This may help infuture maintenance of the systemitself. It may also help in usingthe numbers of tracers as theyare needed.

There may be times when thenumber of tracer lines being usedcan be reduced. For example, aprocess pipe during the wintermonths may require multiple trac-er lines to insure that the fluidsremain at the proper temperature.However, during the summermonths, the numbers of tracerlines may be reduced because ofless heat loss through the insula-tion. Some plants list the steammanifold header number wherethe on/off valves may be found tohelp with reducing the amount ofsteam being consumed unneces-sarily.

Insulation

Process Fluid

Heat Transfer Paste

Tracer Tube

Insulation

Process Fluid

Heat Transfer PasteTracer Tube

Steam Tracing

47

Figure 40Single Section of Jacketed Pipe

Figure 41Pipe Support

Figure 42Horizontal Tracing

Jacketed PipeJacketed pipe (Fig. 43 on the

following page) may be an alter-native method of tracing usedwhen the process fluids require ahigh temperature to stay flowingwith the least amount of resis-tance. These liquid lines areusually fluids that set up at veryhigh temperatures such as sulfur.They are very specialized tracerlines as the steam jacket com-pletely encircles the process fluidline. This pipe within a piperequires special attention and willrequire specialized traps toensure the proper drainage.Jacketed pipe obviously transfersa lot of heat in comparison tosteam tracer lines made of cop-per or stainless steel. This typeof tracer line usually is used whenthe temperature of the processfluid is about the same tempera-ture as the steam being used.The lines are usually flange fittedand the passing of steam fromone line to the next requiressteam flow to ensure the passageof steam on down the lines. Thechart (Fig. 44 on the followingpage) will help in sizing the steamconnection line size for the size ofjacketed pipe being used. Eachjacketed line has a connection atthe bottom on the downstreamline that is used to drain eachsection individually. This is impor-tant because this particular typeof specialized tracer is truly act-ing like a heat exchanger. Thesteam consumption of this type oftracing may be much higher thanthe smaller tubing type tracersused in plants.

Steam In Steam Out

Condensate Out

ProcessFlow In

Multiple tracer lines attached to lower halfof process fluid lines. Insulation not shown

Process Pipe

Tracers

PipeSupport

Tracing lines that must pass over flanges should pass in thehorizontal. If it is required to place a connection fitting along

side of flanges, they should also be placed horizontally.

Steam Tracing

48

Figure 43Jacketed Tracing System

Steam ManifoldsSteam manifolds are most

helpful in running the steam tothe system. Manifolds are easilymaintained and located asopposed to individually valvingareas of a plant. A centralizedlocation for manifolds (Fig. 45a)ensure operators of turning onand off the correct valves for trac-ing. Manifolds should be fittedwith a tag that identifies whatlines are traced and how manylines are going to that particularprocess line. Other considera-

tions for manifolding steam linesis the ability to control automaticvalves on and off. If the tracingon a particular manifold is usedfor freeze protection, ambientsensors on control valves willautomatically turn the steam onwhen needed. This ensures thatthe steam is turned on and offproperly. The important wordhere is “off”. It is not unusual tosee steam lines turned on duringa particular time of year. Theconditions may change at anygiven time and the steam may not

be required. If the steam isalways on, then it is always usedeven in small quantities. This iswasteful and should be avoided.As this course has mentioned, itis important to conserve this pre-cious and costly commoditycalled steam. Even though trac-ing systems individually use smallamounts of steam, remember thesheer numbers of lines that maybe involved.

Condensate ManifoldsCondensate manifolds (Fig.

45b) are also very useful in anytypical plant that uses tracing.The condensate manifold itselflocates traps and tracers in asmall given area. The conden-sate from the tracer lines isusually very high quality conden-sate and should be collected andreturned to the boiler. There isnormally no cross contaminationof product fluids to tracer lines.Condensate manifolds also makeit very easy to find and monitorthe tracing traps being used.Each trap station on a manifold

Stop Valve

25P Valve

Steam Air Vent

TD 42

Process Pipe

Jacket

NOTE: Each section of jacketed pipeshould be trapped. Steam jumper linesshould continue over the top of the flanges.

Condensate to grade

Figure 44Steam Connection Line Sizing for Jacketed Pipe

STEAM CONNECTION LINE SIZING FOR JACKETED PIPE

Product Line Jacket Diameter Steam Connection2-1/2" 4" 1/2"

3" 6" 3/4"

4" 6" 3/4"

6" 8" 3/4"

8" 10" 1"

10" 12" 1"

Steam Tracing

49

Figure 45aSteam Manifolds

Figure 45bCondensate Manifolds

should be tagged with a numberthat identifies the trap, size,pressure, etc. so that a mainte-nance program can helpdetermine the correctness ofeither the traps being selectedor size of trap being used.These manifolds can be eitherhorizontally or verticallydesigned depending on thespace available and the specifi-cation of any given plant.

The following charts (Fig.46) and illustrations (Fig. 47)may be helpful in sizing, select-ing and specifying tracers andtheir types.

Figure 46

Steam Out

Steam

Out

Air Vent

Steam Trap

Steam Trap

Horizontal Manifold

Vertical M

anifold

NUMBER OF 1/2”TRACERS USED WITH DIFFERENT SIZES OF PRODUCT LINES

Type A Type B Type C

General Frost Where solidification Where solidificationprotection or may occur at temps may occur at temps

where solidification between between may occur at 75-150°F 150-300°F

temps below 75°F

Product Line Size Number of 1/2" Tracers Number of 1/2" Tracers Number of 1/2" Tracers1" 1 1 1

1-1/2" 1 1 22" 1 1 23" 1 1 34" 1 2 36" 2 2 38" 2 2 3

10-12" 2 3 614-16" 2 3 818-20" 2 3 10

RECOMMENDED HEADER SIZE FOR CONDENSATE LINES

Header Size Number of 1/2" Tracers1" Up to 5

1-1/2" 6 to 102" 11 to 25

Condensate Management

50

Figure 47Switch Back Tracing Line

Condensate ManagementWhen steam condenses,

energy is transferred to the coolermaterial to be heated. Thisaccounts for only around 75% ofthe energy supplied in the boilerto produce the steam. Theremainder, about 25%, is still heldby the condensed water.

As well as having heat con-tent, the condensate is distilledwater: ideal for use as boiler feedwater. An efficient installation willcollect every drop of condensateit economically can, and eitherreturn it to the deaerator or boilerfeed tank, or use it in the process.

Condensate is dischargedthrough steam traps from a high-er to a lower pressure. As a resultof this drop in pressure, some ofthe condensate will then re-evap-orate, and is referred to as flashsteam. The proportion that willflash off differs according to thelevel of pressure reductionbetween the ‘steam’ and ‘conden-sate’ sides of the system, but a

figure of 10-15% by mass is typi-cal (Fig. 48).

About half of the energy men-tioned above (i.e. 12.5% of thetotal energy supplied) could belost through flash steam (Fig. 49).

Flash Steam Recovery is,therefore, an essential part ofachieving an energy efficient sys-tem.

This section will bring togeth-er Condensate Recovery,Condensate Removal and FlashSteam Recovery under the head-ing of Condensate Management.The objective is to examine thetechnical aspects for the benefitof the expert and then to use thisas a basis to provide simpleguide lines for the occasionaluser.

Condensate line sizing playsan important role in successfullycontrolling and collecting conden-sate. Sizing condensate linesrequires much planning to controlvelocities of liquids and gases. It

Figure 48Approximate amount of flashsteam in Condensate

Figure 49Approximate amount of energy inCondensate

FlashSteam 15%

Water85%

Water50%

FlashSteam 50%

Steam Trap

Note:Condensate

pipe isalways

sloped in adownwarddirection.

In somecases, usingswitch backtracing addsmore surfacecontact area.

End View

Tracing Valves

Separate Steam Traps foreach section of tracer

Steam In

Steam In

should be remembered that con-densate lines are, in fact,bi-phase systems that requireproper planning. Review theCondensate Line Sizing Chart forassistance in this area (Fig. 50).

You will note that it is recom-mended to increase the line sizeon the discharge of all steamtraps. This is intended to allowfor the flashing that will beexpected when steam traps dis-

Condensate Management

51

6000

3000

4000

2000

1000

600

100

66

50

33

50,000

30,000

20,000

10,000

8000

20

30

40

5060

80

100

200

300

500

8001000

2000

3000

5000

Fla

sh S

team

Flo

wra

te (

lb/h

)

Velocity(ft/sec)

Velocity(ft/min)

Pressure in

condensate line or

flash tank (psig)

Pipe Size (schedule 40)

A

D

E

C

RecommendedService

Condensate ReturnLine Sizing

Vent Pipe Sizing

Flash TankDiameter Sizing

10

17

28"30"24"

26"20"

18"16"

14"12" 10" 8" 6" 5" 4" 3"

2-1/2"2"

1-1/2"1-1/4"

1" 3/4"1/2"

B

1008060403020

105

0

1008060403020

1050

1008060403020

1050

Multiply chart velocityby factor belowto get velocity

in schedule 80 pipe

Pipe Size1/2"3/4" & 1"1-1/4" & 1-1/2"2" & 3"4" to 24"26" to 30"

Factor1.301.231.151.121.11.0

10

Figure 50: Condensate Line Sizing Chart

charge condensate into lowerpressure systems. A chart is pro-vided to assist in quicklyestimating the amount of flashthat can be produced. The volu-metric change of condensateflashing into steam may causesubstantial increasing velocitiesthat may damage existing con-

densate recovery systems.

Flash Steam RecoveryWhen hot condensate under

pressure is released to a lowerpressure, its temperature mustvery quickly drop to the boilingpoint for the lower pressure asshown in the steam tables. The

surplus heat is utilized by thecondensate as latent heat caus-ing some of it to re-evaporate intosteam.

The quantity of “flash steam”available from each pound of con-densate can be calculated usingthis formula:

Condensate Management

52

Percentage Quantity of FlashSteam

= Sensible Heat at the Higher Pressure

- Sensible Heat at the Lower Pressure

÷ Latent Heat of the Lower Pressure

Figure 51: Percent FlashSteam

Pressure Atmosphere Flash Tank Pressure (psig)(psig) 0 2 5 10 15 20 30 40 60 80 100

5 1.7 1.0 010 2.9 2.2 1.4 015 4.0 3.2 2.4 1.1 020 4.9 4.2 3.4 2.1 1.1 030 6.5 5.8 5.0 3.8 2.6 1.7 040 7.8 7.1 6.4 5.1 4.0 3.1 1.3 060 10.0 9.3 8.6 7.3 6.3 5.4 3.6 2.2 080 11.7 11.1 10.3 9.0 8.1 7.1 5.5 4.0 1.9 0

100 13.3 12.6 11.8 10.6 9.7 8.8 7.0 5.7 3.5 1.7 0125 14.8 14.2 13.4 12.2 11.3 10.3 8.6 7.4 5.2 3.4 1.8160 16.8 16.2 15.4 14.1 13.2 12.4 10.6 9.5 7.4 5.6 4.0200 18.6 18.0 17.3 16.1 15.2 14.3 12.8 11.5 9.3 7.5 5.9250 20.6 20.0 19.3 18.1 17.2 16.3 14.7 13.6 11.2 9.8 8.2300 22.7 21.8 21.1 19.9 19.0 18.2 16.7 15.4 13.4 11.8 10.1350 24.0 23.3 22.6 21.6 20.5 19.8 18.3 17.2 15.1 13.5 11.9400 25.3 24.7 24.0 22.9 22.0 21.1 19.7 18.5 16.5 15.0 13.4

Percent flash for various initial steam pressures and flash tank pressures.

To simplify this procedure wecan use the chart (Fig. 51) to readoff the percentage of flash steamproduced by this pressure drop.An example would be if we had100 PSIG saturated steam/con-densate being discharged from asteam trap to an atmospheric,gravity flow condensate returnsystem (0 PSIG), the flash per-centage of the condensate wouldbe 13.3% of the volume dis-charged.

Conversely, if we had 15PSIG saturated steam discharg-ing to the same (0 PSIG)atmospheric gravity flow returnsystem, the percentage of flashsteam would be only 4% by vol-ume. These examples clearlyshow that the amount of flashreleased depends upon the differ-

ence between the pressuresupstream and downstream of thetrap and the corresponding tem-peratures of those pressures insaturated steam. The higher theinitial pressure and the lower theflash recovery pressure, thegreater the quantity of flashsteam produced.

It must be noted here that thechart is based upon saturatedsteam pressure/temperature con-ditions at the trap inlet, and thatthe condensate is discharged asrapidly as it appears at the trap.Steam traps that subcool the con-densate, such as balancedpressure thermostatic andbimetallic traps, hold condensateback in the system allowing it togive up sensible heat energy andcausing it to cool below the satu-rated steam temperature for thatpressure. Under those circum-stances, we must calculate fromthe formula above the percentageof flash steam produced, but theamount of subcooling (the con-densate temperature) must beknown before calculating.

Before discussing the ways ofrecovering flash steam and whywe want to recover it, there aretwo important practical pointswhich should be noted:

First, one pound of steamhas a specific volume of 26.8cubic feet at atmospheric pres-sure. It also contains 970 BTU’sof latent heat energy. This meansthat if a trap discharges 100pounds per hour of condensatefrom 100 PSIG to atmosphere,the weight of flash steamreleased will be 13.3 pounds perhour, having a specific volume of356.4 cubic feet. It will also have12,901 BTU’s of latent heat ener-gy. This will appear to be a verylarge quantity of steam and maywell lead to the erroneous conclu-sion that the trap is passing livesteam (failed open).

Another factor to be consid-ered is that we have just released13.3 pounds of water to theatmosphere that should havegone back to the boiler house forrecycling as boiler feed water.Since we just wasted it, we nowhave to supply 13.3 pounds offresh city water that has beensoftened, chemically treated andpreheated to the feedwater sys-tem’s temperature before puttingthis new water back into the boil-er.

Secondly, the actual forma-tion of flash steam takes placewithin and downstream of thesteam trap orifice where pressuredrop occurs. From this pointonward, the condensate returnsystem must be capable of carry-ing this flash steam, as well ascondensate. Unfortunately, dur-ing the past 80 years, condensatereturn lines have been sizedusing water volume only and didnot include the flash steam vol-ume that is present.

Condensate Management

53

The size of the vessel has tobe designed to allow for areduced velocity so that the sep-aration of the flash steam andcondensate can be accomplishedadequately, so as not to havecarry-over of condensate out intothe flash steam recovery system.This target velocity is ten feet persecond per ASHRAE standardsto ensure proper separation. Thecondensate drops to the bottomof the flash tank where it isremoved by a float and thermo-static steam trap.

A number of basic require-ments and considerations have tobe met before flash steam recov-ery is a viable and economicalproposition:

1. It is first essential to have asufficient supply of conden-sate, from loads at sufficientlyhigher pressures, to ensurethat enough flash steam willbe released to make recov-ery economically effective.The steam traps, and theequipment from which theyare draining condensate,

must be able to function sat-isfactorily while accepting thenew back pressure applied tothem by the flash recoverysystem.

In particular, care is neededwhen attempting flash steamrecovery from condensate, whichis leaving temperature controlledequipment. At less than fullloads, the steam space pressurewill be lowered by the action ofthe temperature control valve. Ifthe steam space pressureapproaches or even falls belowthe flash steam vessel pressure,condensate drainage from thisequipment becomes impracticalby a steam trap alone, and theequipment becomes “stalled” andwater logging will most definitelyoccur. We will look at this prob-lem in much further detail in ournext section “CondensateRecovery”.

2. The second requirement is asuitable use for low pressureflash steam. Ideally, lowpressure load(s) requires atall times a supply of steam

Figure 52Operation of a flashsteam vessel

PressureGaugeConnection

Condensate Outlet

Flash Steam Outlet

Condensate andFlash Steam Inlet

The specific volume of waterat 0 PSIG is .016 cubic feet perpound, compared to 26.8 cubicfeet per pound for flash steam atthe same pressure. Sizing ofcondensate return lines from trapdischarges based totally on wateris a gross error and causes linesto be drastically undersized forthe flash steam. This causescondensate lines to becomepressurized, not atmospheric,which in turn causes a backpres-sure to be applied to the trap’sdischarge which can causeequipment failure and flooding.

This undersizing explainswhy the majority of 0 PSI atmos-pheric condensate returnsystems in the United States donot operate at 0 PSIG. To takethis thought one step further forthose people who perform tem-perature tests on steam traps todetermine if the trap has failed,the instant we cause a positivepressure to develop in the con-densate return system by flashsteam, the condensate return linenow must follow thepressure/temperature relation-ship of saturated steam. So, traptesting by temperature identifiesonly that we have a return systemat a certain temperature above212°F (0 PSIG) and we can thendetermine by that temperaturethe system pressure at which it isoperating. Elevated condensatereturn temperatures do not nec-essarily mean a trap has failed.

If the flash steam is to be recov-ered and utilized, it obviously hasto be separated from the conden-sate. This is best achieved bypassing the mixture of flashsteam and condensate throughwhat is known as a “flash tank” or“flash vessel” (Fig. 52). A typicalarrangement is shown.

Condensate Management

54

which either equals orexceeds the available flashsteam supply. The deficit canthen be made up through apressure reducing valve set.If the supply of flash steamexceeds the demand for it,the surplus may have to bevented to waste through abackpressure relief valve.

Thus it is possible to utilizethe flash steam from processcondensate on a space heatinginstallation, but the savings willonly be achieved during the heat-ing season. When heating is notrequired, the recovery systembecomes ineffective.

Wherever possible, the betterarrangement is to use flashsteam from process condensateto supply process loads, and thatfrom heating condensate to sup-ply heating loads. Supply anddemand are then more likely toremain “in step”.

When all else fails, in manyfacilities there is always a needfor hot water, especially in theboiler house. This can be sup-plied via a heat exchanger andthe use of flash steam.

3. It is also preferable to selectan application for the flashsteam which is reasonablyclose in proximity to the highpressure condensate source.Piping for low pressure steamis inevitably of larger diame-ter. This makes it somewhatcostly to install. Furthermore,the heat loss from largediameter pipes reduces thebenefits obtained from flashsteam recovery and in theworst cases could outweighthem.

Flash steam recovery is sim-plest when being recovered froma single piece of equipment thatcondenses a large amount ofsteam, such as a large steam to

water converter or a large airhandling coil bank, but we can-not forget that flash steamrecovery systems by design willapply a backpressure to theequipment that is being drainedor to the flash steam source.Another very common area fromwhich flash steam is recovered isboiler blowdown. Dissolved solidsthat create the need for boilerblowdown drop out and will pro-duce usable flash steam andcondensate.

Boiler blowdown flash steamrecovery (Fig. 53) is a very effi-cient method for recovery. It notonly is a continuous supply ofvaluable heat energy to be uti-lized, but it is in close proximity toan area of definite need as in theboiler feed or deaerator systemthat demands a constant sourceof low pressure heat energy forpreheating the boiler make upwater supply. This simple instal-lation is shown below.

Figure 53Boiler Blowdown HeatRecovery System

Pilot Operated BackPressure Valve

Safety Valve

BoilerBlowdown

Source

Steam Trap Set

Steam Trap SetFlash Vessel

Cold Water

Hot Water

Condensate Management

55

Another area that works verywell in the utilization of flashsteam recovery is large multi-section air heating coils (Fig. 54).Many times flash steam can besupplied to a coil added to thesystem to maximize use of theflash steam supplied by the pri-mary coils in the system. Anexample is shown in the followingsketch. This example clearly ful-fills the basic requirements ofhaving a flash steam recoverysystem which is in step withdemand.

Only when air coils are calledupon to supply heat does theflash steam recovery systembecome available, and it can thenbe condensed in the first air coilwhich is essentially a pre-heater.This simple arrangement ensuresthat higher pressure traps are notsubjected to any backpressure on

Figure 54Control of FlashSteam Pressure

start up of the system.

Another method of flashsteam recovery is through a ventcondenser on a receiver (Fig. 55on following page). Flash steamis allowed to flow up through thecondenser (heat exchanger), thathas a supply of fluid flowingthrough it, to capture the heatenergy contained in the flashsteam. This type of system is an“atmospheric” pressure system,which allows condensate fromthe flash steam to flow by gravityback into the original condensatereceiver. This provides the userwith recovery of heat energy andthe complete recovery of all con-densate from that system, andenables the user to accomplishthis without presenting all of theequipment in that system withany backpressure.

Condensate Recovery Sys-tems

The importance of effectivecondensate removal from steamspaces has been stressedthroughout this course. If maxi-mum steam system efficiency isto be achieved, the best type ofsteam trap must be fitted in themost suitable position for theapplication in question. Havingconsidered how to best utilize anyflash steam which may be avail-able, we must now decide what todo with the condensate whichremains.

There are a number of rea-sons why condensate should notbe allowed to discharge to drain.The most important considerationis the valuable heat which it con-tains even after flash steam hasbeen recovered. It is possible touse condensate as hot process

Control Valve

PressureReducingValve

Steam

AirFlow

Condensate

Flash Steam

Steam TrapFlashVessel

Condensate Management

56

water but the best arrangement isto return it to the boiler house,where it can be re-used as boilerfeed water without further treat-ment, saving preheating fuel, rawwater and the chemicals neededfor boiler feed treatment. Thesesavings will be even greater incases where effluent chargeshave to be paid for the dischargeof valuable hot condensate downthe drain.

Condensate recovery sav-ings can add up to 25 to 30% ofthe plant’s steam generating

costs. One justifiable reason fornot returning condensate is therisk of contamination. Perforatedcoils in process vessels and heatexchangers do exist and thecross contamination of conden-sate and process fluids is alwaysa danger. If there is any possibil-ity that the condensate iscontaminated, it must not bereturned to the boiler. Theseproblems have been lessened bythe application of sensing sys-tems monitoring the quality ofcondensate in different holding

areas of a plant to determine con-densate quality and providing ameans to re-route the conden-sate if contaminated.

Vented “open” return sys-tems have been utilized for 80plus years where the conden-sate is allowed to flow bygravity to a central collectionreceiver and then the use ofelectrically driven pumpsreturn it to the boiler housewhen these receivers are full.

Figure 55Flash Steam Condensor or Heater

Cold Water Supply

Steam or Gas Inlet

Heat Exchanger

CondensateReturn System

Condensate Management

57

Electrically Driven PumpsElectrical driven pumps (Fig.

56) have been used to collect andreturn this condensate. When uti-lized on radiation heatingapplications, condensate usuallyreturns at relatively low tempera-tures, 160-180°F, which does notprovide any great difficulty for theelectric pumps. When conden-sate temperatures approach200°F or above, the electricallydriven pumps begin to experi-ence a phenomenon known as“cavitation”. Cavitation is theflashing of higher temperaturecondensate as it enters the eye ofthe impeller, where the pressuredrops to below atmospheric pres-sure. The pump becomes vapor(steam) bound. These pumpsmust have a flooded impellerchamber in order to maintain aconstant flow of water to cleanseand cool the “mechanical seals”of the pump.

If the mechanical seals areallowed to run dry for any amountof time, the maximum operatingtemperature of the seal isreached in a very short time. Thiscauses permanent mechanicalseal damage, which in turn caus-es leakage of condensate to thefloor or even worse, up into theelectrical motor.

Many years ago, electricpump manufacturers suppliedtheir pumps with restrictions inthe pump discharges in order toprovide the customer with theprecise discharge pressure andflow conditions that he requested.Those same manufacturers havesince stopped installing throttlingorifices in these pumps and haveonly informed the users via theinstallation and maintenancemanuals, which never get deliv-ered to the job site. The installingcontractor installs, in the dis-charge of the pump unit, anisolation valve and a check valve.

Isolation valves have only twopositions in this industry, eitherfully open or fully closed. This isnot the required throttling valvethat the manufacturer recom-mended in his installationmanual. Since these isolationvalves are usually fully open dur-ing service, the pump will searchup and down its performancecurve until it finds the operatingpoint, which just overcomes thetrue system backpressure.When this is allowed to happen,the pump will not have the sameoperating characteristics as wasdesigned. This will change theNPSH required of the pump,which determines the maximumpumpable temperature of thecondensate that can be handledwithout cavitation. Hence, thecontinuous replacement ofmechanical seals of thesepumps. These pumps need to bethrottled to the designed operat-ing conditions, which means athrottling valve must be installeddownstream of the pump with apressure gauge between thepump discharge and the throttlingvalve, and the valve should beclosed until the designed operat-ing pressure is achieved on the

pressure gauge.

If cavitation problems stillexist due to elevated tempera-tures, the only recourse is to coolthe condensate down to apumpable temperature. Thissounds like a simple cure, but ifwe look at the oxygen solubilitychart (Fig. 57 on the followingpage), we see that as condensatecools down, the ability of thatwater to contain oxygen goes up.The more oxygen contained incondensate when it reaches theboiler house, the more chemicalsthat have to be added to removethat oxygen.

Sodium Sulfite is the chemi-cal added to condensate toremove this dissolved, containedoxygen and it takes 8 PPM ofSodium Sulfite to remove 1 PPMof oxygen. So cooling down thecondensate is certainly ananswer to pumping problems, butit causes the usage of morechemicals, increased heat energyto preheat this condensate backup and certainly will causedecreased life of the condensatereturn piping system due to theincreased corrosion attack.

Figure 56Electric Pump Operation

Condensate Management

58

Figure 57Solubility of Oxygen in Condensate

Non Electric Pressure Pow-ered Pumps

Non Electric PressurePowered Pumps have becomethe state of art method of con-densate pumping in industrytoday. This type of pump does notrequire any electrical connec-tions, has no high speed rotatingimpellers, no temperature sensi-tive mechanical seals or largeoversized receivers for storage ofcondensate (Fig. 58). The non-electric pressure powered pumpcan operate on steam, com-pressed air or any inert gas withpressures up to 300 PSIG.

In “open” atmospheric sys-tems (Fig. 59), there are severalbenefits to using this pumpingsystem. Receivers are not aslarge, condensate does not haveto cool down before pumping, thepump can be installed directlybelow heat exchange equipmentand will handle the condensate at212°F without any cavitation ormechanical problems. There isstill a need for a small receiver toallow steam traps that are dis-charging into it to sense acommon pressure of 0 PSIG soas not to apply any backpressureto any of the steam traps. Thecondensate is then pumped backto the boiler house for re-use.

Industry requirements formore efficient usage of steamenergy is demanding that con-densate not only be returned atthe highest possible tempera-tures, but that there are less andless atmospheric vents allowingflash steam to be lost. To accom-modate this need for efficientusage and the need for increas-ing equipment life expectancy ofall heat exchange equipment, the“closed” system (Fig. 60) ofremoval and recovery of conden-sate is becoming the designcriteria. In “closed” systems

Figure 58PPF/PPC Features

30 50 70 90 110 130 150 170 190 210

Condensate Temperature Deg. F

10

8

6

4

2

0

Oxy

gen

Con

tent

PP

M

ValveChangeoverMechanism

Check ValveCheck Valve

Inlet Port Outlet Port

Float andMechanism

Ductile Iron orFabricatedASME SteelBody

Condensate Management

59

condensate is removed, recov-ered at saturation temperaturesand returned directly back to thedeaerator in the boiler house.

The return of saturated tem-perature condensate in thismanner allows the boiler house toreduce the steam demand to thedeaerator to re-heat the conden-sate, reduces the need for morechemicals to be added to the con-densate, and ensures that theheat exchange equipment is keptdry at all times which eliminatescorrosion attack and potential coilfreezing. In the majority of appli-cations, these “closed” systemsare dedicated systems to a singlepiece of equipment.

Figure 59“OPEN” AtmosphericSystem

Figure 60“Closed” System

Pump Exhaust

Vent to Atmosphere

Receiver

PressurePoweredPump

Inlet Strainer

Filling Head

Condensate to Pump Operating Steamor Gas Supply

Steam TrapWhen Steam

Supply isUsed Height (H)

HeatExchanger

Air Vent

TemperatureControl

Steam Supply

CondensateReturn Line

PressurePoweredPump

FloatType

SteamTrap

Condensate Management

60

All temperature controlledequipment, as discussed earlier,has fluctuating steam pressuresinside the equipment based uponequipment load demands.Historically, we have dependedupon steam pressure to “lift” con-densate out of a piece ofequipment via the steam trap intothe condensate return system.Because of the operation of thetemperature control valves, therewould be times that there wouldbe sufficient steam pressure atthe trap inlet to overcome thecondensate return line pressureor the required lift.

At other times during opera-tion, there would not be enoughsteam pressure supplied to theequipment to lift condensate. Atthose times we would begin toflood the heat exchange equip-ment, causing either producttemperature fluctuations or evenworse, freezing of the air coils,because we were unable to effec-tively remove the condensate.Installing a pumping devicebetween the equipment and thetrap (Fig. 61) allows for conden-sate to be recovered andremoved from the steam equip-ment at all times duringoperation, whenever the steampressure is sensed in the equip-ment.

When the steam pressure isgreater than the condensatereturn pressure or lift, steampressure alone lifts the conden-sate out through the steam trap.However, when steam pressurein the equipment is equal to orlower than that of the condensatereturn system or lift, condensatecompletely fills the pump body,steam pressure is supplied to thepump and the condensate ispumped out through the steamtrap into the condensate returnsystem.

When the pump is pumpingcondensate, the condensatebeing produced in the equipmentis allowed to fall by gravity into thereservoir pipe, again ensuringthat the equipment is kept dry.Upon completion of the pumpingcycle, the pressure inside thepump body is equalized back tothe reservoir piping and the col-lected condensate in thereservoir pipe falls by gravity intothe pump body, starting the cycleall over again.

Because this system of con-densate removal and recovery isdesigned to be a “closed” system,there is no need for vacuumbreakers as we have used in thepast. In fact, the equipment isencouraged to work into a vacu-um condition if it is required bythe temperature control system.Even in vacuum conditions, con-densate is allowed to fall bygravity into the pump because thepump is equalized in pressure tothe outlet of the equipmentthrough the exhaust of the pump.

Waterhammer In CondensateReturn Lines

Waterhammer in condensatereturn lines is an indication of twopossible problems. In “open” sys-tems, atmospheric returns, thecauses of waterhammer are airpockets and/or steam traps dis-charging into a flooded section ofpiping. Air pockets in the line areeasily remedied by adding an airventing device for water systems,a float actuated device that willremain open until it is full of waterand air eliminated. Thesedevices are mounted on the highpoints of the return line and ventto atmosphere. Steam traps dis-charging into a water line shouldbe avoided at all costs.

As we mentioned earlier inthe flash steam recovery section,

condensate lines have historicallybeen sized for water volume onlyand not for the volume of flashsteam produced from traps dis-charging to a lower pressure. Ifthere is no other possible area todischarge a steam trap intoexcept a condensate return line,the installation shown aboveshould be followed. This breaksaway from the tradition of dis-charging steam traps intocondensate return lines at 90° tothe condensate return line by lit-erally injecting the steam trapdischarge into the condensatereturn line so that the actual out-let of the trap discharge is belowthe normal water level in thereturn line and discharging in thedirection of condensate flow.

This prevents sections offlash steam being trapped bywalls of water on both sideswhich, when steam condenses,causes a vacuum and violentlypulls the two walls of watertogether. These shock waves aretransmitted down the return pip-ing causing hammering noisesand pipe movement.

In “closed” systems, conden-sate return piping must be sizedfor two phase flow at low veloci-ties or the same situation willoccur.

Condensate Management

61

Figure 61Closed System

Figure 62Discharging Into Condensate Return Line

TemperatureControl Valve

Reservoir Piping

Air Vent

Condensate Return

Float &Thermostatic

Trap

PressurePoweredPump

Sparge Pipe

Enlarge Condensate return, if necessary, to accommodate Sparge Pipe

Sparge Puipe to made ofStainless Steel

Steam Utilization Course Review

62

1. Steam is created by _____________________ _________________________.

2. A typical target velocity for steam is ___________________________________.

3. Why is steam velocity important?

1. _________________________________________________________ _____

2. ______________________________________________________________

3. ______________________________________________________________

4. Four common rules in designing steam main drip stations are:

1. ______________________________________________________________

2. ______________________________________________________________

3. ______________________________________________________________

4. ______________________________________________________________

5. A normal byproduct of steam generation is the release of __________________.

6. How much condensate is created in a steam main of 8” diameter at 125 psig for

every 100 feet?____________________________________________________

7. What 3 categories do steam traps fall under?

1. ______________________________________________________________

2. ______________________________________________________________

3. ______________________________________________________________

8. List the types of steam traps for each category.

1. ______________________________________________________________

2. ______________________________________________________________

3. ______________________________________________________________

4. ______________________________________________________________

5. ______________________________________________________________

6. ______________________________________________________________

9. List the 4 methods used for testing steam traps.

1. ______________________________________________________________

2. ______________________________________________________________

3. ______________________________________________________________

4. ______________________________________________________________

10. When lifting condensate, how much pressure is exerted for every 2.3 feet of lift?

________________________________________________________________

Steam Utilization Course Review

63

11. Properly sized steam traps are sized to ____________________________ and not to

________________________________ ___________________________________.

12. How many tracer lines are recommended for an 8” product pipe to keep

temperatures at or above 150*F?

_____________________________________________________________________

13. Into what two groups can pressure reducing valves be divided?

1. ___________________________________________________________________

2. ___________________________________________________________________

14. What 3 factors attribute to proper reliability and accuracy of control valves?

1. ___________________________________________________________________

2. ___________________________________________________________________

3. ___________________________________________________________________

15. The term used when condensate is discharged to a lower pressure and partially

vaporizes is __________________________________________________________.

16. Calculate the percent of flash steam created when 100 psig condensate is

discharged to atmosphere (Sh L.P. - SH H.P.) ) Lh L.P.)

17. List 3 important reasons to recover condensate.

1. ___________________________________________________________________

2. ___________________________________________________________________

3. ___________________________________________________________________

18. List 3 considerations that must be met before flash steam recovery is viable and

economical.

1. ___________________________________________________________________

2. ___________________________________________________________________

3. ___________________________________________________________________

19. Condensate lines should be sized for handling what two factors?

1. ___________________________________________________________________

2. ___________________________________________________________________

20. Shock waves created in condensate return lines are known as

_____________________________________________________________________

64

Group Companies and Sales Offices

65

ArgentinaSpirax Sarco S.A.Ruta Panamericana Km. 24,9001611 Don TorcuatoBuenos Aires, ArgentinaAustraliaSpirax Sarco Pty. LimitedP.O. Box 6308Delivery CentreBlacktownN.S.W. 2148, AustraliaAustriaSpirax Sarco Ges.m.b.H.Eisgrubengasse 2/PF 41A-2334 Vosendorf-Sud.AustriaBelgiumSpirax Sarco N. V.Industriepark Zwijnaarde 59052 Gent - ZwijnaardeBelgiumBrazilSpirax Sarco Ind. E Com LtdaAv. Mancel Lages do ChaoCEP 06705-050Cotia S.P.Brazil

CanadaSpirax Sarco Canada Limited383 Applewood CrescentConcordOntario L4K 4J3, Canada

ChinaSpirax Sarco Engineering (China). Ltd.No. 107 Gui Qing RoadCaohejing Hi Tech ParkShanghai, China, Postcode 200233

ColombiaSpirax Sarco Internacional LtdaApartado Aereo 32484Cali (Valle)Colombia, South America

Czech RepublicSpirax Sarco Spol. s. r. o.V korytech (areal nakladoveho nadrazi CD)100 00 Praha 10 StrasniceCzech Republic

DenmarkSpirax Sarco LimitedBirkedommervej - 312400-Copenhagen N.V., Denmark

East AfricaSpirax Sarco Ltd(Above Gilami’s) Waryaki Way3rd Floor ABC PlaceWestlands, NairobiKenya, East Africa

FinlandSpirax OySorvaajankatu 900810 Helsinki, Finland

FranceSpirax Sarco S.A.B P 61F 78193 TrappesCedex, France

GermanySpirax Sarco GmbHPostfach 10 20 42D-78420 Konstanz, GermanyHygromatik Lufttechnischer Apparatebau GmbHLise-Meitner-StraBe 3D-24558 Henstedt-UlzburgGermanyGreat BritainSpirax Sarco LimitedHead OfficeCharlton House, CheltenhamGloucestershire, GL53 8ERGreat BritainHong KongSee SingaporeHungarySpirax Sarco Ltd.H-1141 BudapestOrs Vezer utja42HungaryIndiaSpirax Marshall LimitedP.B. No. 29Bombay Poona RoadKasarwadiPune 411 034, IndiaIndonesiaSee SingaporeItalySpirax-Jucker S.r.l.Via Per Cinisello 1820054 Nova MilaneseMilano, ItalyJapanSpirax Sarco (Japan) Limited2-37 HamadaMihamaku Chiba 261-0025JapanKoreaSpirax Sarco Korea Limited3rd-5th Floor, Jungwoo Building1552-8 Seocho-dongSeocho-kuSeoul 137-070, KoreaMalaysiaSpirax Sarco Sdn Bhd25, Jalan PJS 11/1Bandar Sunway46150 Petaling JayaSelangor Darul EhsanWest MalaysiaMexicoSpirax Sarco Mexicana S.A. de CVApartado Postal 196Santa Caterina, NL66350 - MexicoNew ZealandSpirax Sarco LimitedP.O. Box 76-160Manukau CityAuckland, New ZealandNigeriaSpirax Sarco Sales RepresentativeCakasa Company Ltd.96 Palm Ave.P.O. Box 871Mushin Lagos NigeriaNorwaySpirax Sarco Limited (Norge)P.O. Box 471483 Skytta, Norway

PakistanSpirax Sarco Sales Representative2-C Gulistan-E-Zafar P.R.E.C.H.S.Near SMCHS Block BPostal Code 74400Karachi, PakistanPolandSpirax Sarco Sp. z o.o.Fosa 2502-768 Warszawa, PolandPortugalSpirax Sarco-Equipamentos

Industrias Lda.Rua Da Quinta Do Pinheiro, 8Portela de Carnaxide2795 Carnaxide, PortugalRussiaSpirax Sarco Ltd.(Room 1401)4 Vozrozhdenija Str.198097 St. Petersburg, RussiaSingaporeSpirax Sarco Pvt. Limited464 Tagore Industrial AvenueUpper Thomson RoadSingapore 787833

South AfricaSpirax Sarco (Pty) Ltd.P.O. Box 925Kempton Park 1620Transvaal, South Africa

SpainSpirax Sarco S.A.Sant Josep, 130Poligon El Pla08980 Sant Feliu de LlobregatSpain

SwedenSpirax Sarco ABVästberga Allé 60S-126 30 Hagersten, Sweden

SwitzerlandSpirax Sarco A. G.Gustav-Maurer-Str.98702 Zollikon, Switzerland

TaiwanSpirax Longbridge Limited6th FloorNo. 8, Lane 94, Tsao Ti WeiShen Keng HsiangTaipei CountyTaiwan, Republic of China

ThailandSpirax Sarco Limited9th Floor, Benjaporn Building222 Krungtep-kreetha RoadBangkapiBangkok 10240, Thailand

U.S.A.Spirax Sarco, Inc.Northpoint Park1150 Northpoint Blvd.Blythewood, SC 29016

Watson-Marlow Bredel Inc.220 Balladvale StreetWilmington, MA 01887

VenezuelaSpirax Sarco S.A.Apartado 81088Caracas 1080A, Venezuela

Regional Offices

66

NORTHEASTNigel SewellColumbus, Ohio, Hub Office7760 Olentangy River RoadSuite 120Columbus, OH 43235Phone: (614) 436-8055Fax: (614) 436-8479

MID-ATLANTICEd Beedle4647 Saucon Creek RoadSuite 102Center City, PA 18034Phone: (610) 807-3500Fax: (610) 317-3279

SOUTHEASTBruce Moninghoff200 Centre Port DriveSuite 170Greensboro, NC 27409Phone: (336) 605-0221Fax: (336) 605-1719

MIDWESTPierre Schmidt2806 Centre Circle DriveDowners Grove, IL 60515Phone: (630) 268-0330Fax: (630) 268-0336

SOUTHWESTJon Lye203 Georgia Ave.Deer Park, TX 77536Phone: (281) 478-4002Fax: (281) 478-4615

WESTMike Gillick1930 East Carson Street, Suite 102Long Beach, CA 90810Phone: (310) 549-9962Fax: (310) 549-7909