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May 2007 19992007 Chevron USA Inc. All rights reserved. 300-1

300 Reciprocating Pumps

Abst rac t

This section discusses engineering principles, pump types, application and selection

criteria, and describes two commonly used reciprocating pumps. See Section 1100

for troubleshooting information.

Contents Page

310 Engineering Principles 300-2

320 Pump Types 300-4

321 Single and Double Acting Pumps

330 Application and Selection Criteria 300-7

331 Gas (Steam) Driven Pumps

332 Power Pumps

333 Sizing of Suction Lines

334 Selecting a Reciprocating Pump

CAUTION: Based upon the publication date, this document may not contain the latest

guidance. The user is strongly advised to contact the Technology Manual Sponsor to

determine the appropriate subject matter expert for consultation on applicability to the

users specific case.
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300 Reciprocating Pumps Pump Manual

300-2 19992007 Chevron USA Inc. All rights reserved. May 2007

310 Engineering Principles

A reciprocating pump is a positive displacement machine. It traps a fixed volume of

liquid at near-suction conditions, compresses it to discharge pressure, and pushes it

out the discharge nozzle. The basic principle involved is that a plunger or piston will

displace a quantity of liquid equal to its swept volume. In Figure 300-1, plunger A is

lowered into the container, displacing liquid which flows into container B. The

volume of liquid in container B is equal to the product of the cross-sectional area

of plunger A and the depth of immersion. In a reciprocating pump, the action of

plunger A is accomplished by a reciprocating piston, plunger, or diaphragm.

The fluid-handling section of a reciprocating pump is commonly called the liquid

end. The liquid end has a piston or plunger that displaces the fluid being pumped; a

close-fitting cylinder in which the piston travels; and suction and discharge valves

to admit and discharge the pumped fluid. Packing prevents liquid from leaking past

the rod attached to the piston, or, in a plunger pump, past the plunger.

Figure 300-2depicts the suction stroke of a plunger pump. When the plunger moves

away from the head end of the cylinder, the discharge check valve is held closed by

the higher pressure in the discharge pipe compared to the lower pressure in the

liquid cylinder. This lower pressure in the liquid cylinder also causes the suction

valve to be opened by the higher pressure in the suction line. Fluid then flows intothe cylinder until the plunger reaches the end of its travel.

Fig. 300-1 Reciprocating Pump Principles From Pump Handbook, (1976) Edited by Karassik,

Krutzch, Fraser & Messina. Used with permission from McGraw Hill.

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Pump Manual 300 Reciprocating Pumps


Figure 300-3depicts the discharge stroke of a plunger pump. As the plunger moves

toward the head end, the increasing pressure in the cylinder closes the suction valve.

The pressure in the cylinder continues to rise until it exceeds the pressure in the

discharge line and the discharge valve opens, releasing the volume of fluid

displaced by the plunger.

Unlike the centrifugal pump, which is a kinetic machine, the reciprocating pump

does not require velocity to achieve pressure. This is one of the reciprocating

pumps advantages, particularly for abrasive, slurry, and high-viscosity applica-

tions. High pressures can be obtained at low velocities, and fluid capacity varies

directly with pump speed.

The discharge pressure of a reciprocating pump is only that required to force the

desired volume of liquid through the discharge system. Within the constraints of

pump construction, the maximum pressure developed for gas-driven pumps is

limited only by the differential gas pressure available; for crank-driven pumps, the

driver torque is the only limit.

The flow of liquid from a reciprocating pump pulsates, varying both in flow rate and

pressure. As the piston or plunger moves back and forth in the cylinder, alternately

opening and closing the suction and discharge valves, a cyclic pulsation is set up in

the suction and discharge lines of the pump. Figure 300-4shows the changes in flow

rate as a function of crank angle for duplex, triplex, and quintuplex single-actingpumps. These changes become less severe as the number of stages increases.

Fig. 300-2 Plunger Pump Liquid End During Suction

Stroke From Pump Handbook, (1976) Edited

by Karassik, Krutzch, Fraser & Messina.

Used with permission from McGraw Hill.

Fig. 300-3 Plunger Pump Liquid End During Discharge

Stroke From Pump Handbook, (1976) Edited

by Karassik, Krutzch, Fraser & Messina.

Used with permission from McGraw Hill.

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Fig. 300-5 Typical Single- and Double-acting PumpsCourtesy of The Hydraulic Inst itute

Double-Acting Cylinder Pump

Vertical Single-Acting Plunger Power Pump

Horizontal Single-Acting Plunger Power Pump

Horizontal Double-Acting Piston Power Pump

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Reciprocating pumps are typically classified by:

1. Type of drive

a. Direct-acting, gas-driven

b. Crank-driven (power pumps)

2. Cylinder orientation

a. Horizontal

b. Vertical

3. Liquid end arrangement

a. Plunger (outside packing)

b. Piston (inside piston rings and packing on the piston rod)

c. Diaphragm (plunger or air pushing a flexible diaphragm)

4. Number of pistons or plungers

a. Simplex

b. Duplex

c. Triplex

d. Quintuplex, etc.

Fig. 300-6 Diaphragm Positive Displacement Pump (Shown here as Double Diaphragm posi-

tive Displacement Pump)

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5. Type of action

a. Single-acting (delivers on either forward or backward stroke, not both)

b. Double-acting (delivers on both forward and backward strokes)

Figure 300-7illustrates these classifications. (Metering pumps that use a recipro-cating motion are described in Section 500of this manual.)

321 Single and Double Acting Pumps

Single-acting pumps discharge on either the forward or return stroke of the piston or

plunger; every cycle of the pump displaces only one volume of liquid. In double-

acting pumps, liquid is discharged on both the forward and return stroke of the

piston. Plunger pumps are only single-acting; piston pumps can be either single- or

double-acting. Figure 300-5illustrates this pump action.

Simplex, Duplex, and Multip lex Pumps

The terms simplex, duplex, and multiplex refer to the number of piston-and-rod

assemblies in a pump. Simplex pumps have one piston-and-rod assembly; duplex

pumps have two; multiplex pumps have three or more.

330 Application and Selection Criteria

This section discusses selection of reciprocating pumps. With the accompanying

Pump Applications Guidelines, it will allow an individual to select pumps for most

services.

There is normally little problem in choosing between the two basic types of pumps,

direct-acting gas driven pumps and crank-driven power pumps. Gas driven pumps,

once the workhorse of the industry, are generally limited to utility functions by the

availability of compressed gas such as steam, air, or field gas. Power pumps, which

are motor, turbine, or engine driven, are available in a wide spectrum of capacities

and heads.

Fig. 300-7 Reciprocating Pump Sub-types Permission granted. Chemical Engineering,

September 21, 1981.

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331 Gas (Steam) Driven Pumps

Gas-driven pumps are commonly used for sump pump, transfer, low pressure boiler

feed, or relief drum pump-out. Although their speed and capacity are directly

affected by system pressures, gas driven pumps are of particular value when:

1. Electric power is not readily available or is unreliable.

2. A standby pump is required for use during electric power failures.

3. A wide capacity range, easily achieved by varying pump speed, is required.

4. Steam for pumping is available at little or no cost (when, for example, exhaust

steam from pumps is used to heat the pumped product).

Duplex gas pumps are more generally used than simplex because of their larger

capacity, smoother discharge, and simpler valve mechanism. Duplex pumps are also

made in a greater variety of sizes and types than are simplex pumps, which were

developed largely for vacuum or other low-pressure service.

The simplex is usually slightly more efficient than the duplex and has one less set ofpacking. Simplex pumps are usually preferable in vacuum or other services where

gas or vapor must be handled. Duplex pumps may short-stroke and fail to clear

themselves of vapor. In fact, they may vapor lock and come to a complete stall.

Because the simplex valve mechanism prevents short-stroking, close-clearance

pumps, designed especially to handle gas or vapor, are commonly made only in the

simplex type.

Reciprocating gas pumps range in size from a small 3 2.75 3-ft. pump, rated to

handle 23 gpm water, up to a 25 12 24-ft. pump capable of handling 1150 gpm

with a maximum liquid-end working pressure of 750 psi. Simplex pumps are ordi-

narily not made for capacities over about 500 gpm.

Selection of gas driven pumps requires attention to pump speed as it relates to the

required capacity in any given service. Figure 300-8shows the maximum recom-

mended piston speeds and corresponding revolutions per minute for direct-acting

gas pumps in various services. This figure represents the manufacturers recommen-

dation for maximum speed in these services. These speeds are acceptable for

standby or infrequently operated pumps, but should be reduced for pumps in contin-

uous service. For best operation, continuous duty pumps should be sized to run from

50 percent to 75 percent of the maximum speed shown on Figure 300-8.

See Figure 300-9for additional application guidelines.

Sizing of Steam Cylinders

When possible, steam-cylinder diameters should be selected based on the required

work. Oversizing steam cylinders permits overspeeding the pumps with greatly

increased wear and high maintenance costs. Steam consumption is increased and

there is the possibility of overpressure. If a steam cylinder of the proper size is

selected, overspeeding will be minimized and it will not be necessary to place a

relief valve on the pump discharge.

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300-9

Fig. 300-8 Maximum Recommended Speed and Capacity of Direct-Acting Gas Pumps

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On the other hand, steam cylinders should not be too small. An adequate allowance

should be made for tight packing, leaking valves, and other bad service conditions.

Such an adequate allowance will result if steam inlet pressure is taken as the

minimum pressure actually available at the inlet to the pump after making properallowance for piping and valve losses, and the mechanical efficiencies given below

are applied.

In general, the tendency is to make the liquid piston too small and the steam piston

too big with the result that the pump has no difficulty in meeting the required pres-

sure, but has to be overspeeded to meet its capacity. If the liquid piston is gener-

ously large, there is no incentive for the operator to overspeed the pump; and, if the

steam cylinder is not too large, it may be impossible to overspeed it.

A formula for estimating the required diameter of the steam-end cylinder is as

follows:

(Eq. 300-1)

Fig. 300-9 Reciprocating Pump Application Guidelines

Pu mp Des cr ipt io n Di rect A ct in g Po wer Pl un ger Po wer Pi sto n

Self Priming Y Y Y

Can Run Dry-Short Time Y Y Y

Will Emulsify N N N

Field Alignment Reqd N Y Y

Good for Some Entrained Gas Y Y Y

Good for Abrasives Y N Y

Parallel or Series Recommended P P P

Brgs Lub. (Oil, Grease, Stock) S O O

Coupling Rigid or Flexible N/A F F

Legend:

Y = yes, N = no

P = parallel

O = oil

S = stock

F = flexible

N/A = not applicable

Note: Pumps are commercially available outside the parameters shown. These pumps should be

avoided or, if they are used, special care should be taken to maintain reliability.

Ds2 DL

2

E----------

Pd Ps

Pi Pe-----------------=

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where:

Ds = Steam piston diameter, inches

DL = Liquid piston diameter, inches

Ps = Pump suction pressure, psig

Pd = Pump discharge pressure, psig

Pi = Steam inlet pressure, psig

Pe = Steam exhaust pressure, psig

E = Mechanical efficiency

Reduce above efficiencies by 1/10 if viscosity exceeds 4000 SSU or differential

pressure exceeds 300 psi.

Steam Consumption

The steam consumption of a steam-driven reciprocating pump may vary consider-

ably from one pump to another even though they are all identical in design and

under similar service conditions. The steam consumption will be affected by the

mechanical condition of the pump, the accuracy of the valve timing, the tightness of

the packing, etc. Figure 300-10illustrates how to determine the approximate steam

rate of direct-acting duplex-steam pumps in pounds per hydraulic horsepower hour.The steam rate of simplex pumps can be obtained by taking about 93% of that

obtained for a duplex pump. Figure 300-11illustrates the formula with applicable

notes corresponding to Figure 300-10.

A simple direct-acting steam pump cannot take any advantage of expansion of the

steam. Therefore, the steam rate is not materially reduced if steam pressures higher

than about 150 psi are used. Thermodynamically, it is better to take advantage of

expansion above this pressure in other equipment. Exhaust back pressure always

increases the steam rate materially.

Inlet steam pressure is not mentioned in the formula or the graph. The formula

assumes that enough initial steam pressure is available to do the required amount ofwork. This will be true if the steam cylinder is of the proper size. Steam pumps are

almost invariably operated with a hand or automatic valve, throttling the inlet steam

to provide the required pressure, and limit or regulate the speed.

Stroke Inches Approx. Eff.

Up to 6 .60

8 to 12 .70

Above 12 .75

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Fig. 300-11 Steam Rate of Direct-Acting Duplex Steam Pumps (1 of 2)

The following formula is very simple to use and will give a good approximation of the steam consumption of a simple

duplex steam pump in fair mechanical condition. Experience shows that under the most favorable circumstances,

some pumps do better, but that many with leaky valves or otherwise in poor condition do worse.

(Eq. 300-2)

where:

S = Total steam consumed, pounds per hour.

Q = Gallons per minute of liquid pumped.

P = Difference between suction and discharge pressure, in pounds per square inch.

es = Steam efficiency See table below.

Pb = Back pressure on exhaust pounds per square inch gage.

P = Friction m.e.p. referred to steam cylinder in lbs. per sq. in. See table below.

ev = Volumetric efficiency; usually over .95, and usually taken as 1.0 for rough figures; may be as low

as .5 for pumps in bad condition.

r = cylinder ratio, or ratio of area of the steam cylinder to the liquid cylinder.

Approx imate Steam Ef ficiency and Fr ic tion M.E.P.of Dup lex Steam Pumps

Stroke of pump 3" 4" 5" 6" 8" 10" 12" 15" 18" 24"

Steam eff., es .35 .375 .39 .40 .425 .45 .475 .50 .525 .55

Friction m.e.p., P

outside packed pumps

31.8 28.8 25.8 23.4 20.4 17.4 15.6 14.4 13.2 11.4

Ditto, inside packed pumps 30 27 24 21 18 15 13.5 12 10.5 9

Notes: Simplex steam pumpswill ordinarily have a steam efficiency from 7% to 10% higher than given for duplex pumps, largely

because they are built with smaller clearance and do not short-stroke when properly adjusted. The friction m.e.p. can be

markedly reduced by the use of high-class metallic packing.

Superheat .100of superheat will reduce steam consumption to 87%; 200will reduce it to 78% of that shown.

SQ

57.5esev

---------------------- P r Pb

P 18.5+ + + =

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332 Power Pumps

Crank driven power pumps are typically used in high pressure, low-to-moderateflowrate services on pipelines and in producing field applications such as water-

flood, mud pumps, and gathering systems.

Power pumps are divided into two common types; single-acting plunger and double-

or single-acting piston. Piston pumps are limited to approximately 1500 psig, but

plunger pumps typically go to 6000 psig and have been designed for discharges as

high as 30,000 psig.

Discussion

The formula given is sound theoretically, and the proper values of esand P will give true results. It is based

on the following assumptions:

1. Specific volume of steam in cylinder is

(Eq. 300-3)

cu. ft per lb., which holds well between 25# and 125# (gage).

where: Psis the available pressure in the steam line.

2. Gage pressure of steam in cylinder at end of stroke equals

(Eq. 300-4)

3. Steam efficiency is ratio of displacement of steam cylinder to steam actually used. The low efficiency invariablyfound is mainly due to the clearance volumewhich traps steam from the steam pipe to the exhaust pipe without

doing any work, and secondarily, to cylinder condensation. Valve leakage also plays a part. Although taken as a

constant, this efficiency is apt to vary considerably with conditions.

This formula shows the steam consumed, but does not showwhether the pump can actually perform the work

or not, either as regards capacity or pressure. The maximum pressure that the pump can put up is

theoretically

(Eq. 300-5)

However, at least a 25% additional margin of safety is desirable; the working pressure should be no more than

75% of that found above. The proper working capacity of a duplex pump in gallons per minute is

approximately

(Eq. 300-6)

where:

D = Diameter of liquid end, inches.

L = Length of stroke, inches.

Fig. 300-11 Steam Rate of Direct-Acting Duplex Steam Pumps (2 of 2)

460

Ps

18.5+----------------------

Ps

1

r---P P P

b+ +=

P r Ps

Pb

P =

Q10D

2L

L 10+-----------------=

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334 Selecting a Reciprocating Pump

The following steps may be used to select a reciprocating pump. For additional

guidance, see Section 2100.

1. Determine process duty.

2. Calculate liquid properties, if necessary.

3. Determine pipe pressure losses.

4. Calculate the suction head (same as for centrifugal pump).

5. Calculate the discharge head (same as for centrifugal pump).

6. Calculate the total head (same as for centrifugal pump).

7. Convert total head to pressure rise.

8. Calculate the NPSHA.

The expression for calculating the NPSHA for a reciprocating pump is similar

to that for a centrifugal pump except that acceleration head is included. Accel-

eration head is the force required to accelerate the fluid in the suction line. The

NPSHA for a reciprocating pump may be obtained as follows:

(Eq. 300-7)

Fig. 300-12 Suction Line Liquid Acceleration Head (ft) for Double-Acting Duplex Power Pumps

Average Suc tion Line

Velocity (fps)

Suction Line Acceleration Head for Suction Line Length (ft)

25 50 75 100

0.5 1.7 3.3 5.0 6.5

1.0 3.3 6.0 59.8 13.02.0 6.5 13.0 19.5 26.0

Notes: Refer to Section 130for a detailed discussion of acceleration head.

(1) For triplex pumps, use 57% of the values shown.

(2) For single-acting duplex and simplex pumps, use 174% of the values shown.

(3) Multiply values given above by the actual RPM divided by 60.

(4) Length of line is actual feet, not equivalent length. For pumps with suction stabilizers, length of line equals

10 pipe diameters.

(5) Acceleration head is added to the NPSH required by the pump.

(6) The NPSH requirement for a reciprocating pump, covering pressure loss from the inlet flange to the cylinder, is

primarily determined by the liquid velocity through the suction valve, the weight of the valve, spring loading on the

valve, and the liquid viscosity.(7) 12-ft NPSH allowance for a reciprocating gas pump is desirable.

(8) 8-ft to 10-ft NPSH is sufficient with some slower speed pumps.

(9) Special close clearance simplex pumps are available when some vaporization on the suction side may be expected.

(10)For hydrocarbons, use 75% of the values shown.

NPSHA hp hs hf hvpa hacc+=
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where:

hp = absolute pressure at suction source, e.g., a vessel (ft)

hs = static suction head (ft)

hf = friction head loss in suction piping including entrance losses (ft)

hvpa = vapor pressure of the fluid at pumping temperature (ft)

hacc = Acceleration head (ft)

(See Section 130for calculating acceleration head.)

9. Calculate brake horsepower.

(Eq. 300-8)

where:

GPM = Flow Rate in U.S. gallons per minute

psi = total differential pressure (pounds per square inch)

eff = pump efficiency (non-dimensional)

Note Use the following equation to convert head in feet to psi:

(Eq. 300-9)

where:

ht = Total head (ft)

SG = Specific gravity of liquid

10. Select particular pump.

Using the pump manufacturers literature and catalogs, select the pump for the

conditions obtained in the calculation. If possible, avoid selecting the largest

piston or plunger size for the pump case. Also avoid pumps which would have

to operate continuously at maximum allowable speed.

11. Consult pump Vendor.

Discuss pump selection with the Vendor for further recommendations and as a

check of the selection procedure.

12. Prepare pump data sheet and specification. See specification for reciprocating

pumps and API Specification 674.

BHP GPM psi 1715 eff =

psi ht SG 2.31=

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Pump Description Positive displacement-reciprocating-piston-duplex-direct acting-

gas driven (steam, air or process gas)

Typical Service Relief drum pumpout. Low pressure boiler feed. Water. Sludge.

Sump pump. Transfer.

Typical Pressure/Capacity Range 0700 psig/0500gpm

Max Allowable Temperature 350F

Typical Speed Range 30 to 60 RPM (with piston speeds usually between 50 and

100 FPM)

Construction Features Normal duplex, double acting, simplex available. Normally C. I.

steam and liquid ends with steel or bronze rods & trim

Typical Control Method Speed control by throttling drive gas (steam, air, process gas),

usually manual

Advantages Self priming. Will operate at very low speeds. High efficiency.Minimizes liquid emulsification. Handles viscous stocks. No elec-

trical power is required. Suitable for unattended remote installations

Disadvantages Pump speed is affected by system pressure. Subject to vapor lock

with low NPSH available. Will stall with too-high system back

pressure. Pulsating flow can affect sensitive instrumentation

downstream

Specification API 674. See also PMP-PC-1081 in this manual.

Data Sheet API 674, Appendix A. See also PMP-PC-1081 in this manual.

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Fig. 300-13 Duplex, Direct-acting, Gas-driven, Piston Reciprocating Pump

Part

No. Name of Part

Part

No. Name of part

Part

No. Name of Part

1 Steam Cylinder 10 Valve Rod 19 Valve Cover

2 Steam Cylinder Head 11 Valve Rod Lever 20 Valve Stem

3 Steam Piston 12 Liquid End Piston Rod 21 Valve Spring

4 Steam Piston Rings 13 Gland 22 Valve

5 Steam End Piston Rod 14 Gland Bushing 23 Valve Seat

6 Condensate Drain 15 Stuffing Box

7 Steam Chest 16 Liquid Piston

8 Slide Valve 17 Liquid Piston Rings9 Valve Rod Adjustment Nut 18 Cylinder Liner

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Pump Description Positive displacement-reciprocating-plunger (power pump)

Typical Service High pressure/low flow. Gathering systems/pipeline. Waterflood.

Drawing rig. Mud pumps. Well workover.

Typical Pressure/Capacity Range 5006000 psi/10600 gpm

Max Allowable Temperature 400F

Typical Speed Range 0450 RPM

Construction Features Vertical configurations available up to 200 HP. Available in duplex

through nonuplex, although triplex is most common. Crank driven

with motor, turbined with gearbox, or engine drivers. Steel liquid

end. Cast iron and steel power end. Self-contained lubrication

system.

Typical Control Method Variable speed or flow bypass

Advantages Higher pressures available than with piston pumps (up to 30,000 psi).

Self-priming. Constant delivery at high efficiency over wide pres-

sure range. Minimum fluid emulsification. Handles viscous stocks.

Can run dry for a limited time.

Disadvantages and Limitations Pulsing flow. Low capacity. High first cost and maintenance cost.

Low tolerance for abrasives. Subject to vapor lock at low suction

pressure with high vapor pressure stock.

Specification API 674. See also PMP-PC-1081 in this manual.

Data Sheet API 674, Appendix A. See also PMP-PC-1081 in this manual.

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Fig. 300-14 Reciprocating Plunger Power Pump Copyright 1995 Ingersol l Dresser Pumps. Worthington is a

trademark of Ingersoll Dresser Pump Company

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