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PRESSURE GAUGEINSTALLATION,OPERATION ANDMAINTENANCE
I&M008-10098-5/02 (250-1353H) 1M AMR 5P1/08
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CONTENTS1.0 Selection and Application
1.1 Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.3 Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.4 Oxidizing media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.5 Pulsation/Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.6 Gauge fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51.7 Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.0 Temperature2.1 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.2 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.3 Steam service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.4 Hot or very cold media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.5 Diaphragm seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.6 Autoclaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
3.0 Installation3.1 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73.2 Gauge reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73.3 Tightening of gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73.4 Process isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73.5 Surface mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73.6 Flush mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
4.0 Operation4.1 Frequency of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74.2 In-service inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74.3 When to check accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74.4 When to recalibrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74.5 Other considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84.6 Spare parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
5.0 Gauge Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
6.0 Accuracy: Procedures/Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-106.1 Calibration - Rotary movement gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116.2 Calibration - 1009 Duralife®Pressure Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116.3 Positive Pressure Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15
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CONTENTS
7.0 Diaphragm Seals7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.2 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.5 Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
8.0 Dampening Devices8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168.2 Throttle Screws & Plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.3 Ashcroft Gauge Saver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.4 Ashcroft Pulsation Dampener . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.5 Ashcroft Pressure Snubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.6 Campbell Micro-Bean® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.7 Ashcroft Needle Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178.8 Chemiquip® Pressure Limiting Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
9.0 Resources9.1 Training Videos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189.2 Pressure Instrument Testing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189.3 Tools & Tool Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
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Cover photo courtesy of Johnson/Yokogawa Co.
Campbell Micro-Bean® is a registered trademark of J.A. Campbell Co.
Chemiquip® is a registered trademark of Chemiquip Products Co. Inc.
1.0 SELECTION & APPLICATIONUsers should become familiar with ASMEB40.1 (Gauges – Pressure Indicating DialType – Elastic Element) before specifyingpressure measuring instruments. That docu-ment – containing valuable informationregarding gauge construction, accuracy, safety,selection and testing – may be ordered from:
ASME InternationalThree Park AvenueNew York, N.Y. 10016-5990800-843-2763 (US/Canada)95-800-843-2763 (Mexico)973-882-1167 outside North AmericaEmail: [email protected]
WARNING: To prevent misapplication, pres-sure gauges should be selected consideringmedia and ambient operating conditions.Improper application can be detrimental to thegauge, causing failure and possible personalinjury, property damage or death. The infor-mation contained in this manual is offered asa guide in making the proper selection of apressure gauge. Additional information isavailable from Ashcroft Inc.
The following is a highlight of some of the moreimportant considerations:
1.1 Range – The range of the instrumentshould be approximately twice the maximumoperating pressure. Too low a range mayresult in (a) low fatigue life of the elastic ele-ment due to high operating stress and (b) sus-ceptibility to overpressure set due to pressuretransients that exceed the normal operatingpressure. Too high a range may yield insuffi-cient resolution for the application.
1.2 Temperature – Refer to page 6 of thismanual for important information concerningtemperature related limitations of pressuregauges, both dry and liquid filled.
1.3 Media – Thematerial of the process sensingelement must be compatible with the processmedia.Use of a dia-phragm seal with the gaugeis recommended for process media that (a) arecorrosive to the process sensing element; (b)
contain heavy particulates (slurries) or (c) arevery viscous including those that harden atroom temperature.
1.4 Oxidizing media – Gauges for direct useon oxidizing media should be speciallycleaned. Gauges for oxygen service should beordered to variation X6B and will carry theASME required dial marking “USE NO OIL”in red letters. Gauges for direct use on otheroxidizing media may be ordered to variationX6W. They will be cleaned but carry no dialmarking. Plus!® gauges or Halocarbon filledgauge or diaphragm fill is required for usewith oxidizing media; order variation XCF.
1.5 Pulsation/Vibration – Pressure pulsationcan be dampened by several mechanisms; thepatented PLUS! Performance gauge will han-dle the vast majority of applications. Oneexception to this is high frequency pulsationwhich is difficult to detect. The only indicationmay be an upscale zero shift due to movementwear. These applications should be addressedwith a liquid filled gauge, or in extreme cases,a remotely mounted liquid filled gauge con-nected with a length of capillary line. Thesmall diameter of the capillary provides excel-lent dampening, but can be plugged. TheAshcroft 1106 pulsation dampener and 112snubber are auxiliary devices which dampenpulsation with less tendency to plug.
1.6 Gauge fills. – Once it has been determinedthat a liquid filled gauge is in order, the nextstep is selecting the type of fill.Glycerin sat-isfies most applications.While being the leastexpensive fill, its usable temperature range is20/250°F. Silicone filled gauges have abroader service range: –40/250°F. Oxidizingmedia require the use of Halocarbon, with aservice range of –50/250°F. Pointer motionwill be slowed at the low end of the low end ofthese temperature ranges.
1.7 Mounting – Users should predeterminehow the gauge will be mounted in service:stem (pipe), wall (surface) or panel (flush).Ashcroft wall or panel mounting kits should beordered with the gauge. See paragraph 3Installation.
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2.0 TEMPERATURE2.1 Ambient Temperature – To ensure longlife and accuracy, pressure gauges shouldpreferably be used at an ambient tempera-ture between –20 and +150F (–30 to +65C).Atvery low temperatures, standard gauges mayexhibit slow pointer response.Above 150F, theaccuracy will be affected by approximately1.5% per 100F. Other than discoloration of thedial and hardening of the gasketing, non-liq-uid filled type 1279 (phenolic case) and 1379(aluminum case) Duragauge®, with standardglass windows, and Duralife® gauges types1008 and 1009, can withstand continuousoperating temperatures up to 250F. Liquidfilled gauges can withstand 200F but glycerinfill and the acrylic window of Duragauge®
gauges will tend to yellow. Silicone fill willhave much less tendency to yellow. Low pres-sure, liquid filled types 1008 and 1009 gaugesmay have some downscale errors caused byliquid fill expansion. This can be alleviated by“burping” the gauge by gently pushing the topfill plug to one side to admit air to the case.
Although the gauge may be destroyed and cal-ibration lost, gauges can withstand shorttimes at the following temperatures: gaugeswith all welded pressure boundary joints,750F (400C); gauges with silver brazed joints,450F (232C) and gauges with soft solderedjoints, 250F (121C). For expected long termservice below –20F (–30C) Duragauge® and41⁄2˝ 1009 gauges should be hermeticallysealed and specially lubricated; add “H” to theproduct code for hermetic sealing. Add varia-tion XVY for special lubricant. StandardDuralife gauges may be used to –50F (–45C)without modification.
2.2 Accuracy – Heat and cold affect accuracyof indication. A general rule of thumb for drygauges is 0.5% of full scale change for every40°F change from 75°F. Double that allowancefor gauges with hermetically sealed or liquidfilled cases, except for Duragauge® gaugeswhere no extra allowance is required due tothe elastomeric, compensating back. Above250°F there may exist very significant errorsin indication.
2.3 Steam service – In order to prevent livesteam from entering the Bourdon tube, asiphon filled with water should be installedbetween the gauge and the process line.Siphons can be supplied with ratings up to4,000 psi. If freezing of the condensate in theloop of the siphon is a possibility, a diaphragmseal should be used to isolate the gauge fromthe process steam. Siphons should also beused whenever condensing, hot vapors (notjust steam) are present. Super heated steamshould have enough piping or capillary lineahead of the siphon to maintain liquid waterin the siphon loop.
2.4 Hot or very cold media – A five foot capil-lary line assembly will bring most hot or coldprocess media within the recommended gaugeambient temperature range. For media above750F (400C) the customer should use his ownsmall diameter piping to avoid possible corro-sion of the stainless steel.The five foot capillarywill protect the gauges used on the commoncryogenic (less than –300F (200C) gases, liquidargon, nitrogen, and oxygen. The capillary andgauge must be cleaned for oxygen service. Themedia must not be corrosive to stainless steel,andmust not plug the small bore of the capillary.
2.5 Diaphragm seals – As mentioned above, adiaphragm seal should be used to protectgauges from corrosive media, or media thatwill plug the instrument. Diaphragm sealsare offered in a wide variety of designs andcorrosion resistant materials to accommodatealmost any application and most connections.Request bulletin OH-1 for details.
2.6 Autoclaving – Sanitary gauges withclamp type connections are frequently steamsterilized in an autoclave. Gauges equippedwith polysulfone windows will withstandmore autoclave cycles than those equippedwith polycarbonate windows. Gaugesequipped with plain glass or laminated safetyglass should not be autoclaved. Gaugecases should be vented to atmosphere (remov-ing the rubber fill/safety plug if necessary)before autoclaving to prevent the plasticwindow from cracking or excessively distort-ing. If the gauge is liquid filled, the fill should
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also be drained from the case and the front ringloosened before autoclaving.
3.0 INSTALLATION
3.1 Location – Whenever possible, gaugesshould be located to minimize the effects ofvibration, extreme ambient temperatures andmoisture. Dry locations away from very highthermal sources (ovens, boilers etc.) are pre-ferred. If the mechanical vibration level isextreme, the gauge should be remotely locat-ed (usually on a wall) and connected to thepressure source via flexible tubing.
3.2 Gauge reuse – ASME B40.1 recommendsthat gauges not be moved indiscriminatelyfrom one application to another. The cumula-tive number of pressure cycles on an in-serviceor previously used gauge is generallyunknown, so it is generally safer to install anew gauge whenever and wherever possible.This will also minimize the possibility of areaction with previous media.
3.3 Tightening of gauge – Torque shouldnever be applied to the gauge case. Instead,an open end or adjustable wrench shouldalways be used on the wrench flats of thegauge socket to tighten the gauge into the fit-ting or pipe. NPT threads require the use of asuitable thread sealant, such as pipe dope orteflon tape, and must be tightened verysecurely to ensure a leak tight seal.
CAUTION: Torque applied to a diaphragmseal or its attached gauge, that tends to loosenone relative to the other, can cause loss of filland subsequent inaccurate readings. Alwaysapply torque only to the wrench flats on thelower seal housing when installing filled,diaphragm seal assemblies or removing samefrom process lines.
3.4 Process isolation – A shut-off valveshould be installed between the gauge andthe process in order to be able to isolate thegauge for inspection or replacement withoutshutting down the process.
3.5 Surface mounting – Also known as wall
mounting. Gauges should be kept free of pipingstrains.The gauge casemounting feet, if applic-able, will ensure clearance between the pres-sure relieving back and the mounting surface.
3.6 Flush mounting – Also known as panelmounting. The applicable panel mountingcutout dimensions can be found atwww.ashcroft.com
4.0 OPERATION
4.1 Frequency of inspection – This is quitesubjective and depends upon the severity ofthe service and how critical the accuracy ofthe indicated pressure is. For example, amonthly inspection frequency may be in orderfor critical, severe service applications.Annual inspections, or even less frequentschedules, are often employed in non-criticalapplications.
4.2 In-service inspection – If the accuracy ofthe gauge cannot be checked in place, the usercan at least look for (a) erratic or randompointer motion; (b) readings that are suspect– especially indications of pressure when theuser believes the true pressure is 0 psig. Anygauge which is obviously not working or indi-cating erroneously, should be immediatelyvalved-off or removed from service to avoid apossible pressure boundary failure.
4.3When to check accuracy – Obviously anysuspicious behavior of the gauge pointer war-rants a full accuracy check be performed.Even if the gauge is not showing any symp-toms of abnormal performance, the user maywant to establish a frequency of bench typeinspection.
4.4When to recalibrate – This depends on thecriticality of the application. If the accuracy ofa 3-2-3% commercial type gauge is only 0.5%beyond specification, the user must decidewhether it’s worth the time and expense tobring the gauge back into specification.Conversely if the accuracy of a 0.25% testgauge is found to be 0.1% out of specificationthen obviously the gauge should be recalibrat-ed.
4.5 Other considerations – These include (a)bent or unattached pointers due to extremepressure pulsation; (b) broken windows whichshould be replaced to keep dirt out of theinternals; (c) leakage of gauge fill; (d) casedamage – dents and/or cracks; (e) any signs ofservice media leakage through the gaugeincluding its connection; (f) discoloration ofgauge fill that impedes readability.
4.6 Spare parts – As a general rule it is rec-ommended that the user maintain in hisparts inventory one complete Ashcroft®
instrument for every ten (or fraction thereof)of that instrument type in service.
5.0 GAUGE REPLACEMENT
It is recommended that the user stock onecomplete Ashcroft® instrument for every ten(or fraction thereof) of that instrument type inservice. With regard to gauges having a ser-vice history, consideration should be given todiscarding rather than repairing them.Gauges in this category include the following:
a. Gauges that exhibit a span shift greaterthan 10%. It is possible the Bourdon tubehas suffered thinning of its walls by corro-sion.
b. Gauges that exhibit a zero shift greaterthan 25%. It is likely the Bourdon tubehas seen significant overpressure leavingresidual stresses that may be detrimentalto the application.
c. Gauges which have accumulated over1,000,000 pressure cycles with significantpointer excursion.
d. Gauges showing any signs of corrosionand/or leakage of the pressure system.
e. Gauges which have been exposed to hightemperature or simply exhibit signs ofhaving been exposed to high temperature– specifically 250°F or greater for soft sol-dered systems; 450°F or greater for brazedsystems; and 750°F or greater for weldedsystems.
f. Gauges showing significant friction errorand/or wear of the movement and linkage.
g. Gauges having damaged sockets, especiallydamaged threads.
h. Liquid filled gauges showing loss of casefill.
NOTE: ASME B40.1 does not recommendmoving gauges from one application to anoth-er. This policy is prudent in that it encouragesthe user to procure a new gauge, properly tai-lored by specification, to each application thatarises.
6.0 ACCURACY:PROCEDURES/DEFINITIONS
Accuracy inspection – Readings at approxi-mately five points equally spaced over thedial should be taken, both upscale and down-scale, before and after lightly rapping thegauge to remove friction. A pressure standardwith accuracy at least 4 times greater thanthe accuracy of the gauge being tested is rec-ommended.
Equipment – A finely regulated pressure sup-ply will be required. It is critical that the pip-ing system associated with the test setup beleaktight. The gauge under test should bepositioned as it will be in service to eliminatepositional errors due to gravity.
Method – ASME B40.1 recommends thatknown pressure (based on the reading fromthe pressure standard used) be applied to thegauge under test. Readings including anyerror from the nominal input pressure, arethen taken from the gauge under test. Thepractice of aligning the pointer of the gaugeunder test with a dial graduation and thenreading the error from the master gauge(“reverse reading”) can result in inconsistentand misleading data and should NOT be used.
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Calibration chart – After recording all of thereadings it is necessary to calculate the errorsassociated with each test point using the fol-lowing formula: ERROR in percent = 100times (TRUE VALUE minus READING) ÷RANGE. Plotting the individual errors(Figure 1 on page 10) makes it possible tovisualize the total gauge characteristic. Theplot should contain all four curves: upscale –before rap; upscale – after rap; downscale –before rap; downscale – after rap. Rap meanslightly tapping the gauge before reading toremove friction as described in ASME B40.1.
Referring to Figure 1 on page 10, severalclasses of error may be seen:
Zero – An error which is approximately equalover the entire scale. This error can be mani-fested when either the gauge is dropped oroverpressured and the bourdon tube takes apermanent set. This error may often be cor-rected by simply repositioning the pointer.Except for test gauges, it is recommendedthat the pointer be set at midscale pressure to“split” the errors.
Span – A span error exists when the error atfull scale pressure is different from the errorat zero pressure. This error is often propor-tional to the applied pressure. Most Ashcroftgauges are equipped with an internal, adjust-ing mechanism with which the user can cor-rect any span errors which have developed inservice.
Linearity – A gauge that has been properlyspanned can still be out of specification at
intermediate points if the response of thegauge as seen in Figure 1 on page 10 is notlinear. The Ashcroft Duragauge® pressuregauge is equipped with a rotary movementfeature which permits the user to minimizethis class of error. Other Ashcroft gaugedesigns (e.g., 1009 Duralife®) require that thedial be moved left or right prior to tighteningthe dial screws.
Hysteresis – Some Bourdon tubes have amaterial property known as hysteresis. Thismaterial characteristic results in differencesbetween the upscale and downscale curves.This class of error can not be eliminatedby adjusting the gauge movement or dialposition.
Friction – This error is defined as the differ-ence in readings before and after lightly tap-ping the gauge case at a check point. Possiblecauses of friction are burrs or foreign materi-al in the movement gearing, “bound” linkagesbetween the movement and the bourdon tube,or an improperly tensioned hairspring. If cor-recting these potential causes of friction doesnot eliminate excessive friction error, themovement should be replaced.
(Continued on page 10)
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TYPICAL CALIBRATION CHARTINDICATED VALUE (PSI)
True Value – Increasing – Increasing – Decreasing – Decreasing –PSI Without RAP With RAP Without RAP With RAP
0 –.4 0 –.4 040 +.8 +1.0 +1.4 +1.180 +.4 +.5 +1.2 +1.0120 –.4 –1.0 +.8 +.6160 –.8 –.5 +.6 +.4200 +.4 +.8 +.4 +.4
ERROR (% OF FULL SCALE)
True Value – Increasing – Increasing – Decreasing – Decreasing –% of Range Without RAP With RAP Without RAP With RAP
0 –.20 0 –.20 020 +.40 +.50 +.70 +.5540 +.20 +.25 +.60 +.5060 –.20 –.05 +.40 +.3080 –.40 –.25 +.30 +.20100 +.20 +.40 +.20 +.20
1.0
0.5
0.0
–0.5
–1.0
0 20 40 60 80 100% of Range
�
�
�
�
�
�
��
�
�
�
�
�
�
�
�
�
�
�
�
� � upscale – without rap
� � upscale – with rap
� � downscale – without rap
� � downscale – with rap
Error(%
ofFullScale)
Fig. 1
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6.1 Calibration – Rotary Movement Gauges– Inspect gauge for accuracy. Many timesgauges are simply “off zero” and a simplepointer adjustment using the micrometerpointer is adequate. If inspection shows thegauge warrants recalibration to correct spanand/or linearity errors, proceed as follows:
a. Remove ring, window and, if solid frontcase, the rear closure assembly.
b. Pressurize the gauge once to full scale andback to zero.
c. Refer to Figure 2 on page 8 for a view of atypical Ashcroft system assembly withcomponent parts identified.
d. For solid front gauges, adjust the microme-ter pointer so that it rests at the true zeroposition. For open front gauges the pointerand dial must also be disassembled andthe pointer should then be lightly pressedonto the pinion at the 9:00 o’clock position.
e. Apply full scale pressure and note themagnitude of the span error. With openfront gauges, ideal span (270 degrees) willexist when at full scale pressure the point-er rests exactly at the 6:00 o’clock position.
f. If the span has shifted significantly (spanerror greater than 10%), the gauge shouldbe replaced because there may be somepartial corrosion inside the bourdon tubewhich could lead to ultimate failure. If thespan error exceeds 0.25%, loosen the lowerlink screw and move the lower end of thelink toward the movement to increasespan or away to decrease span. An adjust-ment of 0.004 inch will change the span byapproximately 1%. This is a repetitive pro-cedure which often requires more than oneadjustment of the link position and thesubsequent rechecking of the errors at zeroand full scale pressure.
g. Apply midscale pressure and note error inreading. Even though the gauge is accu-rate at zero and full scale, it may be inac-curate at the midpoint. This is called lin-earity error and is minimized by rotatingthe movement. If the error is positive, the
movement should be rotated counter clock-wise. Rotating the movement one degreewill change this error by approximately0.25%. Rotating the movement oftenaffects span and it should be subsequentlyrechecked and readjusted if necessaryaccording to step 6.1e and 6.1f.
h. While recalibrating the gauge, the frictionerror – difference in readings taken withand without rap – should be noted. Thiserror should not exceed the basic accuracyof the gauge. If the friction error is exces-sive, the movement should be replaced.One possible cause of excessive friction isimproper adjustment of the hairspring.The hairspring torque,or tension, must beadequate without being excessive. Thehairspring should also be level, unwindevenly (no turns rubbing) and it shouldnever tangle.
NOTES:1 For operation of test gauge external zeroreset, refer to Figure 3 on page 12.
2 For test gauge calibration procedure,refer to Figure 4 on page 13.
6.2 Calibration – 1009 Duralife® Gauge –Inspect gauge for accuracy. Many timesgauges are simply “off zero” and a simplepointer adjustment using the adjustablepointer is adequate. If the inspection showsthat the gauge warrants recalibration to cor-rect span and/or linearity errors, proceed asfollows:
Remove ring, window, gasket and pointerusing Ashcroft tool kits 1205T and 1206T.
6.3 Positive Pressure Ranges –
a. Remove dial and lightly press pointer ontopinion at 9:00 o’clock position.
b. Apply full scale pressure and rotate spanblock as shown in Figure 5a on page 15until pointer rests at 6:00 o’clock position.
c. Fully exhaust pressure and check thatpointer still is at 9:00 o’clock position. Ifnot repeat steps 1 and 2 until span iscorrect.
(Continued on page 10)
12
BOURDON TUBESEGMENT
TIP
LINK
BACKPLATE
SOCKET
ROTARY MOVEMENT
PINION
HAIRSPRING
Fig. 2
TYPE 1082 EXTERNAL ZERO ADJUST FEATURE*
ARING
INSTRUCTIONS FOR USE:LOOSEN RING LOCKING SCREW “A’’OBTAIN REQUIRED ADJUSTMENT BY ROTATINGKNOB “B’’ CLOCKWISE OR COUNTER-CLOCKWISE.TIGHTEN SCREW “A’’ DOWN ON KNOB “B.’’
*Applicable only for test gauge with hinged ring design.
B
ASHCROFT SYSTEM ASSEMBLY
Fig. 3
13
TYPE 1082 TEST GAUGE CALIBRATION PROCEDUREFig. 4
14
d. Remove pointer and reassemble dial anddial screws (finger tight).
e. Lightly press pointer onto pinion.
f. Check accuracy at full scale. If error exceeds1% return to step 1, otherwise proceed.
g. Check accuracy at midscale. If error exceeds1% slide dial left or right to compensate.
h. Continue at * below.Vacuum range –
a. Using a pencil, refer to dial and mark the0 and 25 inch of Hg positions on the caseflange.
b. Remove the dial.
c. Apply 25 inches of Hg vacuum.
d. Lightly press pointer onto pinion carefullyaligning it with the 25 inch of Hg vacuummark on case flange.
e. Release vacuum fully.
f. Note agreement of pointer to zero mark oncase flange.
g. If span is high or low, turn span block asshown in Figure 5b on page 15.
h. Repeat steps 4 through 8 until span iscorrect.
i. Remove the pointer.
j. With 25 inches of Hg vacuum applied,reassemble dial, dial screws (finger tight)and pointer.
k. Apply 15 inches of Hg vacuum and noteaccuracy of indication. If required, slide dialleft or right to reduce error to 1%maximum.
l. Continue at * below.*Now complete calibration of the gauge asfollows:
a. Firmly tighten dial screws.
b. Firmly tap pointer onto pinion, using brassback-up tool from Ashcroft kit 1205T ifgauge has rear blow-out plug. If gauge hastop fill hole no back-up is required.
c. Recheck accuracy at zero, midscale and fullscale points (Figures 5a & 5b on page 15).
d. Reassemble window, gasket and ring.
15
25
V
s
1009 DURALIFE® PRESSURE GAUGE CALIBRATION
16
7.0 DIAPHRAGM SEALS
7.1 General – A diaphragm seal (isolator) is adevice which is attached to the inlet connec-tion of a pressure instrument to isolate itsmeasuring element from the process media.The space between the diaphragm and theinstrument’s pressure sensing element issolidly filled with a suitable liquid.Displacement of the liquid fill in the pressureelement, through movement of thediaphragm, transmits process pressurechanges directly to a gauge, switch or anyother pressure instrument. When diaphragmseals are used with pressure gauges, an addi-tional 0.5% tolerance must be added to thegauge accuracy because of the diaphragmspring rate.
Used in a variety of process applicationswhere corrosives, slurries or viscous fluidsmay be encountered, the diaphragm sealaffords protection to the instrument where:
• The process fluid being measured wouldnormally clog the pressure element.
• Pressure element materials capable ofwithstanding corrosive effects of certainfluids are not available.
• The process fluid might freeze due tochanges in ambient temperature and dam-age the element.
7.2 Installation – Refer to sales bulletin OH-1for information regarding (a) seal configura-tions; (b) filling fluids; (c) temperature rangeof filling fluids; (d) diaphragm material pres-sure and temperature limits; (e) bottom hous-ing material pressure and temperature lim-its; (f) pressure rating of seal assembly; (g)accuracy/temperature errors of seal assembly;(h) diaphragm seal displacement. The volu-metric displacement of the diaphragm mustat least equal the volumetric displacement ofthe measuring element in the pressureinstrument to which the seal is to be attached.
It is imperative that the pressure instru-ment/diaphragm seal assembly be properly
filled prior to being placed in service. Ashcroftdiaphragm seal assemblies should only befilled by a seal assembler certified by AshcroftInc. Refer to section 3.3 for a cautionary noteabout not applying torque on either theinstrument or seal relative to the other.
7.3 Operation – All Ashcroft® diaphragmseals, with the exception of Type 310 mini-seals, are continuous duty. Should the pres-sure instrument fail, or be removed acciden-tally or deliberately, the diaphragm will seatagainst a matching surface preventing dam-age to the diaphragm or leakage of theprocess fluid.
7.4 Maintenance – Clamp type diaphragmseals – Types 100, 200 and 300 – allow forreplacement of the diaphragm or diaphragmcapsule, if that ever becomes necessary. TheType 200 top housing must also be replacedwith the diaphragm. With all three types theclamping arrangement allows field disassem-bly to permit cleaning of the seal interior.
7.5 Failures – Diaphragm failures are gener-ally caused by either corrosion, high tempera-tures or fill leakage. Process media build-upon the process side of the diaphragm can alsorequire seal cleaning or replacement. ConsultCustomer Service, Stratford CT for advice onseal failures and/or replacement.
WARNING: All seal components should beselected considering process and ambientoperating conditions to prevent misapplica-tion. Improper application could result in fail-ure, possible personal injury, propertydamage or death.
8.0 DAMPENING DEVICES
8.1 General – Some type of dampening deviceshould be used whenever the pressure gaugemay be exposed to repetitive pressure fluctu-ations that are fairly rapid, high in magni-tude and especially when transitory pressurespikes exceeding the gauge range are present(as with starting and stopping action of valvesand pumps). A restricted orifice of some kindis employed through which pressure fluctua-
17
tions must pass before they reach the bourdontube. The dampener reduces the magnitude ofthe pressure pulse thus extending the life ofthe Bourdon tube and movement. This reduc-tion of the pressure pulsation as “seen” by thepressure gauge is generally evidenced by areduction in the pointer travel. If the orifice isvery small the pointer may indicate the aver-age service pressure, with little or no indica-tion of the time varying component of theprocess pressure.
Commonly encountered media (e.g. – waterand hydraulic oil) often carry impuritieswhich can plug the orifice over time thus ren-dering the gauge inoperative until the damp-ener is cleaned or replaced.
Highly viscous media and media that tend toperiodically harden (e.g., asphalt) require adiaphragm seal be fitted to the gauge. Theseal contains an internal orifice which damp-ens the pressure fluctuation within the fillfluid.
8.2 Throttle Screws & Plugs – These acces-sories provide dampening for the least cost.They have the advantage of fitting completelywithin the gauge socket and come in threetypes: (a) a screwed-in type which permitseasy removal for cleaning or replacement; (b)a pressed in, non-threaded design and (c) apressed in, threaded design which provides ahighly restrictive, helical flow path. Not allstyles are available on all gauge types.
8.3 Ashcroft Gauge Saver – Type 1073Ashcroft gauge saver features an elastomericbulb that fully isolates the process mediafrom the bourdon tube. In addition to provid-ing dampening of pressure pulses, the bour-don tube is protected from plugging and cor-rosion. The space between the bulb and bour-don tube is completely filled with glycerin.Felt plugs located between the bulb and bour-don tube are first compressed some amount torestrict the flow of glycerin through an orificeand thus provide a degree of dampening. Thegreater the compression of the felts thegreater the degree of dampening.
8.4 Ashcroft Pulsation Dampener – Type1106 Ashcroft pulsation dampener is a mov-ing pin type in which the restricted orifice isthe clearance between the pin and any one offive preselected hole diameters. Unlike a sim-ple throttle screw/plug, this device has a self-cleaning action in that the pin moves up anddown under the influence of pressure fluc-tuations.
8.5 Ashcroft Pressure Snubber – The heartof the Type 1112 pressure snubber is a thickporous metal filter disc. The disc is availablein four standard porosity grades.
8.6 Campbell Micro-Bean® – Type 1110Micro-Bean is a precision, stainless steel, nee-dle valve instantly adjustable to changingconditions of flow and viscosity. A very slighttaper on the valve stem fits into tapered holein the body. The degree of dampening is easi-ly adjusted by turning the valve handle. A fil-ter is built into the Micro-Bean to help pre-vent plugging.
8.7 Ashcroft Needle Valves – Type 7001 thru7004 steel needle valves provide varyingdegrees of dampening similar to the CampbellMicro-Bean but with a less precise and lesscostly adjustability. Like the Micro-Beanthese devices, in the event of plugging, caneasily be opened to allow the pressure fluid toclear away the obstruction.
8.8 Chemiquip® Pressure Limiting Valves –Model PLV-255, PLV-2550, PLV-5460, PLV-5500 and PLV-6430, available with and with-out built-in snubbers, automatically “shut off”at adjustable preset values of pressure to pro-tect the gauge from damage to overpressure.They are especially useful on hydraulic sys-tems wherein hydraulic transients (spikes)are common.
18
9.0 RESOURCES9.1 Training Videos
9.1.1 Test gauge calibration9.1.2 1009 Duralife® gauge calibration9.1.3 Duragauge® gauge calibration9.1.4 Diaphragm seal filling
9.2 Pressure InstrumentTesting Equipment9.2.1 Type 1305D Deadweight Tester9.2.2 Type 1327D Pressure Gauge Comparator9.2.3 Type 1327CM “Precision” Gauge Comparator
9.3 Tools & Tool Kits9.3.1 Type 2505 universal carrying case for 1082 test gauge9.3.2 Type 266A132-01 span wrench for 1082 test gauge9.3.3 Type 1280 conversion kit for 41⁄2˝ lower connect 1279/13799.3.4 Type 1283 conversion kit for 41⁄2˝ back connect 1279/13799.3.5 Type 1284 conversion kit for 6˝ lower & back connect9.3.6 Type 1281 socket O-Ring kit for 1279/1379 lower connect9.3.7 Type 1285 41⁄2˝ ring wrench for 1279/1379 lower & back connect9.3.8 Type 1286 6˝ ring wrench for 1379 lower & back connect9.3.9 Type 1287 cone tool for installing diaphragm & spring on 1279/1379 back connect9.3.10 Type 1105T calibration tool kit (all gauges except 1009 Duralife®)9.3.11 Type 3220 pointer puller (all gauges except 1009 Duralife®)9.3.12 Type. 3530 pinion back-up tool for 1009 Duralife®
9.3.13 Type 1230 throttle plug insertion (1⁄4 NPT) for 1009 Duralife®
9.3.14 Type 1231 throttle plug insertion (1⁄2 NPT) for 1009 Duralife® (body only)9.3.15 Type 1205T calibration hand tools for 1009 Duralife®
9.3.16 Type 1206T ring removal & assembly tools for 1009 Duralife
