ASME B40.5:1995 pdf download Snubbers
SCOPE
This Standard is confined to devices that are in-stalled between the pressure source and the pressurcsensing element and are used to minimize the effectof pressure surges on positive and negative pressuresensine instruments.
2 PURPOSE
These devices commonly known as snubbers, pul-sation dampeners,pressure equalizers,eauge protec-tors,gauge savers,etc.,are used toimprovetheoutputor rcadabillty of the instrument, and to reduce theeffect of pressure surges on the instrument. They alsolimit the cxternal discharge of the pressure medium,in the event a discontinuity should occur on the in-strument side of the snubber.
3 GENERAL
3.1 Terminology Defined
Terms relevant to this Standard and its applicationare as follows:
response time – the time required for a change insystem pressurc to be indicated by the instrummentsurge — a sudden rise or drop in system pressurepulsation – a periodic surge
f/ucfuation a non-periodic surge
spike – a short duration, high amplitude surgesnubber – a surge dampening device which is designed to minimize the effect of pressure spikes andsurges on instruments while allowingchanges in system pressure,and low frequency pulsations to betransmitted to the instrument
rale of pressure change – pressure change per timeinterval
amplitude – the maximum departure of the pressurefrom the ayerage DreSSuTC
3.2 Connections
3.2.1 Type of Connection. Tapered pipe connections for pressure up through 20,000 psi or 160.000kPa are usually’/s -27 NPT,/4 -18 NPT,or ‘/2-14NPT American Standard external or internal taperedpipe threads per ANSI B1.20.1as required.Abovethis pressure,high pressure tubing connections，orequal, should be used. Other appropriarely sized connections, that employ sealing means other than ta-percd thrcads,arc acceptable.
In applications of pipe mounted instruments, whercvibration is extremely severe, consideration should begiven to the possibility of failure of the snubber orassociated piping, caused by the wibrating mass.Alarger connection (eg.,’/ -14 NPT instead of ‘/ 18 NPT) and/or a sfronger material (e.g., stainlesssteel instead of brass) should be considered.
3.3Materials
The internal matcrials must be compatible with theprocess and the external materials must be compatiblewith the environment. The effect of the structural ormechanical loading must also be considered.If ela5-tometric ornonmetallic materials are present,theyshould be selected fo insure compatibility with thcprocess medium,temperature,and pressure.
3.4 Types of Snubbers
3.4.1 Fixed Orifice. This device contains one ormore orifices,and is available in different sizes andconfigurations,The orifice may be in the form of acapillary.The fixed orifice is not adjustable and maybecome plugged in media with suspended solids. Itcan reduce moderate surges in clean systems, See Fig.
3.4.2 Valve.This device consists of an externallyadjustable valve. Closing the valve increases thedampening action. Some valves include long taperedplugs, filters, and/or controlled leak checks. Caution:
ASME B40.5:1995 pdf download
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