Seat Tightness and CDTP differences

[zacharialamsyah]

Can anybody explain to me , what are the differences between Seat Tightness Pressure (per API 527) and CDTP (Cold Differential Test Pressure)? I having difficulties to distinguish clearly between them, because i think this two terms have equal pressure or in other means they were Synonym.. Please someone explain me clearly??

Appreciate for your comment and answer

Thanks and regards
Zachari Alamsyah

 

[Duwe6]

It may be a translation problem. CDTP is the pressure to be used to bench-test a PRV to make that PRV open at the proper pressure while in use. Most commonly for PRV's that are in hot areas. If the spring is several hundreds of degrees hotter than room temp, the ColdDTP will be higher to compensate for the 'limper' hot spring; thus, set [opening] pressure at 100 // CDTP at 103.

For Seat Tightness testing, the PRV is placed underwater and pressurized to 90% of CDTP. The leakage is measured in "Bubbles per Minute", and there are allowable [very small] leakage rates for most PRV's.

 

[SmilerFDL]

In fact API 527 (3rd edition, reaffirmed 07/2007) states "90% of set pressure". I agree with Duwe that 90% of CDTP should be used instead. It seems to me API is not always precise with the use of it's own definitions.

CU, Smiler