Unless you test on the actual system being protected, you will not be able to 100% recreate the relieving scenario - you would not want to create a fire case or a blocked outlet etc. etc., would you?

Even laboratory flow/coefficient testing for PRV certification (National Board) is using just 'simple' parameters for testing.

This is why the usual only option, is the workshop test bench test. Here you use air or nitrogen for PRV's on compressible fluid applications, and water as the test medium for liquid PRV use. For multi phase flow, take the manufacturers recommendation. Steam safety valves should be set on steam where possible. For workshop test bench testing you also use the CDTP - Cold Differential Test Pressure for the effects of static back pressure (non balanced PRV's) and operating temperature (manufacturers recommendation for testing at ambient conditions).

The above is generally in most, if not all recognised standards such as API-527.

Other testing methods such as in-situ testing, are done on line, but this verifies the set point but not the true relieving condition that may occur.


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

thanks for your feedback. i will explain you our concern..
Now Process Engineer is filling the PSV Authorization form and test media need to be filled in the form. Based on the test media mentioned on this form, work shop personnel will decide, psv need to be tested in which test stand(Air/Liquid).

PSV is installed on the Drum and service is liquid. During relieving condition, it will be in Gas form. So, Process engineer is confused, psv test media is Gas or Liquid. we need to consider the normal operating condition or relieving condition..

In the case you mention, you need to test with the medium that corresponds to the most probable relieving condition. The relieving condition is when the PRV is expected to open, so it makes sense to test for a similar condition.


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

Thanks for your feedback..