Speaking of PRV testing, everyone knows (1) Pop Test or Set Pressure Test. It is a test whether PRV can open at Inlet Pressure as set and or (2) Seat Tightness Test, which we call Leak Test, which is the test of leakage between Disc and Seat of PRV after Pop Test.
But for Closed Bonnet PRV in a closed system and does not require Fluid is leaking to the outside (Discharge to Closed System) must be made Backpressure Test on Requirement of ASME BPVC Section VIII, Div.1
The Backpressure Test is a compressed air or gas at a pressure of at least 2 bars. Go from the outlet side of the PRV to see if the Body, Bonet, Bellow, including Gasketed Joint and Connection are leak or not. Which we will use soapy water to help find the leak.
To do Backpressure Test can also detect leaks of Bellow’s principle is that if a leakthrough Bellow we can Detect the hole Vent ‘s Bonnet.
What if we do not carry out Backpressure Test?
The leak of Bellow would make it unable to compensate Backpressure as the result PRV can not open the vent pressure to meet Set Pressure pre-set and leakage of Fluid on the outside could harm the environment or device.