2 replies to this topic

[Raj Mehta]

What exactly is the difference between Safety valve, relief valve and safety relief valve. ?

I have referred API 520, but I wish to seek more information on the difference between them, if any ? Under which conditions you use either of the valve (applicability) and constraints.

 

If you have any reference, kindly share them .

 

Thanking you in advance. 

 

Regards,

Raj Mehta

[Justin P]

Raj,

 

Although used interchangeably all the time (most people think of RV, PSV, PRV all as the same thing), the terms can be associated as follows:

Safety: Vapor
Relief: Liquid
Safety Relief: Both

 

API Std. 520 Part I discusses the difference between valves designed for liquid relief and those for vapor relief (it has a lot to do with valve seat design). API Std. 520 Part I goes on to explain the constraints of using vapor-trim valves in lquid service (impact on capacity, etc.). It's a bit of a sordid subject and philosphies for when to use what differ among valve vendors, engineering firms, and operators.

 

Typically, you trim your valve based on the controlling scenario. Blocked pump discharge? Use a liquid relief valve. Blocked outlet on a compressor? Use a vapor relief valve. Mutliple potential relief phases/scenarios? Consider a dual-certified conventional valve or even a pilot-operated valve.

 

Justin

[Raj Mehta]

Mr. Justin, Thank you very much for your inputs.