Location PSV upstream or downtream a check valve blocked in closed position ?

[Matchess]

Good morning

I am designing a lube oil system for a turbo expander
This turbo expander is supplied with two oil pumps (1 for normal operation + 1 for back up)

A check valve is placed dicharge line of each pump

and I am asking if two PSV placed upstream of eash check valve are required to avoid overpressure, or if one PSV placed downtream (T connection)of the (*2) check valves is sufficient.

In other words, shall we considered check valve could be blocked in closed position or not.(API requirement ?)

Are there any standard dealing this problem ?

Thanks in advance for you reply

Best regards

Matchess

 

[LittleInch]

The standard will be your piping design standard - ASME B31.3 at a guess. From the info you have given a single PSV downstream of the check valves should be sufficient, but does depend on the lcation of any isoaltion valves (manual or actuated). In my experience check valves are assumed for these purposes to work efficiently in both directions, i.e. fluid at a higher pressure will go forward through the valve, but not in the reverse (check) direction.

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Also: There's usually a good reason why everyone does it that way