Usage of Non Return Valves

Only when the outcome of the HazOp Study deems to necessary.

They would ordinarily be after the pumps, anyway.

thanks for replying my question ,but my point of view is why you need a non return valve if your pump is positive displacement pump , which all of us know that it is a type of pumps normally committed to a specific and fixed volume it discharge in each cycle , the scenario am imagining that if the pump stops , even without an NRV the flow will not be able to go back to the pump , so why i should i add a valve in such a case !

right ?!

please correct me if am wrong and thanks for sharing the info..

If the pump discharge is at significant pressure, and then the pump stops, the pressure can drive the pump backwards. This is true for positive displacement pumps as well as dynamic pumps.

so the conclusion that you mean to say that even if the pump is positive displacement pump you still need to add an NRV on it`s discharge ..right ?

If it is inappropriate for the pump to run backwards, and only local conditions can dictate it, then fit a non-return valve. There is no general answer.

There's more than one type of positive displacement pump. A piston type usually has internal spring-loaded inlet and discharge valves so an external valve may be unnecessary. A helical-rotor pump has no built-in valves.

Also it depends on the arrangement. There's a stronger case for needing one if 2 or more pumps are feeding a common header.