Pipe discharge configuration

[essenwood]

Hi guys,
I always see that the drain valve on a pump discharge is between the NRV/check valve and the downstream block valve (NRV, drain valve, block valve). Is there a particular reason why the arrangement is like that? I.e. can I have instead the drain valve up stream of the NRV? (drain valve, NRV, block valve).

Thanks in advance.

 

[pennpiper]

There would be product trapped at operating pressure between the check valve (NRV) and the block valve.
Think about it.

 

[itdepends]

Q If you've shut a pump down- how do you drain down the piping downstream of the check valve?

A The first thing you put downstream of a check valve is a drain (unless the pipe slopes down- that minimises the dead section you can't drain otherwise.

 

[roydm]

The drain location is not always in the same place, it could also be in the pump casing. It depends on a lot of different factors for example Hazardous nature of chemical, pipe orientation etc. The drain location is usually discussed at great length when a HAZOP study takes place.
Roy

 

[essenwood]

Dear all,
Thanks for your replies.
I was thinking that the dead end section can be drained through the pump casing by way of a bypass line around the NRV.