5 replies to this topic

[A mukherjee]

In any centrifugal/reciprocating pump is it necessary to put the NRV ahead of isolation valve at the pump discharge?Also is there any requirement of maintaining min.distance between pump discharge flange & NRV?
Waiting for your answer.
Regards,
Arpan

[USR]

Dear Arpan,
From what i have obseved in my one month exposure to a process plant,i have not seen any NRV provided separately in the discharge line of a reciprocating pump.The reciprocating pump has its own suction and discharge check valves.What you would find in the discharge line of the reciprocating type pump is a pulsation dampener and a PSV.
But i have seen NRVs on the discharge line of centrifugal pumps.This i suppose is provided to prevent back flow of the fluid from the high pressure discharge side to the low pressure suction side in case of any mishap such as say the pumps motor trip.Hope this helps.waiting for experienced comments.

Edited by USR, 19 November 2010 - 02:50 PM.

[Zauberberg]

Check valve is mandatory regardless of the type of pump, whether it is centrifugal or reciprocating. The main reasons are:

- Prevent reversed flow in case of parallel pumps (running/standby);
- Prevent reversed flow from the pressurized section downstream of the pump(s).

The distance in between isolation valve and check valve should be kept sufficient to install a small drain connection, so as to ensure safe removal of the check valve when maintenance is required.

[A mukherjee]

I think i've been not able to express my querie.
Providing NRV at the pump discharge is mandatory.
I want to know is it necessary to provide isolation valve after the NRV at the pump discharge or vice-versa?
Also do we need to maintain min.distance between pump discharge FLANGE & NRV?
Thnx in advance.

[Zauberberg]

Mukherjee,

Grab a sample of any pump P&ID and you will see the following arrangement: NRV followed by isolation valve. Isolation valve (and the drain/vent connection in between) is required for maintenance activities on the NRV, and on the pump as well. Otherwise it wouldn't be possible to isolate and access these equipment in a safe manner.

The distance in between is as I wrote in my previous post: sufficiently long enough to provide space for the drain/vent connection in between the valves. Depending on the piping/valve size, this can be as low as e.g. 100mm or as high as 1,000mm.

[asade abiodun]

The function of a block valve at the discharge outlet of a pump cannot be ignored. Especially when you have more than one pumps in operation. It helps you to isolate the pump for maintenance and other activities that needs to be carried out around the pump area without affecting other pumps operation.

regarding the minimum distance, i concur with what Zauberberg stated earlier. This should be discussed with the piping engineer for futher clarification on fittings arrangement.

Regards.