Centrifugal Pump Discharge Lines

MOV ?

Gopu,

You should not use abbreviations unless you fully define them first.

- MOV = "Motor Operated Valve" - This can be any type of shut-off valve consistent with the requirements of the specific piping line class specification which is fitted with an electric motor , an air cylinder operator or other type of assistant to aid in the operation of the opening or closing of the valve. Motor operators can be mounted on Gate valves, Plug valves, Ball valves, Butterfly valves, etc.

- NRV = "Non Return Valve" -This in nothing more than a simple Check valve

There is no problem fitting the pump discharge valve with a Motor operator however the sequence of valves in the direction of flow for any pump discharge SHOULD be pump discharge then the check valve then the block valve.

So the answer to your specific question "MOV is installed before the NRV" is wrong.

O.K. His question is what is the problem if MOV is installed before NRV?

A pump usually has a manual isolating valve on the delivery. Not essential, but enables pump to be removed for maintenance without draining tanks/pipework. Discharge NRV also often provided but again not essential, depends on the system e.g. it's not needed on a central heating recirculation pump, because there is no tendecy to backflow when the pump stops.

If both are fitted, it's usual to fit the NRV upstream of the isolating valve so the iso valve can be closed and the NRV removed for maintenance, on basis that the NRV is likely to fail before the iso. If there is a MOV as well as a manual iso valve the iso should be downstream of both, for same reason.

It doesn't make much difference hydraulically which way round the NRV and MOV are, so if there is no manual iso valve it depends whether you think the NRV or MOV is likely to fail first, and if it's the MOV, whether you're happy working on it and relying on the NRV to seal well enough - hazardous fluid, temperature etc.

Cheers........Codey

Answer - if the NRV fails or leaks or needs attention, the MOV cannot be used to isolate it.

Hello PW - why do you say that?

OP hasn't given any information on what the MOV is doing or valve size. It might be just used for isolation on a big line, and the valve is motorised only because operating it manually would be too much like work.

Cheers...........Codey

Excuse me guys.. He is asking about having valve ahead of a NRV in the discharge line of a "centrifugal pump" ! I believe , a centrifugal pump should always be started with its discharge closed and an MOV will do good if installed before the NRV.