9 replies to this topic

[simadri]

I have a query. Pressure gauge shall be provided at centrifugal pump discharge before check valve or after check valve. Hope, it will be a good brain storming session.

[fallah]

simadri,

After discharge nozzle and before check valve.

Fallah

[simadri]

Fallah

I will be happy if you can tell me the reason for that. Somebody told me that check valve shall be as close as possible to pump discharge nozzle.

[fallah]

simadri,

Pressure gauge shall be provided at centrifugal pump discharge before check valve and as close to pump discharge nozzle as possible because it is installed there to show the pump discharge pressure and if to be installed after check valve wouldn't show exact pump discharge pressure due to differential pressure across the valve.

Fallah

[simadri]

Fallah

But differential pressure across check valve comparative to pump discharge pressure is very small. Then what is the big deal if I will put the pressure gauge after check valve?

I have also another question. If I have a no flow switch at pump discharge, then where should be its location and why?

[kkala]

I see in a local PID that PI is placed between centrifugal pump and check valve. I believe that this covers the case of check valve failure - stuck closed. By observing the PI, you can conclude that check valve has problem, not the pump. Or that the pump has problem, if PI shows lower than usual operating pressure.
It is noted that min flow line is also connected between pump and check valve. So if check valve stucks closed, the pump will be protected by circulation through this line.
See also http://www.cheresour...-valve-failure/ '> http://www.cheresour...-valve-failure/ .
Is there a min flow line? If so, I would place the no flow switch downstream check valve, net flow is of interest. If no, I would place it upstream check valve, thinking of better protection against water hammer (during startup or sudden stop of the pump).

[fallah]

what is the big deal if I will put the pressure gauge after check valve?

simadri,

Then:

1- You cannot verify pump depressuring for maintenance
2- You cannot check actual pump discharge pressure for performance evaluation
3- You cannot meet some codes (e.g. ANSI K61.1) requirement to install pressure gauge immediately after the pump discharge nozzle
4- You cannot make true reading of discharge pressure of the pump
5- Looking at maintenance point of view, you cannot evaluate check valve leakage when the pump is tripped and the discharge line isn't blown down

Fallah

Edited by fallah, 22 April 2012 - 03:23 AM.

[simadri]

Kkala & Fallah

Thank you for the important information shared by you.

Fallah

Can you please tell me how to do and verify pump depressuring for maintenance in detail?

[fallah]

Fallah
Can you please tell me how to do and verify pump depressuring for maintenance in detail?

simadri,

It means if you would isolate a pump by closing suction/discharge isolation valves during maintenance and decide to depressure the pump (e.g.by opening the pump vent), you would realize the time mentioned pump is depressured by reading the PG, only when the pressure gauge has already been installed between pump and the check valve.

Fallah

[simadri]

FallahThank you very much