4 replies to this topic

[requirement]

Dear all,

I am a new comer to this great forum. I have a question:

Is it necessary to always have a isolate valve in the discharge line of a centrifugal pump while we've already had a check valve?

Other words, when operation or maintenance a check valve can play a role as a isolate valve

I'm looking forward your respond

Thanks and best regards,
Tonny Phuc

[fallah]

Tonny Phuc,

Check valve (non return valve) can not be considered as isolation valve.Therefore in order to pump/check valve maitenance we need to consider isolation valve on the discharge line downstream of the check valve.

Fallah

[tarafdar]

A check valve is not designed for zero passing or leakage.So it can not be used as an isolation valve.Also when you have two pumps ,one is running and other stad-by ,then if the check valve passes(stand-by pump) ,it will rotate the stand-by pump in the reverse direction.You must have an isolation valve to stop this.
Another point is ,when you start a centrifugal pump ,you must start it with discharge valve closed.Otherwise your motor will be overloaded and it will trip due to over current.

Edited by tarafdar, 03 August 2011 - 09:04 AM.

[requirement]

Thanks for your answer

May I add more information about my case? There are 2 pumps, 1 working, 1 stand by. They work with a timer, 2 hours for this pump, then 2 other hours for left.

In this case, the isolate valves are always opened

Best regards,

Tonny Phuc

[tarafdar]

Yes, you have to keep both pumps discharge valve open when they are in "Auto" mode.During start-up or shut-down you do it one by one .This will help you to check pump perfomance and at the same time you can ensure the check valves condition.

Requirement,I like to share your experience of running two pumps with timer.I don't have this experience.Why do you run the pumps with timer?Normally one pump is running and the other starts on "Auto" when running one fails or can not meet the process demand. Stand-by one gets signal from pressure switch fitted on the discharge line