13 replies to this topic

[Pronab]

When pump is stand-by, if suction strainer is already dirty, should Pressure Differential Gauge(PDG) will show reading? I found one of our stand-by pump suction strainer PDG showing 3 bar, suspecting PDG may be faulty reading. While instrument technician checked PDG found it is OK. Should I clean pump suction strainer??

 

[fallah]

pronab,

 

Lack of a simplified sketch....

 

Anyway, appears suction pressure to be around 3 barg and the stand by pump would be started automatically i.e. with open suction and discharge isolation valves. If so, seems suction strainer needs to be cleaned...

[Zauberberg]

No flow, no pressure drop. The DP gauge should read zero at no flow condition.

 

If there is an isolation valve between the two instrument tapping points, sometimes leaving it in a closed position leaves a possibility for the fluid to "escape" towards the pump, thus creating pressure differential.

[Pronab]

Pump suction & discharge kept open to observe, found same result, differential pressure was 3 bar. As per Instrument, PDG reading is correct. Does it mean pump suction strainer is chocked?? It is a centrifugal pump with suction and discharge isolation valve and a non-return valve in discharge line.

[fallah]

pronab,

 

You fail to specify if stand by pump would be started automatically i.e. suction and discharge isolation valves are permanently open...

[Pronab]

Fallah: Stand-by pump start in Auto, suction/discharge are permanently open.

Edited by pronab, 03 May 2015 - 11:53 AM.

[fallah]

Stand-by pump start in Auto, suction/discharge are permanently open.

 

Then, as i mentioned suction strainer needs to be cleaned...

[Pronab]

Pump suction strainer open and found it is not dirty, it is clean. In fact it was suction strainer differential gauge(PDG) showing faulty which Instrument technician fail to calibrate correctly.

[fallah]

Pump suction strainer open and found it is not dirty, it is clean. In fact it was suction strainer differential gauge(PDG) showing faulty which Instrument technician fail to calibrate correctly.

 

pronab,

 

In your first post you mentioned "...instrument technician checked PDG found it is OK..." while now you say PDG showing faulty due to lack of proper checking by them...
 

[Zauberberg]

Pronab,

 

I have written in my first post that having pressure drop at zero flow is not possible. If you read that post, you would have saved yourself the trouble of checking the strainer.

[fallah]

 

I have written in my first post that having pressure drop at zero flow is not possible.

 

But as i mentioned it could be possible having differential pressure across the strainer at zero flow, where in auto start stand by pump suction strainer is blocked due to dirty fluid and upstream of strainer is subject to suction pressure while the trapped fluid between strainer and discharge check valve isn't subject to any pressure source...
 

[Pronab]

Yes I waste my time including maintenance efforts. It was instrument problem came to our shoulder now!!

Thanks a lot for your time and patients.

[siddiquiee]

Yes I waste my time including maintenance efforts. It was instrument problem came to our shoulder now!!

Thanks a lot for your time and patients.

For any maintenance  due to any reason need to check first instrumentation like  zero of PDG by draining the liquid from manifold

[Pronab]

Siddquiee: I agree with you and that job as you mentioned, done by instrument. Before going to next step we approach to Instrument several times for their confirmation and according to instrument PDG was giving correct(?) reading.

Thank you for your time.