Centrifugal Pump Has Less Flow Than Design During Commissioning

Hi everyone,

We are having trouble with having less flow for centrifugal pump during commissioning. We are looking for your advises.

we have 8 centrifugal pumps designed at 80m3/h and 57m head, 2940 rpm (Discharge pressure is 5.1barg, and 0.81 barg) for serving chemical fluids.

During commissioning (we use water), Client wants to check flowrate of the pump. We asked a third party to check the flowrate, we used the Prosonic 93T (clamp-on) by Endress+Hauser for measuring at process vertical line at pump discharge. The result showed that flow is 68 m3/h and discharge pressure is 4.9barg. If we refer to the pump curve, this working point is not matching with the curve. (see attached pump curve)

There is no PG installed at pump suction, so we could not know what is pressure at suction. Tank had 1m of liquid, and Low level trip is set at 500mm. Recycle line was fully closed. We also checked the suction strainer and it was clear. We also checked the actual motor speed and it recorded at 2917rpm, slightly lower than setting value of 2940rpm from set value at DCS.

The accuracy of flowmeter could be +-5% (said by vendor), hence, assuming that +5%, we got ~72m3/h which is still less then design flowrate.

When we run the pump at low speed, we got 18m3/h at 1776rpm. If we apply the affinity law for flowrates at low and high speed, they don’t match the rule. (Q1/Q2=N1/N2)

We have checked when the tank has higher liquid level, we have got the same result flowrate. So we eliminated the reason of negative suction pressure.

We checked the pump shutoff pressure when no user and it matched with the pump curve, at 6.7barg

This is my first time working with pump commissioning, I really don’t know if I missed any important point. So if any one of you have a similar issue or commissioning experience, please advise me.

 I attached here the pump curve and other information for your reference.

Thanks in advance for any opinions.

Regards,

Lien

Hi  ,

Make sure your equipment are  well calibrated before use (flow meter ,Pressure gauges, Tachometer ).

I've attached a file to support your work ( field test )

My 2 cents.

Breizh

Edited by breizh, 06 February 2020 - 03:10 AM.

Thanks Breizh. 

Hi  ,

Make sure your equipment are  well calibrated before use (flow meter ,Pressure gauges, Tachometer ).

I've attached a file to support your work ( field test )

 

My 2 cents.

Breizh