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Pump Flow Rate loss over time

Pump Flow Rate loss over time

(OP)
One of our pump stations equipped with two Flyght (6.5)hp pumps has experienced a decreased flow rate over time.
From the pump performance curve, our duty point is 144 gpm @ 57.6 ft of Head
Recent test --> 74 gpm @ 49.7 ft of Head

Our pressures are consistent and we just adjusted the clearances, any ideas why the flow rate has dropped almost 50 percent?

Thank you for your time and energy!

RE: Pump Flow Rate loss over time

If you adjusted the clearances and there is no other reason to suspect excess wear , is it possible that on re installation the electricians have got the rotation in the wrong direction?? Wouldnt be the first time Ive seen it happen.

RE: Pump Flow Rate loss over time

You don't give a lot to go on. Are both pumps operating at the same time? Do each of the pumps provide the same flow rate?

Your pumping system does not operating appear to be operating on the pump curve so that indicates a problem. You need to inspect the pumping system and get some further informatin.

The pump may be clogged?

The forcemain may be fouled?

What is the elevation of the water in the lift station?

What is the velocity in the force main?

Is the flow meter accurate?

etc

RE: Pump Flow Rate loss over time

Are the pump/s worn - this could account for the drop in performance. Don't rely of hearsay that everything is OK - go and check them yourself.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Pump Flow Rate loss over time

Check the pump suction. It very well may be clogged with a rag or debris. If it was a dry pit pump you probably could hear something is wrong.

One way to check this out is to reproduce the pump curve:

1. The shut in head matches the shut in head on the curve
2. The further you produce points to the right of the shut in head, the further the droop away from the pump curve....for sure you have debris in the pump suction

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