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Centrifugal pump curve falls short of factory test 3

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sboswell

Civil/Environmental
Jul 8, 2010
13
against the factory testing that is..

This is a drop of a substantial amount. close to 20 gpm difference at 30ft of discharge head which is the lowest our piping system will go.

pump shutoff measured here and at the factory is 47 ft.
NPSH is 2ft, 2.0hp, 1750rpm, pump is a 6.125" impeller, 1" discharge dia, 1.5" suction dia. factory BEP Flow is 55 gpm. our field tested rpms during operation have all been better than 1750rpm. we've changed out the suction piping to a few different configurations tank + valve to a stand pipe and 3" continuous suction piping leading up to the pump. flowrates and pressures have been double and triple checked with calibrated equipment onsite and several different gauges and styles of flowmeters.

I though a pump curve can only change due to loss of rpm or a suction side starvation. We've also vibration tested the pump and checked its impeller clearances. Any help is greatly appreciated.

Sam Boswell
 
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To replicate carefully controlled and documented factory performance testing under installed site conditions verges on the near impossible -- unless of course all instrumentation is installed strictly inaccordance with the testing code, on correctly installed pipework with steady flow conditions of air free water at standard temperature etc etc - any deviation from these conditions means that the results of "site-testing" is suspect from the onset regardless of any fudge factors introduced to correct variances of the testing conditions.

One reason why it is unusual for a pump company to guarantee pump hydraulic performance based on site testing.
 
I think its definitely a velocity phenomenon. Vortexing from the multiple plane turns and the reducer, quite possible. There's a lot of acceleration going on in that reducer too.

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