Pump Curve

[impeller1]

Good day,

I am trying to approximate the performance of a pump onsite. When plotting the point on the curve, the Total head the pump is operating at does not correspond to the flow its delivering. The flow its ACTUALLY delivering is around 5,100 gpm, while the flow it's SUPPOSED to deliver based on the curve is around 3500 gpm. The way the system is designed, the pump doesnt have a choice but to pump this flow of 5100 gpm. I checked the hydraulic power curve and it matches the power used by the motor (taking efficiencies into account)to deliver the flow of 5100. Is it possible for a pump to operate like this??

 

[JJPellin]

The short answer is no. It is more likely that there is something wrong with the data you are using to calculate the pump performance. We can be more help if you give us the details. What are you using for suction pressure, discharge pressure, specific gravity, etc.? How and where are you measuring the pressures and flows? Have you verified rotational speed? Are you certain you have a curve for the installed impeller diameter and actual operating speed? Are you using a test curve for the exact pump in question or a generic "book" curve for that model and size? A sketch of the system with measurement points and controls would be helpful. A description of the pump configuration would also help us provide more useful comments.

A pump curve is defined as all of the operating points that a particular pump is capable of running at. If you are plotting the pump performance 46% greater in flow than shown on the curve, then you have bad data or the wrong curve for that pump.


Johnny Pellin

 

[BigInch]

Maybe you're modeling the pump properly, but don't have the correct system curve. Check the discharge piping, or discharge control valve configuration, or backpressure setting at the end of the piping.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JohnGP]

Ok, if I had to guess, I would say that pump Suction Head has not been deducted from pump Discharge Head to obtain the Total (Dynamic) Head point to plot on the pump performance curve.

 

[Artisi]

Sounds like a typical hit and miss site test, we think it is 5100 GPM but it should be 3500 etc. Testing pump performance under ideal conditions with an accurate test facility is difficult enough and to undetake and obtain accurate insitu field test needs accurate and co-ordinated testing at least somewhere near to the accuracy of a test facilty. As pointed out by Johnny P you need to measure all data under steady flow conditions and confirm the data you are using as the reference.

 

[JohnGP]

I think I misinterpreted the situation with my earlier response. Assuming this is a centrifugal pump, it seems like the pump is operating at a lower TDH than dictated by design. A first step might be to check the system resistance calculations against what is actually installed, i.e. redo the system curve.

 

[Artisi]

Sure it could be operating a lower head - but accurate figures are needed to confirm where the pump is running, at the moment it all seems like guess work.