Pump performance curve

[Raziuddin121]

Hey Guys

I want to how can we create pump performance curve according to actual site data?

 

[dbill74]

Pump curve comes from pump manufacturer.
System curve is calculated from a model of the piping.

 

[1gibson]

Measure flow, differential head, and rpm. For constant RPM, plot flow on X axis and head on Y axis. You have to measure pressure on both sides of the pump to get the differential head (you must know the fluid specific gravity.) You could measure power also, and from that data calculate efficiency. Depends on what you need.

 

[Artisi]

Without accurate measuring equipment, properly installed and the test run under rigid test conditions, you will only get an estimate of actual pump performance.
Of course the real question is, what are you trying to establish and why?

Are you trying to compare it to the manufacturers data (performance curve) establish a bench-mark for further information or does it sounds like a good idea to try and do it?

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.)

 

[KMenges]

I agree with the previous posters, accuracy and often times proper calibration of instrumentation are key to obtaining good data. Generally field measurements are only used as en estimate to "check" the pump's performance against curve. If you are trying to validate a published performance curve remember to perform all the necessary corrections before arriving at your final TDH. This includes gauge height differences between suction and discharge pressure gauges and velocity head differences that arise when those gauges are installed in different size pipes. Then you also have to make sure you measure the pumps RPM so you can use the affinity laws to adjust the actual data to the published curve's RPM. Finally you need to adjust for specific gravity (and potentially viscosity if its not water). I recommend gathering all available data you can to double-check your measurements, I.E. gather motor amp draw / voltage as it can be used to back-calculate pump power which can indicate the pump's actual operating point based on the published power curve. FYI I work for an industrial pump OEM and can tell you that most often performance shortfalls on equipment that has been in operation for a while are due to insufficient NPSH/poor suction conditions or worn clearances.

 

[chicopee]

I suppose that you could get an approximate pump performance curve by substracting the results of field test from the calculated the system performance curve.

 

[EnergyProfessional]

chicopee: the calculated system curve is not what is in practice.

 

[chicopee]

EnergyProfessional: I know that, therefore it would be an approximated performance curve.

 

[Artisi]

From many many years of experience, the system curve and the on-site pump performance is never as calculate,expected or required- always either over or under expectations.

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.)

 

[EnergyProfessional]

In addition, you don't get the actual data from the designer (who in most cases is an intern anyway). Assume the designer determines designflow of 36 gpm and 32 ft H2O. And this is based on assumptions, generic K-values, unknown actual valves etc. but the plans will show 40 gpm and 50 ft H2O to include some assumed uncertainty. And the plans are the only information you may have. How you want to have the actual system curve is a mystery to me.

What you could do is:
- measure flow with a magnetic or ultrasound flowmeter
- measure pressure-gain up and downstream of pump. Problem here you want to have some feet of straight pipe, but no strainers etc. included. this may be hard to fin in a field installation.
- change pressure gain and flow by throttling with a valve and plot a curve.

Alternatively, write down the model# of the pump and google for the curve. Keep in min they come with different impellers.