Testing a pump dead-headed
Testing a pump dead-headed
(OP)
Good day Folks,
Im sorry if this is a dumb question, but I have 6 vertical pumps. I'd like to test them to determine where they're operating on their performance curves. However, I do not have the system curves and I'd like to test the pump alone minus the system. These pumps are VFD's so I can vary the speed to vary my flows and heads. They're high head, rated - 388 feet @ 4422gpm. Is it acceptable to close the discharge valve on the pump and quickly take the pump through about 5 different speeds to obtain flow and head values? I know the water would recirculate in the pump and may increase vibration and temperature on the bearings and pump itself, but if it's done for only a short time just for me to get my readings, is it plausible? And would I then be able to ignore them system curve as the discharge valve is several feet from the pump discharge.
Thanks
Im sorry if this is a dumb question, but I have 6 vertical pumps. I'd like to test them to determine where they're operating on their performance curves. However, I do not have the system curves and I'd like to test the pump alone minus the system. These pumps are VFD's so I can vary the speed to vary my flows and heads. They're high head, rated - 388 feet @ 4422gpm. Is it acceptable to close the discharge valve on the pump and quickly take the pump through about 5 different speeds to obtain flow and head values? I know the water would recirculate in the pump and may increase vibration and temperature on the bearings and pump itself, but if it's done for only a short time just for me to get my readings, is it plausible? And would I then be able to ignore them system curve as the discharge valve is several feet from the pump discharge.
Thanks





RE: Testing a pump dead-headed
You do have the pump curves, right? So if you know the pressure difference and the RPM, you can estimate the flow, which lies on the system curve.
Change the RPM, get another pressure difference, estimate the flow using the pump curves, and you can map some of the sytem curve. Or just log the DP and RPM as the pumps do their thing.
Or extrapolate from the one point. If nothing else changes, the entire system curve should follow a square law curve, of the form Q{gpm}=Cv*sqrt(deltaP{psid})
Mike Halloran
Pembroke Pines, FL, USA
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Testing a pump dead-headed
I agree with the other replies above. If you can run the pump under normal flow conditions at a couple of different points, you have three variables that you can measure to determine where you are at on the curve: Discharge pressure, motor amps and flow rate. Depending on the piping configuration, the clamp-on flow meter may be the least accurate of the three. But, between discharge pressure and amps, you should be able to confirm or deny the flow measurement result. We do this with our largest cooling tower pumps since it is impossible for us to get any flow measurement for an individual pump.
Johnny Pellin
RE: Testing a pump dead-headed
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
RE: Testing a pump dead-headed
**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Testing a pump dead-headed
On the mfg test bed, radial flow impellers in vertical pumps are taken back to shut off almost all of the time.
Axial flow impellers in vertical pumps, not so much as the HP rise to shut off and down thrust generated are often too high for the motor.
I've done many field tests as well and agree, pumps should not be intentionally taken back to shut off when installed. MCSF is close enough.
Did you know that 76.4% of all statistics are made up...