Vertical Pump question
Vertical Pump question
(OP)
Good day,
A question here..I have 5 vertical pumpsets in parallel and they all discharge into a common header. If 3 or more pumps are online, the system functions well, however, if only one pump is in operation, that one pump becomes very noisy as if it's cavitating and its discharge pressure becomes almost 0 psi. However, the sump water level is up fairly high..what could be causing this?? Any ideas?
Thank You.
A question here..I have 5 vertical pumpsets in parallel and they all discharge into a common header. If 3 or more pumps are online, the system functions well, however, if only one pump is in operation, that one pump becomes very noisy as if it's cavitating and its discharge pressure becomes almost 0 psi. However, the sump water level is up fairly high..what could be causing this?? Any ideas?
Thank You.





RE: Vertical Pump question
If you have inverter duty rated motors and MCC + IO space, maybe try VFD(s), otherwise, install some means of discharge throttling. Alternatively, if your process allows it, raise the downstream delivery pressure when you expect to have one pump running.
Regards,
SNORGY.
RE: Vertical Pump question
The simplest solution would be to pinch back on the discharge to limit the flow to a point where you would not require more suction head than you have available.
Johnny Pellin
RE: Vertical Pump question
Ted
RE: Vertical Pump question
RE: Vertical Pump question
RE: Vertical Pump question
I might be inclined to suggest consideration of a bypass globe valve around the discharge block valve, with the globe valve being one size smaller, on the downstream side of the check valve in the discharge line from each pump. When operating a single pump, close the primary block valve and throttle using the bypass globe valve.
Regards,
SNORGY.
RE: Vertical Pump question
Let's assume the pumps are sized correctly as a system. Let's also assume that your system curve is mostly friction (not a high static head rise). What would happen if the flow were reduced significantly.
The system resistance would decrease by the square of the system flow -- that is, the head the pump(s) would see would be reduced.
Let's say one pump is operating. What would it see? It would see the reduced system head. What would it do? It would move way out on the curve. Head would reduce to near zero (your resistance is down from the reduced to 1/9th it's value -- remember resistance goes as the square of the flow).
What happens as it goes out on the curve? You could look at your NPSH requirements, but that may not tell the story. What you would really like to see is the incipient cavitation curve. Such curves (NPSH vs. Flow) for incipient cavitation, are often "U" shaped, where the NPSH head falloff curve is flatter. The bottom of the "U" is normally around the best efficiency point.
What would the pump do, then as it's NPSH requirements suddenly got higher? It would make a lot of noise, head may fall off, and flow drop because the suction was starved.
Could this be your problem? Take a pump curve and estimate a system curve, and find out.
If you wanted to fix this problem, you would need to put flow restriction in the discharge line. This would fool the pump into thinking that the system resistance just got higher. Yes, flow would be reduced, and you'd need to turn on a second or third pump sooner, but you'd be better off.
Run a test. Scrunch down on a system discharge valve. See if the noise goes away.
RE: Vertical Pump question
RE: Vertical Pump question
RE: Vertical Pump question
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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/
RE: Vertical Pump question
Question; are all 5 pumps identical (same make, model, rated conditions, etc)? Ideally you want all pumps operating in parallel to be identical, but with older systems this often isn't the case. If one pump has a higher rated flow/head then the others, consider using that one when the system requires single pump operation.
Did you know that 76.4% of all statistics are made up...
RE: Vertical Pump question