Pumps in Parallel
Pumps in Parallel
(OP)
Good day,
My Boss threw an idea at me which while sounds correct in theory, I'm not sure how accurate it is practically. We have 6 vertical pumps in parallel and there's a discharge gauge on each. We have no individual flowmeters, just a total flow of all 6 pumps from the header. My boss was suggesting to check the power required by the pump and use this value on the power curve to obtain a flow value and then plot this on the performance curve with the pressure value from the gauge. Is using the power to obtain a flow value accurate?
Thanks
My Boss threw an idea at me which while sounds correct in theory, I'm not sure how accurate it is practically. We have 6 vertical pumps in parallel and there's a discharge gauge on each. We have no individual flowmeters, just a total flow of all 6 pumps from the header. My boss was suggesting to check the power required by the pump and use this value on the power curve to obtain a flow value and then plot this on the performance curve with the pressure value from the gauge. Is using the power to obtain a flow value accurate?
Thanks





RE: Pumps in Parallel
Johnny Pellin
RE: Pumps in Parallel
You've already got a valid answer by JJPellin, anyway I suggest you to take a look at this thread
http://www
RE: Pumps in Parallel
Hopefully you have got a performance test curve for each pump. if so then you are better getting the head generated from each pump using a pressure gauge at the pump discharge, and having a pressure gauge at the pump suction.
take the suction pressure from the discharge pressure and you have the pump generated head. plot this onto the pump perf curve and this should give you the flow.
this is better than trying to use the power to get the flow.
RE: Pumps in Parallel
Johnny Pellin
RE: Pumps in Parallel
I have used portable Polysonics Doppler meters before to get flow measurements (circa 1990s) when I otherwise had no device to rely on. I rented them typically for about $100.00 per day. There is probably even better technology today.
Regards,
SNORGY.
RE: Pumps in Parallel
Whichever is shut (or only partially open) is attached to a failing/failed pump.
RE: Pumps in Parallel
**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Pumps in Parallel
I once had to use the technique you want to use in a power station to corroborate the flow data I was getting from the condenser DP and from the TDH measurements across the pumps and fortunately they knew their station PF, so the technique worked and the flow measurements checked out.
rmw
RE: Pumps in Parallel
Johnny Pellin
RE: Pumps in Parallel
Another question on this topic, what's the theory behind lowering of the water level in the basin, and the apparent increase in the horsepower required by the pump. When the level is raised, the power required is less. Why is that?
RE: Pumps in Parallel
The Brake Horse Power, that is the work done by the pump is
BHP = (Ht * Q * SG)/(3960 * Eff)
Where:
Q = flow rate
SG = liquid specific gravity
Eff = pump efficiency
Increasing the suction head Hs (reservoir above centerline of the impeller) the total differential head Ht decreases:
Ht = Hd – Hs (being Hd the total discharge head)
So decreasing Ht, BHP decreases as well.
RE: Pumps in Parallel
RE: Pumps in Parallel
RE: Pumps in Parallel
If a very mixed or axial flow impeller, power will probably increase as the sump level reduces and head increase due to a rising power curve as head reduces for high specific speed pumps.
To say that power will increase for radial flow impellers as head increases assumes that flow remains the same which is unlikely.
RE: Pumps in Parallel
Johnny Pellin
RE: Pumps in Parallel
In your statement you mentioned you don't have individual flow meters... do you have one flow meter on the common header, or a better way to measure total flow?
If all the pumps are identical, and all are reading approx. the same discharge pressures, individual flow of each pump should be directly proportional (ie. 4 pumps in parallel, indiv. flow is 1/4 total flow.)
Did you know that 76.4% of all statistics are made up...
RE: Pumps in Parallel
If all pumps are connected to the same header and operating then all pumps will have the same identical discharge pressure irrespective of individual flowrates.
RE: Pumps in Parallel
RE: Pumps in Parallel
Start a new thread for your question there is no point to tagging it onto this thread.
RE: Pumps in Parallel
And if all pumps are identical and have a good head rise to shut off, then they'd be approx the same flows for that given pressure.
Did you know that 76.4% of all statistics are made up...
RE: Pumps in Parallel
have a good look at the shape of the curves and you should be able to tell if measuring the power can help you identify the weakest pump. This is usually difficult and can be inaccurate since pumps discharging on a common header influence each others operating point.
the most accurate method would be to use an ultrasonic flow meter; provided you have a good straight run of piping on the discharge of each pump.