Power in Parallel Pumping
Power in Parallel Pumping
(OP)
Good day All,
A question here..I have 6 vertical pumps in parallel. Now, all 6 were fitted with slightly larger impellers. With this upgrade, their BHP's have gone up to around 600 horsepower. From the attached sketch you can see the arrangement. All 6 discharge into a large 42" header which splits into 2. The header then goes to a bank of filters entering on either side. All the pumps, with the exception of one, are operating at around 595 horsepower with a discharge pressure of 82 psi. Pump C, from the sketch, is operating at 615 horsepower with a discharge pressure of 86 psi. All 6 pumps were sent at the same shop, and all 6 had more or less the same repair work done to it and fitted with the same sized impellers and suction casings. Can anyone explain why this pump is drawing more power? I included the sketch because I'm not sure if its position on the header has anything to do with it??
Thanks!
A question here..I have 6 vertical pumps in parallel. Now, all 6 were fitted with slightly larger impellers. With this upgrade, their BHP's have gone up to around 600 horsepower. From the attached sketch you can see the arrangement. All 6 discharge into a large 42" header which splits into 2. The header then goes to a bank of filters entering on either side. All the pumps, with the exception of one, are operating at around 595 horsepower with a discharge pressure of 82 psi. Pump C, from the sketch, is operating at 615 horsepower with a discharge pressure of 86 psi. All 6 pumps were sent at the same shop, and all 6 had more or less the same repair work done to it and fitted with the same sized impellers and suction casings. Can anyone explain why this pump is drawing more power? I included the sketch because I'm not sure if its position on the header has anything to do with it??
Thanks!





RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
Another possibility. Is the Tee at C too close to the end of the header? It is discharging into a dead end region, so it may be experiencing some additional head due to turbulence in the header. A Tee is not as streamlined as an ell fitting, so extra pressure may be needed there. How close is the end of header at pump C when compared to the distance to the end of the header at pump F?
Other than that, you've only have 1 of 6 pumps with less than a 5% difference, which is well within typical variance. Keep your eye on it, and if it doesn't get worse, don't worry too much for now.
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"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Power in Parallel Pumping
I would really appreciate any further help!!!!
Thanks
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
Sorry no text on the subject.
**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping
Also, if pump C is operating at a higher discharge pressure, won't it mean that the pump will operate to the left on its curve therefore reducing the power?? This is what confuses me.
And well here's the other part..The pump manufacturer themselves made these impellers for us, however, they botched up their calculations. They were supposed to design an impeller to allow an increase of flow from 8000 usgpm to 10,000 usgpm at a power of 595 hp. However, when it was all said and done, the actual performance is 9,600 usgpm @ 600 horse. The constraint here is that my motors are rated at 600 horse! This is why I do not want to exceed that 600 horsepower limit.
RE: Power in Parallel Pumping
The confusion regarding the increased power for increased head is a function of axial flow impellers, unlike low specific speed pumps (centrifugal) where power decreases as head increases.
As we know know that these are axial impellers it seems that it could well be a function of header hydraulic / pump outlet problem which you are stuck with.
The cure for pump C looks to be a reduced diameter impeller and a new impeller wear ring to suit the new diameter. A small diameter change will hardly be noticeable in terms of flow but give a bigger change in power input, remember power chages at the cube of the diameter change.
RE: Power in Parallel Pumping
BigInch also had a good point in which if it says within 5% deviation from the other points, why worry? Just keep an eye on it.
"Scientists dream about doing great things. Engineers do them." -James Michener
RE: Power in Parallel Pumping
the horse power, might it be derived from amps measurement?
if so, current might have gone up, together with cos phi.
so actual hp or kw might have gone down
RE: Power in Parallel Pumping
On axial flow impellers, increase head with reduced flow means increased power input.
RE: Power in Parallel Pumping
I was just quoting the OP, commenting his question
RE: Power in Parallel Pumping
And the thought of a larger impeller crossed my mind..but I'd like to think the manufacturer made all 6 impellers exactly the same.... but then again, they did botch up their calculations so anything's possible.
RE: Power in Parallel Pumping
Do you have any record of pump powers before re-impllering?
Reza
RE: Power in Parallel Pumping
Bottom left (sorry not all that clear) shows impeller shape as Specific Speed increases, axial flow impellers are about 9000+, bottom right indicates typical power curves for various Specific Speeds, curve No5 is typical axial flow and shows increasing power as flow reduces.
RE: Power in Parallel Pumping
Can you extend your original rough P&ID to include piping upstream of the said bank of pumps?
"Scientists dream about doing great things. Engineers do them." -James Michener
RE: Power in Parallel Pumping
RE: Power in Parallel Pumping