Centrifugal Pump Suction Problem
Centrifugal Pump Suction Problem
(OP)
Hello all,
What types of suction problems could you see in a pump design as follows:
1. Underground sump containing water approx. 13-14 feet down.
2. Pump 4-5 feet away from hole going into sump (operating around 2250 rpm).
3. Motor is 15 hp.
4. NPSH (required)= 9.3 feet.
Attached is a photo of the pump. Let me know if more information is needed. Thanks!
What types of suction problems could you see in a pump design as follows:
1. Underground sump containing water approx. 13-14 feet down.
2. Pump 4-5 feet away from hole going into sump (operating around 2250 rpm).
3. Motor is 15 hp.
4. NPSH (required)= 9.3 feet.
Attached is a photo of the pump. Let me know if more information is needed. Thanks!





RE: Centrifugal Pump Suction Problem
Was that modification discussed with and approved by the pump vendor?
Does the new modified RPM of the pump still allow it to perform properly for the service and installation?
Have you had the Vendor Service Representative out to the plant to evaluate the situation?
RE: Centrifugal Pump Suction Problem
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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: Centrifugal Pump Suction Problem
To give you a definitive answer to your question a pump curve will be needed which give all performance data at 2250rpm operating. This information will allow a closer study of the "suction" lift capabilities and the likelyhood of successful operation under the conditions you have.
Don't forget BigInch's request - this could be very important info.
Appears to be a somewhat neglected and haphazard installation - what is the condition of the pump internals -also an important consideration for a "wet-selfpriming" pump.
RE: Centrifugal Pump Suction Problem
Just question, why you say speed reducer and not speed increaser?
How would you recognize the position of pinion if it is on top or bottom?
Thanks
Rgds
Wimple
RE: Centrifugal Pump Suction Problem
If the piping isn't gas-tight above the water line, you could have trouble, since you have negative guage pressure in the line.
Maybe they slowed it down to get better NPSH performance. Remember, NPSH also follows the affinity laws.
RE: Centrifugal Pump Suction Problem
You wrote:
"Just question, why you say speed reducer and not speed increaser?
How would you recognize the position of pinion if it is on top or bottom?"
Well of course I do not have "X-Ray" vision but I have some smarts.
When you look at the posted picture you see that there is a motor mount that is not now being used. You see that the new motor position is off to the left side of the pump base (viewed from the rear) and at a much lower level relative to the pump center line. Therefore this pump is no-longer a direct drive pump.
So how is this pump connected to the motor?
There are two simple methods to do it and both are consistent with the pictorial evidence.
The two methods are Spur Gear Drive and Sprocket and Chain Drive.
If you look at the picture you see that the "New" coupling cover has very little distance from the motor shaft hole to the edge/bottom indication a small wheel/gear/sprocket. And the cover has a much larger distance from the apparent center of the pump shaft to the edge/top indicating a much larger wheel/gear/sprocket.
The small wheel will turn multiple times for each one turn of the larger wheel.
Thus, in my opinion I think the pump is is running at a much slower speed that when originally manufactured.
RE: Centrifugal Pump Suction Problem
BigInch - The fluid is water and the temperature is 70 degrees F.
RE: Centrifugal Pump Suction Problem
Still need a curve for the operating speed to decide if the pump is capable of the duty you require.
RE: Centrifugal Pump Suction Problem
NPSH should reduce by the square of the speed.
Of course, so will pump todal dynamic head. If that's too low, you don't have an NPSH problem, you have a pump curve/system curve problem.
The original post was about suction performance, though.
RE: Centrifugal Pump Suction Problem
That looks like an old AC pump, what is that, a Trash Hog?
Someone needs to look at the belt drive, and check what the operating speed will be, before basing any decisions on that.
RE: Centrifugal Pump Suction Problem
It's now up to the OP - if he / she can't get us info. how can we help?
RE: Centrifugal Pump Suction Problem
RE: Centrifugal Pump Suction Problem