Reduced pump flow

[Edadunn]

I have an installed pump that is producing just over 50% of its design capacity flow. The pump was tested on a controlled test floor and verified to meet the performance it was designed for, i.e. 100%. Based on those findings, I am concerned that there is some line restriction at the installation that is unaccounted for.

The only thing that has been reported to me is that the discharge pipe has a high spot approximately 200 ft. from its open atmospheric discharge. The high point is not enough to increase the static head to the reduced flow reported above, but it may be able to trap an air bubble at this point. Does anyone know of a calculation to determine if the water should be able to remove, i.e. push, this air bubble to the discharge point, or is an air relief valve required regardless of the location of the high point?

 

[rzrbk]

If the flow is restricted, it will show up in the pressure rise across the pump. The difference in discharge and suction pressure should be measured in order to verify if the pump is running back on its curve or below its curve.

If the pump is running on its curve, the measurements should also tell you if the restriction is on the suction or discharge side.

If the pump is running below its curve, things to check for are cavitation and correct rotation.

 

[BigInch]

Actually it sounds like it might be a power problem or perhaps running in reverse???

You can have a look for Lockhart-Martinelli 2 phase flow correlations. You can find an example of this method here,

http://www.tijsat.tu.ac.th/issues/1998/no2/1998_V3_No2_5.PDF

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[LHA]

Agree w/ Biginch on this one, for both culprits.

Check the line amps and volts on each leg (if multi-phase) against the motor plate. If amp draw is low, check connections and transformer sizing, and power out of xformer.

Also, if(if multi-phase), check lines in are aligned as the logic describes. If not, could be running in reverse.

Engineering is the practice of the art of science - Steve

 

[FACS]

I would think that an air bubble on the discharge would not cause a problem.

I agree with rzrbk on this one; Check the pressures at the input and output of the pump. Make sure the proper head if feeding the pump, and then make sure there is not a build up of pressure from downstream restriction.

The pump checked out during testing, make sure it was wired correctly. ie voltage taps.

Charlie

http://www.facsco.com

 

[FACS]

Steve,
"Engineering is the practice of the art of science - Steve"

OK, I'm going to be a smarty on this quote of yours, but it's just for fun.

1) art has nothing to do with science, art is subjective and artists are wierd.

2) We do not "practice" anything, we are good at what we do.

Sorry, I had to say it.

"Engineering is the manipulation of natural resources by man, to create a world that nature can not."-- Charlie


Charlie

http://www.facsco.com

 

[LHA]

Charlie-my-smarty-pants friend:

Art and science are complimentary, not identical. Art is subjective, science is objective. Mastering either without the other makes one a poor engineer, IMHO. It leads to rote, cookie-cutter design and spec's that are only loosely relavant to what is actually being built. Some artist are weird, as are some scientists. I consider myself both, and my wife considers me weird, so I agree with that part.

Quoting and citing the laws of PA, USA (where I PRACTICE):
To be eligible for PE licensure, which I have, so I am required to PRACTICE: "Work experience...shall be of a grade and character to qualify the applicant to assume responsible charge of the work involved in the PRACTICE of engineering."

http://www.pacode.com/secure/data/049/chapter37/s37.31.html

Your signature is true and accurate. And creative...pretty artsy (and by your own logic, weird?) of you.

Engineering is the practice of the art of science - Steve

 

[Artisi]

As with all new installation problems assume nothing, check everything.

CHECK:
The following points first-up;
1. motor direction, and motor current for later use.
2. check for inlet pipe work blockages
3. check for discharge pipe work blockages (including air entrapment at the high point)- vent it if possible - eliminate the problem.
4. are all valves fully open?
5. measure inlet and discharge pressures and flow rate - compare to the pump performance test curve - is it on curve somewhere- does power input agree with the curve?
6. recalculate total head - does this confirm original data?
7. has the pump been correctly sized using your recalculated flow/head figures?

These are a few basic checks - you might feel a bit stupid rechecking some of them - but better at this point than later.

 

[ccfowler]

You would do well to add one item to Artisi's list. Verify the proper calibration of all instrumentation.

 

[dcasto]

FACS and LHA, nice volleys, Lets pick this up on the Where is engineering going forum... I can teach monkeys to follow specifications, it takes an artist to expand upon nature and produce something....

 

[BigInch]

Where are those highly valuable monkeys?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com