3 different points on pump curve...not adding up? 1

[Engineering1012]

Hello,

I have 3 vertical sump pumps at our plant. I've been having trouble finding where it runs on its curve and need some advice. I took amp readings (converted to bhp), NEW gauge dP readings, and downstream flow meter readings, and none of the points really line up on my curve. Any hunches on what this could be? Air entrapment/vortexing? Dirty suction?...etc? Any advice or tips would be great for a young reliability engineer. I can provide more information if needed.

Thanks!

Frank

 

[LittleInch]

http://www.pumpfundamentals.com/help11.html

Check this link



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[Artisi]

Where is the water in the sump coming from, is it aerated, is it free-falling into the sump and driving air into the sump?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Engineering1012]

The liquid is gravity fed from the areas walkways into the sloped sump. It's most water but debri from all over can make its way in there. The liquid travel through screens and into the settling chamber where the level rises and dumps over a weir into the pumping chamber. I imagine there is some air entrapment with the water flowing near the suctions

 

[Artisi]

If the water is flowing over a weir you can bet there is air being entrained into the sump, depending on sump size, retention time etc it could be a major problem with the flow into the pump inlet - depending on the pump design, a few percent of air could be sufficient to cause problems of poor hydraulic performance.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[bimr]

Mag meters should be installed with full liquid flow in the pipe. Do you have an air release device in the piping.

 

[Latexman]

At 275 gpm there will be many sections (I see some 10" and 12" sections) that are not pressure flow or full-flow. It will be free-surface flow. What methodology did you use for head loss on those sections? Or, did you assume they were all hydraulically full? The flow would have to be 3,000 and 5,000 gpm to fill horizontal sections of 10" and 12" pipe, respectively.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[cvg]

it appears from the sketch that the pipe rises 35 feet before dropping to the outfall. so that pipe would be completely full, assuming the check valve works, there would not be a free surface. there may be air in that high point though. given the large pipe and low flow, the velocity would be less than 1 foot per second, not enough to move most sediment which could be blocking the low, flat areas of the pipe also. Your pipeline should be about 4 - 6 inch diameter, not 12

 

[Latexman]

Yes, I was thinking of the "over 1000 ft . . . " downstream of the "highest point" to the "lower ground" outfall.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[cvg]

downstream of the high point appears to be hydraulically disconnected from the upstream force main. it appears to be basically a gravity line. But given the level of detail in the sketch, it is hard to tell for sure.

 

[Engineering1012]

There are a ton of lines that tie into this main lie before dumping into that atmospheric tank (that's what all those arrows are representing). I have a lot to start digging into now with all of your responses. Air entrapment could be our main culprit in all of this..

 

[Artisi]

When all the crystal ball gazing is over and as you are trying to establish the pump performance, all you need to so is carefully measure the pump performance in terms of flow and head at or near the pump discharge not away in the distance some place where the pipe might not be running full, what is happening downstream of the pump you can treat as irrelevant to the pumps performance.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

Should add,test the pumps at a number of heads and flow rates at or near to the pump -- run an on site performance test , log the results and draw a performance curve.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Just please respect us and come back and tell us what you found, good or bad, and if you solved the problem / issue.

Even 2 months later.

Thanks LI.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Engineering1012]

My issue with some of the testing is I am not exactly sure what values I need to be trusting. My amps, dP, and flowrate are not aligned which is why I am having issues with evaluating the performance. And of course I'll keep to forum updated, this was a project that got put on hault, and then came back again...I believe I am getting suction issues.

 

[LittleInch]

Start by checking and confirming the things which can be verified.

For me this would be:
Levels and vertical measurements - t's difficult to misread a tape measure.
Pressure gauges / transmitters (easy to calibrate off line) - make sure you're at between 30-70% of range for best repeatability
Amps are fairly standard as are volts so you can be pretty sure about those, but again could be removed and calibrated or duplicated if you want to be sure.

Flowrate is a little harder to be certain of, especially if there is air involved. Any chance you could set up a single pump divert to a known volume tank and measure volume over time, then switch back to the main line?
The latter would also let you know if there is air entrained as well.

Good luck!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[curtis2004]

Frank217,

1. One thing I have noticed is, you have 8" line and pump and have only 4' submergence (which could be even smaller) inside suction tank. Is you pump not big for its application?
2. Your flow meter reading could be not correct, due to half flow or low flow.

Curtis

 

[Engineering1012]

1. I believe 4' submergence is more than adequate for a vertical sump pump. What are you calculating it at?
2. And that may be true but it its low flow that doesn't match up with the discharge pressure I am getting either...