Pump Flow VS Pump Motor Amp 1

[Brian2903]

I am wondering if there are any relationships to descript pump motor Amp and actual pump flow. That is by measuring the pump motor Amp to eatimate the actual pump flow.

Thanks!!

 

[BigInch]

In a steady state situation, I think you can get very close, given a bit of history.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[miningman]

I suspect everyone here is missing the most relevant point. Pump curves are obviously developed on the basis of a brand new pump. Any normal wear within the pump essentially means that you are using a different pump and different curve. From memory, power required is a function of the flow rate and the square of the head. For a worn pump, the flow rate drops as well as the head that the pump can develop so there is an effective cube relationship between power and flow on different pumps... and a worn pump is a different pump from the same model in new condition.

How would one know whether a given installation is a new unit operating at design or a worn unit operating at only a fraction of its design parameters?. The cubic relationship between flow and power throws this into disarray does it not??

 

[electricpete]

I suspect everyone here is missing the most relevant point.

miningman - Please read a few things:

1 - First check out Artisi's post 20 Jul 08 1:12

2 - Then check out the original post:

That is by measuring the pump motor Amp to estimate the actual pump flow.

3 - Then check out the definition of estimate

http://www.thefreedictionary.com/estimate

es·ti·mate
tr.v. es·ti·mat·ed, es·ti·mat·ing, es·ti·mates
1. To calculate approximately (the amount, extent, magnitude, position, or value of something).

Then after reading those, you want to come back and affirm your criticism of everyone else who came before, please do. Until then, I will assume you simply didn't read the original question.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[miningman]

I might apologise to any previous poster who reads criticism into my previous post but there was absolutely no intent to imply any such criticism. The original poster Brian identified himself as civil / environmental and I might be forgiven for thinking that neither pumping nor electrical engineering are his prime areas of expertise.

There is a huge difference in the theoretical practice of engineering and the use of the same principles to solve problems in the field. Personally I have run several pumps to the point where discharge volume was zero, because of internal wear. I also have first hand knowledge of an individual refusing to reverse the rotation on three phase submersible pumps that were not producing the theoretical flow rate .... the argument being that he had done the calculations and in his opinion, said pump could not function at a specific head....... this despite the fact that I had specced, sourced and used the same pumps only a few weeks earlier at much greater heads.

English is my mother tongue and I need no assistance in the definition of commonly used words, and my background allows me to very easily imagine circumstances when a given unit is pulling only 30-50% of its rated load and producing anywhere from 0-50% of theoretical flow... ie absolutely no correlation whatsoever in the field.

When I have posted queries in this forum I have recieved suggestions ranging from exactly what I was looking for, to suggestions that were useless or irrelevant, and in the mid point, ideas which of themselves were not relevant, but which generated ideas which later proved to be productive.

I never criticised posters who provided suggestions that were less than usefull to me since they obviously believed it worthwhile to try to help. If Brian2903, or anyone else wants to consider my ideas, fine. If he wants to ignore my ideas, I will lose zero sleep over it.

What I tried to do was provide suggestions based on 30 years experience in the field which might have a slightly differing point of view to anyone whose background is essentially office and /or consultancy. Electric Pete obviously has a low opinion as to the relevancy of my experierence...This will be my last post in this particular forum.

 

[electricpete]

Electric Pete obviously has a low opinion as to the relevancy of my experierence

I said nothing about the relevancy of your ideas or experience. I was pointed out that the brand new idea you seemed to think you were bringing had (from my perspective) already been covered ad nauseum within this thread.

I apologize if my tone offended you.



=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

Might I also add that you should in general expect some reaction when you come into a thread with 21 replies over 6 weeks and lead off with a statement "I suspect everyone here is missing the most relevant point."

You may not have intended it to sound like criticism, but that's what it comes accross as.



=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[dabluffrat]

Yes, it can be done as it was addressed above before everyone got off topic... but it is difficult. If knowing the exact flow is critical, I would look into the flow meters mentioned above.

Couple of things to consider I didn't see already mentioned:

1. Are you measuring balanced 3 phase amps or a single leg?

2. Synchronous or induction motor? Synchronous motors are rare, but used. As the power factor setting moves away from unity, the amps will increase (the V curve).

3. Pump wear over time will cause a decrease in efficiency and increase in amps. You will lose flow as you increase amps.

4. Using typical motor and pump data vs actual test data for your power and BHP calculations. Name plate efficiency is only for the rated full load HP. It's difficult to find actual (accurate) test data on older pumps.

 

[waross]

This is getting a little off topic. Posters are responding to other posters rather than going back and reviewing the original post.
The original poster asked

I am wondering if there are any relationships to descript pump motor Amp and actual pump flow. That is by measuring the pump motor Amp to eatimate the actual pump flow.

OK, I measured the pump motor amp. My pump is drawing 40 amps. What is the flow rate??
I think that is the point that we are missing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MikeCool]

I'm a pump designer and manufacturer (

http://www.aspumps.com).

In testing our pumps to confirm design intent, we measure flow rate, total dynamic head, input voltage and amps, rpm, and torque. Some of these measurement are redundant, but they serve as comparable data, and some measurements are more accurate than others.

In testing to see that production models are performing to specifications, we measure flow, TDH, volts and amps.

In order to determine the pump flow rate, when all we can measure are the motor amps, we must have certified pump and motor performance curves corrisponding to the particular rpm and voltage. The amp data is used to determine the input motor horsepower to the pump from the motor performance curve, and then the motor BHP is used to determin the pump flow rate on the pump performance curve.

This method is as accurate as your measurements and factory performance curves. As Johnny Pellin stated earlier, some pump can have a hump in their performance curves, which obfiscates the solution. If this is the case as can be detemined by the pump performance curve, you need additional data: suction and discharge pressure.

Good luck!

Mike Cool
Mechanical Engineer
American Stainless Pumps, Inc.
Los Angeles California USA

http://www.aspumps.com

 

[Artisi]

dabluffrat.
This is off topic but I believe that incorrect information stated in your last posting should be corrected for the benefit of those who believe that eveything on the net is gospel.

" 3. Pump wear over time will cause a decrease in efficiency and increase in amps. You will lose flow as you increase amps."

A reduction in performance for a fixed speed pump eg, less flow and / or less head, usually a combination of both due to internal wear (decrease in efficiency)results in a lower power input(less amps) not more. However, if the pump unit is variable speed drive and the speed is increased to overcome the lower hydraulic efficiency of the impeller due to wear, then and only then will the power input increase.