Estimating water flow/usage with pump curves

[wrightj7]

Hello,

I am very new/know nothing at all about pumps, so I sincerely apologize for the stupidity that is about to be spread all over this page. I currently have pump curves showing head (ft) and Eff (%) vs. flow rate (gpm). As well as a power line (hp) at the bottom. I know time and several other parameters of the pumps themselves, such as pipe diameters, pipe length, total head, discharge pressure.
So I guess my questions is, what other information do i need in order to estimate monthly water use from a pump that say I know runs 20 hours a day. Amps, hp, voltage? I have no idea. And no, I don't have a flow meter available. Sorry. Any information would be appreciated, thanks.

 

[BigInch]

Two things you can do. Plot the system curve and the pump curve. The average flowrate should be somewhere around the "system operating point", intersection of the two curves. From that you can check to see if the pump is still properly sized, as its BEP flow and head should correspond to that same operating point. If not, some changes might be suggested.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[wrightj7]

Ok, I understand that, but where do I get a system curve? Is that something the manufacturer provides, or I have to create based on my system? Thanks again.

 

[BigInch]

You gotta' do that. Its equal to the injection pressure (actually its equivalent head) needed to get into the downstream piping plus head lost when flowing through valves, fittings and pipe between the pump and the injection point.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[JRLAKE]

Think of the system curve as a route between you and your grandmother's house. Asking the pump manufacturer to provide a system curve is like calling your car manufacturer and asking them how long it will take to drive to Granny's.

 

[Artisi]

From what you have said it seems that you have the operating discharge pressure. If this is what you have then convert the pressure into feet of head, add or subtract the head on the inlet side of the pump, if a positive head subtract if a negative (lift) add this will give you the total head across the pump, them locate this point on the head scale -project across until you intersect the H/Q performance curve, at this point project down to the flow scale - this will give you an indication of the flow rate. As a check you need to convert the amp input to the motor into horsepower which should include the motor inefficiencies so that you are calculating output power of the motor- then check this against the power input shown on the pump performance curve.

This should give you a reasonable answer for the pump output, as a further check follow BigInch's suggestion by calculating a head / system curve for the pipeline and compare the two results.

 

[wrightj7]

Attached is all the information I have. I'm not sure if I can do anything with this or if I need more. Thanks.

http://files.engineering.com/getfil...-cd68-4668-b6ce-76d833603be6&file=863_RPM.pdf

 

[BigInch]

Looks like 2200 gpm was the design point. I'd say all you can logically do is assume that the design point was correct and use that as the average flow (if not actual). Multiply by 20h/24h to get daily flow volume * 30.4 for monthly volume.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[quark]

The manufacturer calculated the operating point for you, what else do you want? The system resistance calculated is OK (presuming the flowrate, pipe length and fitting details are correct)

 

[Artisi]

You have the curve and the printout of the slurry derating calculation etc - so what are you asking, do you want to check the actual site performance against the pump curve or are you only pumping clear water.

If it's a slurry duty it is extremenly difficult to give an accurate flow rate without some means of measurement as the solids load and density is very changeable, this has a major effect on the pump performance - unless of course you have a tightly controled feed system into the pump.

For a slurry pumping application, the performance should be a measure of the amount of solids pumped over a given period - a minute by minute pump performance is really a bit meaningless unless you are measuring solids and density at exactly the same time.