Pump flow question 3

[StoshM]

We need to determine the output of a centrifugal pump. The problem is that there are no pressure gauges to determine the dP across the pump, and no flowmeter downstream. The manufacturers pump curve has horsepower included. Is it "acceptable" to determine flow based on motor amperage?

StoshM

 

[spayette]

Yes. I have used this technique a number of times. However, in order to perform an accurate calculation you will also need to know the voltage, power factor, installed impeller diameter, rpm, and motor efficiency as well as have a copy of the pump performance curves.

 

[TD2K]

Anything is 'acceptable' if you are understand and are willing to accept the potential errors in your estimation. Most Hp curves I've seen on centrifugal pumps are flatish meaning that relatively small errors (eg. estimating the motor's efficiency to determine the pump BHp) can move the estimated flow rate significantly. I realize the same could be true of using the pump's dP. And in either case, you are making the assumption the pump is operating per the manufacturer's curve, that no significant amounts of internal wear have occured, the installed impeller is the same size as that shown on the data sheet, etc.

Are there no drain or vent valves that you could install a temporary pressure gauge? That would give you a check against the Hp estimation.

Can you rent a portable ultrasonic flowmeter? I've used these on water lines and they are an excellent tool.

It comes down to how critical is this flow rate to you.

 

[StoshM]

We do have some areas with thread-o-lets and thermowells. We could install a temporary gauge. Renting a ultrasonic meter is an excellent idea. I will have to investigate that further. Thank you TD2K and sprayette for the suggestions.

StoshM

 

[d23]

StoshM:

Some of the problems with your consideration is fluid gravity, viscosity, motor load etc. Not know your application I would personally say no. There are applications where all the facts are known and motor amps would offer a reasonable guess, but I would not agree with amps unless I knew all the facts.

TD2K offers a great suggestion about renting a meter. I would recommend that.

D23

 

[olef]

Often the easiest way to measure flow is to measure differential in upstream or downstream tanks. Any possibility of that here?

Regards
OleF