RPM of Hydraulic Motor as an Indication of GPM?

[N8ghz]

I am wondering how accurate it would be to place a 1 cu.in. hydraulic motor on a source and checking it's RPM with a mechanical stem-tach to get close on flow settings? I wonder about average losses against theoretical. It seems to me that with 231 cu.inches in a gallon, that theoretically, 1 GPM would yield 231 RPM. Has anyone pondered or tested this? I have a few 1.0 cu.in. motors and could put a set of hoses & QC's on one of them for a test. I realize there will be some losses because of the hose size & the restriction of the QC's.....I just wonder how close it would be converting the RPM to GPM?

added: I don't have a flow-meter

 

[IceStationZebra]

If there is no back pressure on the motor it will be very accurate, probably within ~1%. Some flow meters use this type of arrangement. Just make sure you don't have air in the oil and don't overspeed the motor.

If there is some back pressure it will cause internal leakage and decrease the accuracy, but with a gear pump it will probably by <5% worst case. It all depends on the amount of wear, oil viscosity, motor speed, and pressure differential.

ISZ

 

[N8ghz]

I have the specs on the motor, and it can run 3000 RPM. I think that would require ~13 GPM. So....It'd be good upto that point, and that is a good range for alot of things. I intend to experiment with one. The motor would not be running anything, just itself.

Thanks for the affirmative thoughts.

John

 

[J_J]

If you have a 10 cu in pump/motor, if you turn it at 23 rpm, you will pump 1 gal.

1 rpm = 10.04 cu in

So for every 23 rpm you pump 1 gal

46 rpm = 2 gal

69 rpm = 3 gal

and so and so on

1 gpm , and 1 cu in motor = 231 rpm

462 rpm = 2 gal

693 rpm = 3 gal

and so on and so on

 

[N8ghz]

that's what I thought.... 1 cu.in = 231 RPM if putting in 1 GPM.

 

[N8ghz]

Well I just found a reasonably priced Lake Flow-meter on Flea-bay....1-10 GPM....So I can use it & check this theory out too if I want to.

There is one left if anyone wants one.

 

[MHarryE]

Depends on pump condition, quality, and pressure. At the factory test bench I have seen 85% volumetric efficiency at the 185 bar (about 2700 psi) we used it. With a direct to tank return line you won't be 100% but pretty close at no load.

 

[J_J]

I recently read something about a flow meter blowing up, and it had to do with a check valve in some flow meters.

So pay attention to the flow direction. If it has a check valve, do not reverse the flow.