Calculating Water Flow For Axial Flow Pump

Propeller efficiency might be around 0.7, depending on lots of stuff.

Thanks.

But i was looking for something like a better way to approximiate the flow out of the impeller?

Look at the pump curve for the pump.

Call the pump manufacturer and ask them.

Put a flow meter on it.

Typically a "Bucket and Stopwatch" test is great for any pump with ports smaller than 2" on the output.

• Get a bucket of appropriate size. 5 Gal. - 10 Gal. - 50 Gal.?
• Have a stopwatch or timer ready.
• Turn on your pump and direct the flow outside of your bucket.
• At the same time, actuate your timer and direct your flow into the bucket.
• Time for one minute.
• Direct the pump flow out of your bucket and turn off pump.
• Measure the amount of water in your bucket.
• You now have an approximate GPM.

This is only an approximation as it does not take into account the restrictions of the piping that may be installed in your set-up.

Good luck.

Bryan

I have resorted to this method but in litres/second.

If you perform the test with the extant as built piping in the path of the test then it's right on the money.

You're correct. This method is very accurate when it is tested as built.

The pump manufacturer probably can. Do you know how to use a telephone?

You forgot that the hub diameter of the propellor has to be subtracted.

Crucial to the flow through any rotodynamic pump is the net positive suction head (NPSH) and the discharge head. Simple pitch and speed calculations are valid only where the head difference is negligible (ships are pumps inside-out - the calculations by Icemaster are propellor velocity calculations).

Rotodynamic pumps have flow/head curves for each rotational speed.

Which one did you order? Or what does the nameplate say?