On Mon, 15 Sep 2008 11:16:18 -0500, RoyJ wrote:

Karl Townsend wrote:
My apple water bin dump uses a .5 horse 3 phase 220 VAC motor attached
by pulleys and belt to an outboard motor prop in a tube to pump water.
Maybe 1" head at 100+ GPM. I just measured the current draw on this
motor at 1.5 amp, 2.0 amp, and 2.2 amp with a clamp A-meter.

Its a 1725 RPM motor with 2.2 reduction to the prop, so the prop turns
about 800. Its a NOISY operation. The prop cavitates and pulls air
even with all the deflectors I can install to stop the vortex. (I've
only lived with it since 1988)

I bought a prop that will throw a guestimated 3 times the water per
revolution. There's no way to know until its installed. I have the
physical room to change the pulleys and get a 3.5 reduction or about
500 RPM. That's most likely too fast and too much water.

OK, now to the question. Will installing a VFD and running the motor at
50% speed have a good chance at working? Or, do I need a larger motor
and VFD? I want to move the same amount of water.

Karl


Sounds like you need to run a much lower pitch prop. If it is
cavitating, you are just wasting energy. Are you running it in a tunnel?
Pitch? Diameter?

Sounds reasonable to me. Lower pitch is like more reduction on the
pulley. If the noise comes from the cavitation then the lower pitch will
solve it. If the noise comes from vibration or gear noise just from
turning 800RPM then lower speed won't help at all, of course.

How noisy is it with no prop?




--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

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