On Mon, 15 Sep 2008 09:00:13 -0500, "Karl Townsend"
wrote:



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


Before you change the prop, try wiring in the VFD and seeing if you can get a
decent flow at a lower speed with the existing setup. If it's either
cavitating or (worse) pulling in air, it may well pump better at lower speed
anyway.

Is the lead in to the prop properly streamlined and gently divergent? Pressure
drop before the prop is your enemy. Higher net-positive-suction-head is your
friend to avoid cavitation.

Mark Rand
RTFM