On Fri, 3 Apr 2009 17:43:36 -0500, "Karl Townsend"
wrote:

I just bought a trash pump without the gas engine.
http://tinyurl.com/d3qj5f

What RPM do I spin it at?

FWIW, I hate small gas engines. Nothing but trouble. I'll use a 3 phase
motor for this job.

If you want to use an electric motor you can go a bit smaller - If
it calls for 5.5 HP gas engine, you can probably drop to a real 3 HP
electric motor - a 5 HP would spin it without breaking a sweat.

For some reason small gas engines are rated at gross HP, and when you
subtract the power used to run the cooling fan...

And find out the optimum speed for the pump head - probably 2,400
RPM to 3,600 RPM range common for gas engines.

This style pump head is meant to direct-mount onto a certain tapered
crankshaft tail normally found on gasoline engines - which you are NOT
going to find on regular electric motors. The pump impeller has the
female of the tapered shaft with the lockbolt, and the tolerances when
it's all bolted together is critical.

Pool pumps and stationary pressure pumps are built to bolt to a
standard C-face pump duty motor with straight keyway shaft, not these.
If you search, you can probably find a semi-trash style pump made for
an electric drive - just like you can find prerssure washer pumps
built both ways.

If you really want to go electric with that particular pump head,
you need a pedestal adapter for the pump. It has the proper tapered
shaft with center bolt, a pedestal in the middle with two shaft
support bearings and and bolting face at one end to mount the pump, a
mounting foot built into the casting, and the other shaft end has a
straight shaft with keyway to mount a standard drive pulley or a
Lovejoy Coupling.

Thern you vary the pulley ratios to drop the speed a bit from the
3,450 RPM of the electric motor to the ~2,400 RPM that the pump head
really wants.

-- Bruce --