Pond Boss Forums STOCKING A NEW POND Types of fish to choose 300 Gallon Plastic totes??

The correct spelling is rheostat. Barring info from someone who actually knows, you may find the following speculation of use.

A rheostat is a variable resistor, which would be used to attempt to control pump output by reducing the supply voltage from the nominal 110/115/120 VAC without changing the sinusoidal waveform. A variac (variable output transformer, 110 VAC in and dial-an-output) would have the same affect, without having to worry about the rheostat's power rating.

IME, single phase motors subjected to lower than normal voltage input (with the regular sinusoidal waveform) either get enough power to start and then run (apparently) normally, or won't start at all. The reduced voltage level which will enable them to start is load dependent, i.e. 92 VAC would start a motor having a light initial load, but not with a heavier load. With a pump, I think this load cutoff point would be based on the water pressure the pump is supplying.

If the motor gets so little voltage (wrt it's load) that it cannot start, IME being in this partial-power-supplied-but-not-enough-to-start state willl not damage the motor in the short term. I personally have not cared to leave a single phase motor plugged in to such insufficient voltage for long enough to determine long term affects. I have run an single phase air compressor with low voltage (apx. 92 VAC) for several hours accumulated over a period of several years without any (apparent) ill affects.

Solid state dimmers, as have been commonly used to control incandescent lighting levels, reduce supplied power by chopping out a portion of the waveform, changing it's shape from the normal sinusoidal form. These should only be used for resistive loads and would likely be very bad news for a motor.