How much water flow at low speed?

[mas985]

Two speed pumps run at typically 3450 and 1725 RPM on the motor. This doesn't necessarily mean 1/2 the gpm flow rate. The actual ratio 1/2 to full speed would depend on the centrifugal pump design and I have no idea how to calculate that and even if I did at one time in fluid dynamics class, it would have been long, long forgotten. It would be true in positive displacement pumps that are of a cylinder/piston or gear design. The actual flow and power consumption characteristics should be specified at each speed by the manufacturer.
Al

Actually, it is pretty close to 1/2 and it is based upon hydraulics equations. Approximation? Yes, but it is pretty close. These equations are generally refered to as pump affinity equations and can be read about here:

http://en.wikipedia.org/wiki/Affinity_laws

or more detailed here:

http://www.pumped101.com/pumpintro.pdf


and many other sites as well.