Pumps used in pools and spas are centrifugal type pumps.  Water is pulled into the center end fitting, called the suction, and sent out through the exit fitting, called the discharge.  In virtually every implementation the discharge is at a 90 degree angle from the suction.  There are a few exceptions in this, namely the Aqua-Flo® pump that is used in older 'Mr Spa' applications, and some Acura® spa pumps.  The flow-isolator shown above, is not on all pumps, and is used to allow a higher pressurization of the pump cavity.  Without it, the output from the impeller will feed back into the suction, reducing pump output.

Rotation speed is counter-clockwise (viewed from the front), typically 3450 RPM in a single speed pump, and 1725 and 3450  RPM in a two speed version.

Pump motors are brushless, and the rotation speed is primarily dependent upon the line frequency of 50 or 60 Hz.  Because of this design, the speeds can't be changed since the pump is 'hardwired' for these specific speeds of operation.

The diagram above uses a 48 frame through bolt motor, which is the most frequently used in the spa industry.

Motor manufacturers: A.O. Smith®, Emerson®, Franklin Electric®, General Electric®, and Magnetek®.

The business end of the spa pump, the part that moves the water, is called the 'wet end'.

All 48 frame through bolt motors, with a threaded shaft, are generally interchangeable among different manufacturers.  That is, if you remove the wet end from a GE motor, you can re-install it on any of the other manufacturers pump motors with a similar horsepower rating.

The most commonly found problem in existing spa pumps, is the failure of the pump seal assembly, located between the impeller and the volute (back of the wet end).  The end result is usually the destruction of the impeller because of rust creeping back up the shaft, and in severe cases, the pump bearing will fail, requiring replacement of the bearing or the motor. 

The cause for seal failure is usually the lack of proper water quality management.