A.O. Smith ST1302 Manual page 16

14
T1072
JET PUMP MOTOR
Level 2
Most jet pumps use NEMA C face (56C or 56J)
or square flange motors. Most square flange
motors have 1/2-20 threads but some have 7/16-
20 threads. Many other centrifugal pump appli-
cations such as lawn sprinklers and irrigation
use jet pump type motors.
Jet pump motors typically have shielded bear-
ings while swimming pool pump motors have
sealed bearings. Both types of bearings are per-
manently lubricated and neither is waterproof.
Running a pump dry does not harm the motor
which is actually operating at a very light load.
However, if the seal is damaged by the dry oper-
ating condition, it will leak and probably allow
moisture into the motor bearing.
Jet pumps operate on the principle of centrifu-
gal force. The motor spins the impeller which
does the work.
Jet pumps get their names from the principle of
operation in which a stream of water is pushed
through a nozzle into a diffuser creating an area
of low pressure. This low pressure draws addi-
tional water from the supply (usually a well).
The action of getting water from the well into
the pump system is caused by air pressure. At
sea level, air has enough pressure to lift a column
of water thirty-four (34) feet. Because of differ-
ences in air pressure, elevation and system effi-
ciencies, most jet pumps have an arbitrary lift
rating of twenty-five (25) feet.
Pump Motors
A.O.Smith