TM 5-4310-373-14
b. CENTRIFUGAL UNLOADER. The centrifugal
sure cylinder of the compressor until the elec-
unloader releases pressure from the high pres-
tric motor is running close to full speed.
1. Weights
2. Sleeve
3. Plunger
4. Ball
5. Spring
Figure 1-3. Operation of centrifugal unloader
The electric motor draws more current when it is first
The plunger pushes ball (4) off of its seat and opens to
starting up than when it is running full speed. It also draws
release pressure from the cylinder.
more current when it works against a load such as com-
pressing air as when it is running without a load. The un-
When the compressor reaches normal speed, the centrif-
loader prevents big current surges in the motor by unload-
ugal force causes the weights (1) to move outward. The
ing it during start up.
fingers on the weights push sleeve (2) against spring (5)
allowing plunger (3) to release and let ball (4) close and
the compressor builds up pressure.
Here is how the unloader works: When the compressor is
not operating or rotating at a low speed, the fingers on the
c.
ELECTRIC MOTOR. The electric motor is a
weights (1) allow sleeve (2) to push against plunger (3).
three phase induction motor.
Figure 1-4. Electric motor schematic
The operation of a three phase induction motor depends on
230 VAC is connected across T1, T2, T3, which causes
two basic parts, the stator or stationary windings and the
current to flow in the stator windings and produce a ro-
rotor.
tating magnetic field. This magnetic field cuts across the
conductors in the rotor, inducing currents in the conduc-
tors.
The rotor does not have windings, but has metal bars
pressed into its frame which act as conductors of electrical
This causes a repelling force between the conductors and
current. The rotor does not have any external connections.
the magnetic field and causes the rotor to turn.
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