AIR COMPRESSOR (cont)
CENTRIFUGAL UNLOADER (MODEL 20-904)
The centrifugal unloader releases pressure from the high pressure cylinder of the compressor until the electric motor is
running close to full speed.
The electric motor draws more current when it is first starting up than when it is running full speed. It also draws more
current when it works against a load such as compressing air as when it is running without a load. The unloader prevents
big current surges in the motor by unloading it during start up.
Here is how the unloader works: When the compressor is standing still or rotating at a low speed the fingers on the
weights C push in on plunger B.
The plunger pushes on valve D and causes it to release the pressure from the cylinder head. When the compressor
reaches normal speed, the centrifugal force causes the weights C to pull outward. This takes the pressure off the plunger
B, the valve D closes and the compressor builds up pressure.
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