valve, and on top of the piston (Fig. 4). As the piston
A nameplate is attached to the crankcase of all
starts its upward stroke, the air that was drawn in
compressors. It shows the piece number, type and
on the down stroke is being compressed. Now, air
serial number (Fig. 3). A nameplate with a black
pressure on top of the inlet valve plus the force of
background denotes a new compressor, whereas a
its spring, returns the inlet valve to its seat. The
nameplate with a red background designates that
piston continues the upward stroke and compresses
the compressor is a factory reconditioned unit. All
the air sufficiently to overcome the discharge valve
c o m p r e s s o r s are identified by the piece number
spring and unseat the discharge valve. The com-
which is the number to use when reference is made
pressed air then flows by the open discharge valve,
t o a particular compressor. The type and serial
into the discharge line and on to the reservoirs (Fig.
number is supplementary information.
5).
Figure 3
Compressor Nameplate
OPERATION
GENERAL
Figure 5
The compressor runs continuously while the
As the piston reaches the top
of its stroke and
engine is running but actual compression of air is
starts down, the discharge valve
spring returns the
controlled by a governor which stops or starts the
discharge valve to its seat. This
prevents the com-
c o m p r e s s i o n of air by loading or unloading the
pressed air in the discharge line
from returning to
compressor in conjunction with its unloading mech-
the cylinder bore as the intake
and compression
anism. This is done when the air pressure in the
cycle is repeated.
system reaches the desired maximum or minimum
pressures.
NON-COMPRESSION (Unloaded)
When the air pressure in the reservoir reaches
the high pressure setting of the governor, the gov-
ernor opens, allowing air to pass from the reservoir
through the governor and into the cavity beneath
the unloader pistons. This lifts the unloader pistons
and plungers. The plungers move up and hold the
inlet valves off their seats (Fig. 6).
Figure 4
INTAKE AND COMPRESSION (Loaded)
During the down stroke of the piston, a slight
vacuum created above the piston causes the inlet
valve to move off its seat. Atmospheric air is drawn
in through the compressor intake, by the open inlet
Figure 6
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