TM 5-3810-300-24&P-3
12.4
AIR COMPRESSOR
vacuum is created above the piston which unseats the
The air compressor (Fig. I) may be mounted on a
inlet valve and then allows air drawn from the air box in
bracket attached to the cylinder block of the engine and
the engine cylinder block or through an intake strainer to
belt-driven from the crankshaft pulley, or it may be
enter the cylinder above the piston. As the piston starts
flange-mounted to the flywheel housing and gear driven
the upward stroke, the air pressure on top of the inlet
by means of an accessory drive attached to the camshaft
valves, plus the inlet valve return spring force, closes the
or balance shaft gear.
inlet valve.
The air above the piston is further
A six bolt design air compressor mounting base,
compressed until the pressure lifts the discharge
mounting bracket and gasket are used on current
valve and the compressed air is discharged through the
engines equipped with a belt-driven air compressor.
discharge line into the reservoir.
Formerly, the air compressor was attached to the base
As each piston starts its downstroke, the discharge valve
and bracket with four bolts. When installing a new air
above it returns to its seat, preventing the compressed
compressor, it is recommended that the new mounting
air from returning to the cylinder and the same cycle is
parts be used to eliminate the possibility of the bracket
repeated.
loosening and causing oil seepage at the gasket.
When the air pressure in the reservoir reaches the
The air compressor runs continuously while the engine is
maximum setting of the governor, compressed air from
running.
While the compressor is running, actual
the reservoir passes through the governor into the cavity
compression of air is controlled by the compressor
below the unloading pistons in the compressor cylinder
governor which acts in conjunction with the unloading
block. The air pressure lifts the unloading pistons which
mechanism in the compressor cylinder block. The
in turn lifts the inlet valves off their seats.
governor starts and stops the compression of air by
loading or unloading the compressor when the air
With the inlet valves held off their seats, the air during
pressure in the system reaches the desired minimum or
each upstroke of the piston is merely passed back
maximum pressure.
through the air inlet cavity and to the other cylinder where
the piston is on the downstroke. When the air pressure
During the down stroke of each piston, a partial
in the reservoir drops to the minimum setting of the
governor, the governor releases the air pressure beneath
the unloading pistons. The unloading piston return
spring then forces the piston down and the inlet valve
springs return the inlet valves to their seats and
compression is resumed.
Fig. 2 - Typical Air Compressor with Drive Hub
Fig. 1 - Air Compressor Mounting
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