12.4 Air Compressor
DETROIT DIESEL 53
As each piston starts its downstroke, the discharge
Service Note
valve above it returns to its seat, preventing the
compressed air from returning to the cylinder and the
When installing the drive hub on a flange mounted air
same cycle is repeated.
compressor (Fig.1), it is important the 3/4 "10 drive shaft
slotted nut be tightened to 100 lb-ft torque minimum
When the air pressure in the reservoir reaches the
before installing the 3/32 "x 1 1/4 " cotter pin.
maximum setting of the governor, compressed air from
the reservoir passes through the governor into the cavity
The air compressor drive shaft will turn during the
below the unloading pistons in the compressor cylinder
torquing operation unless some provision is made to
block. The air pressure lifts the unloading pistons which
hold it. One way this can be done is to weld a modified
in turn lifts the inlet valves off their seats.
drive coupling to a support or base which in turn can be
anchored to the mounting flange of the compressor. An
With the inlet valves held off their seats, the air during
old flywheel housing cover that matches the flange of
each upstroke of the piston is merely passed back
the compressor makes an ideal base for the modified
through the air inlet cavity and to the other cylinder
coupling. With the exterior splines of the coupling in
where the piston is on the downstroke. When the air
mesh with the internal splines of the drive hub and the
pressure in the reservoir drops to the minimum setting
entire assembly secured to the compressor housing, the
of the governor, the governor releases the air pressure
hub and shaft are kept from rotating when the torque is
beneath the unloading pistons. The unloading piston
applied. That part of the base within the inner diameter
return spring then forces the piston down and the inlet
of the coupling must be removed to permit placement of
valve springs return the inlet valves to their seats and
the wrench socket on the nut. Two bolts will secure the
compression is resumed.
base to the compressor during the torquing operation
(Fig. 2).
1972 General Motors Corp.
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