REPAIR OF AIR COMPRESSOR
a. General. The pilot valve senses air receiver
a. The air compressor is a two-cylinder, two-stage,
tank pressure, and when the pressure is raised to a
vertical, air-cooled, V-belt driven unit. It will deliver
predetermined setting (approximately 175 psi) air is
15 cfm (cubic feet per minute) at 175 psi (pounds per
released to the head unloaders. The head unloaders
square inch) when driven at 735 rpm (revolutions per
are intake valve hold-open mechanisms. When the in-
minute). Constant speed unloading is provided. Con-
take valves are held open, the compressor stops com-
stant speed operation allows the compressor to run
continuously without stopping or starting the engine
pressing air and runs freely until the pilot valve
after each cycle. The compressor stops compressing
senses that the pressure in the tank has dropped to
air and runs free until the pressure in the air receiver
the predetermined setting (approximately 145 psi).
At this time the air is released from the head
has dropped to a predetermined setting at which time
unloaders, the intake valves are released, and the
the compressor starts compressing air again until the
compressor again starts compressing air. The pilot
pressure reaches its predetermined limit.
b. Removal of the compressor from the lubricating
valve is designed to function as an automatic on-and-
off air switch. A sensing tube from the air receiver
tank to the bottom of the pilot valve allows pressure
to act on the bottom of the valve. When pressure is
great enough to overcome the spring force holding
7-2. Compressor Flywheel.
the valve down on the lower seat, it lifts off the seat
and allows air to flow around the valve and out
(1) Loosen nut (1, fig. 7-2) and bolt (2). Pull
through side ports. One port opens to the head
flywheel (3) from end of crankshaft. It may be
unloaders, the other to the pneumatic cylinder and
necessary to pry apart slightly the split in the hub to
throttle control on the engine. When the valve lifts
off the lower seat, it moves up and seats on an upper
(2) Remove key (4).
valve seat where it is held by tank pressure. When
pressure falls, the valve spring- forces the valve back
b. Cleaning and Inspection.
down onto the lower seat. Air from the lines to the
(1) Clean all parts with dry cleaning solvent (fed.
head unloaders and throttle control escapes through
spec. P-D-680). Dry thoroughly.
the upper seat in the pilot valve and out through a
(2) Inspect the flywheel for cracks, chips, distor-
vent hole. The pressure at which the valve is on or off
tion and wear, Inspect V-grooves for rough or chipped
is controlled by the spring force. A small adjustment
areas where excessive wear to the V-belts could oc-
can be made on the spring force by compressing the
cur. File off all burrs.
spring more or less with an adjusting screw provided
(3) Replace all defective parts.
on the pilot valve.
c. Installation. Install the flywheel as illustrated in
and proceed as follows: