With the inlet valves held off their seats by the
SERVICE CHECKS
unloader pistons and plungers, air is merely
pumped back and forth between the two cylinders.
INSPECTION
When air is used from the reservoir and the pres-
It is of the utmost importance that the compressor
sure drops to low pressure setting of the governor,
is taking in clean air. The air strainer must be prop-
the governor closes and in doing so exhausts the
erly installed and kept clean. If the compressor in-
air from beneath the unloader pistons. The unloader
take is connected to the engine air cleaner, super-
saddle spring forces the saddle. pistons and plung-
charger, etc., these connections must be properly
ers down and the inlet valves return to their seats.
installed and maintained.
Compression is then resumed.
Check compresor mountings to be sure they are
secure. Check drive for proper alignment, belt ten-
PREVENTIVE MAINTENANCE
sion, etc.
EVERY 100 OPERATING HOURS
Inspect oil supply and return
lines. Be sure these
OR AFTER EACH 5,000 MILES
lines are properly installed and
that the compressor
is getting the proper supply of
oil, and just as im-
Depending on operating conditions and experi-
portant, that the oil is returning
to the engine prop-
ence, service compressor air strainer. Remove and
erly.
wash all parts. Strainer element should be cleaned
or replaced. If the element is cleaned, it should be
Check water lines to and from compressor if a
washed in gasoline, methyl alcohol, or soap and
water-cooled type.
water. The element should be saturated in clean
engine oil then squeezed dry before replacing it in
OPERATING TESTS
the strainer.
Due to the many different types of air brake sys-
Check compressor drive alignment belt tension
tems found on the many different types of vehicles,
and note that all mounting bolts are securely
it is impossible to set up any specific series of tests
fastened.
to determine the serviceability of the compressor
on a vehicle. Familiarization with the vehicle and its
air system is the best judge. If the compressor fails
EVERY 1,000 OPERATING HOURS
to maintain adequate air pressure in the air brake
OR AFTER EACH 35,000 MILES
system of the vehicle, it usually denotes loss of
efficiency because of wear, provided leakage in the
Remove compressor discharge valve cap nuts
air system is not excessive. Oil pressure is another
and check for presence of excessive carbon de-
sign of excessive wear.
posits. Also, check the discharge line for carbon. If
excessive carbon is found in either check, the cyl-
inder head or discharge line should be cleaned or
AIR LEAKAGE TESTS
replaced.
Leakage past the discharge valves can be de-
tected by removing the discharge line, applying
shop air back through the discharge port and listen-
EVERY 3,000 OPERATING HOURS
ing for escaping air. Also the discharge valves and
OR AFTER EACH 100,000 MILES
the unloader pistons can be checked for leakage by
building up the air system until the governor cuts
Depending upon operating conditions and expe-
rience, disassemble compressor, clean and inspect
o u t , then stopping the engine. With the engine
stopped, carefully listen for escaping air at the in-
all parts thoroughly. Repair or replace all worn or
take. To pin-point leakage if noted, squirt soapy
d a m a g e d parts or replace compressor with a fac-
water around the unloader pistons. If there is no
tory reconditioned, repair-exchange unit.
noticeable leakage at the unloader pistons, the dis-
charge valves may be leaking.
IMPORTANT-Should it be necessary to drain
the engine cooling system to prevent damage from
If the compressor does not function as described
f r e e z i n g , water cooled compressors must be
above, or leakage is excessive, the compressor can
drained as both cylinder block and cylinder head
are water cooled. Use drain cock or remove head
be repaired, in which case the following informa-
and/or block pipe plugs.
tion should prove helpful.
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