Bendix Commercial Vehicle Systems BA-921 SMC COMPRESSOR - Manual (Page 6)

6
SERVICE TESTS
GENERAL
The compressor operating and leakage tests listed below
need not be performed on a regular basis. These tests
should be performed when it is suspected that leakage is
substantially affecting compressor build-up performance,
or when it is suspected that the compressor is “cycling”
between the loaded (pumping) and unloaded (non-
pumping) modes due to unloader leakage.
IN SERVICE OPERATING TESTS
Compressor Performance: Build-up Test
This test is performed with the vehicle parked and the
engine operating at maximum recommended governed
speed. Fully charge the air system to governor cut-out (air
dryer purges). Pump the service brake pedal to lower the
system air pressure below 80 psi using the dash gauges.
As the air pressure builds back up, measure the time from
when the dash gauge passes 85 psi to the time it passes
100 psi. The time should not exceed 40 seconds. If the
vehicle exceeds 40 seconds, test for (and fi x) any air leaks,
and then re-test the compressor performance. If the vehicle
does not pass the test the second time, use the Advanced
Troubleshooting Guide for Air Brake Compressors, starting
on page A-1 of this document to assist your investigation
of the cause(s).
Note: All new vehicles are certifi ed using the FMVSS
121 test (paragraph S5.1.1) by the vehicle manufacturer,
however the above test is a useful guide for in-service
vehicles.
Optional Comparative Performance Check
It may be useful to also conduct the above test with the
engine running at high idle (instead of maximum governed
speed), and record the time required to raise the system
pressure a selected range (for example, from 90 to 120 psi,
or from 100 to 120 psi, etc.) in the vehicle’s maintenance
fi les. Subsequent build-up times throughout the vehicle’s
service life can then be compared to the fi rst one recorded.
(Note: the 40 second guide in the test above does not
apply to this build-up time.) If the performance degrades
significantly over time, you may use the Advanced
Troubleshooting Guide for Air Brake Compressors, starting
on page A-1 of this document, to assist investigation of
the cause(s).
Note: When comparing build-up times, be sure to make
an allowance for any air system modifi cations which would
cause longer times, such as adding air components or
reservoirs. Always check for air system leakage.
LEAKAGE TESTS
See the standard Air Brake System and Accessory Leakage
test on Page A-14 (Test 2).
Note: Leakage in the air supply system (components
before the supply reservoir such as the governor, air dryer,
reservoir drain cocks, safety valve, and check valves) will
not be registered on the vehicle dash gauges and must
be tested separately. Refer to the various maintenance
manuals for individual component leakage tests and the
Bendix “Test and Checklist” published in the Bendix
Air
Brake System Handbook (BW5057) and on the back of
the Bendix
Dual Circuit Brake System Troubleshooting
Card (BW1396).
CYLINDER HEAD
Check for cylinder head gasket air leakage.
1. With the engine running, lower air system pressure to 60
psi and apply a soap solution around the cylinder head.
Check the gasket between the cylinder head and valve
plate assembly, as well as the inlet reed valve/gasket
between the valve plate assembly and crankcase for
air leakage.
2. No leakage is permitted. If leakage is detected, replace
the compressor or repair the cylinder head using a
genuine Bendix
® maintenance kit available from an
authorized Bendix ® parts outlet.
INLET, DISCHARGE & UNLOADER
In order to test the inlet and discharge valves and the
unloader piston, it is necessary to have shop air pressure
and an assortment of fi ttings. A soap solution is also
required.
1. With the engine shut off, drain ALL air pressure from
the vehicle.
2. Disconnect the inlet and discharge lines and remove
the governor or its line or adapter fi tting.
3. Apply 120-130 psi shop air pressure to the unloader
port and soap the inlet port. Leakage at the inlet port
should not exceed 50 sccm.
4. Apply 120-130 psi shop air pressure to the discharge
port and then apply and release air pressure to the inlet
port. Soap the inlet port and note that leakage at the
inlet port does not exceed 20 sccm.
If excessive leakage is noted in Tests 3 or 4, replace or
repair the compressor using genuine Bendix
® replacements
or maintenance kits available from any authorized Bendix
parts outlet.