User's Manual

7
COMPRESSOR & GOVERNOR UNLOADER
SYSTEM
Test and inspect the compressor and governor unloader
system for proper operation and pressure setting.
1. Make certain the unloader system contains both the
governor and synchro valve as illustrated in Figure 3.
2. Cycle the compressor through the loaded and unloaded
cycle several times. Make certain that the governor cuts
out at 130 psi (cut-in should be approximately 110 psi).
Adjust or replace the governor as required.
3. Note that the DuraFlo 596
™
compressor cycles to the
loaded and unloaded conditions promptly. This can be
defi nitely confi rmed by installing a test gauge in the unused
unloader port on the compressor and observing the
reaction during transition from the loaded and unloaded
condition. Air pressure should be applied and exhausted
with a distinct “snap action” with no appreciable lag for
buildup or release of pressure. If prompt action is not
noted, repair or replace the synchro valve.
SERVICE TESTS
GENERAL
The following compressor operating and leakage tests
need not be performed on a regular basis. These tests
should be performed when; it is suspected that leakage is
substantially affecting compressor buildup performance,
or when it is suspected that the compressor is “cycling”
between the load and unloaded modes due to unloader
plunger leakage.
OPERATING TESTS
Compressor Performance
Vehicles manufactured after the effective date of FMVSS
121 must have a compressor capable of raising air system
pressure from 85-100 psi in 25 seconds or less, with the
minimum required reservoir volume for the vehicle. This
test is performed with the engine operating at maximum
recommended governed speed. The vehicle manufacturer
must certify this performance on new vehicles with
appropriate allowances for air systems with greater than
the minimum required reservoir volume. As a less severe
alternative to running a high RPM test, a new compressor's
buildup time can be measured and recorded at high idle.
Subsequent testing throughout the compressor’s service
life can be compared to the base line new compressor
performance. Compressor buildup times should be
recorded and kept with the vehicle maintenance fi les for
reference. When testing compressor buildup times it is
essential that air system leakage be kept below the allowed
maximum for the vehicle type being tested. Before running
buildup tests, check the service and supply systems for
excessive leakage and repair as necessary.
Note: Supply system leakage is not displayed on the
vehicle dash gauges and must be tested separately.
Supply system components such as the governor,
synchro valve, air dyer, reservoir drain cocks, safety
valve and check valves can leak without indication
on the dash gauges. These components must be
checked for leakage separately and individually.
Refer to the various maintenance manuals for
individual component leakage tests and the Bendix
“Test and Checklist” published in the Air Brake
System Handbook (BW5057) for air system leakage
testing.
LEAKAGE TESTS
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 body assembly and the gasket between the valve
body assembly and cylinder block 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
authorized Bendix parts outlets.
Inlet, Discharge & Unloader
While it is possible to test for inlet, discharge, and unloader
plunger leakage it requires disassembly of the cylinder head
to accomplish. For this reason it is not recommended.
Inlet and discharge valve leakage can generally be
detected by longer compressor buildup and recovery times.
Compare current compressor buildup times with the last
several recorded times. Make certain to test for Air system
leakage, as described under Operating Tests, before
making a determination that performance has been lost.
1. With the engine running, lower air system pressure to
90 psi and raise engine RPM to 1800. Measure and
record the time required to raise system pressure from
100 psi to 130 psi. Run this test three times and use
the average time.
Note: This test should be run with the engine and
air system at normal operating temperature (i.e. not
cold).
2. Compare the average time recorded in step 1 with
previously recorded build up times to evaluate
compressor performance.