Bendix Commercial Vehicle Systems DURAFLO 596 COMPRESSOR 10/04 - Manual (Page 7)

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COMPRESSOR DRIVE
Check for noisy compressor operation, which could indi-
cate excessive drive component wear. Adjust and/or replace
as necessary. Check all compressor mounting bolts and
retighten evenly if necessary. Check for leakage and proper
unloader mechanism operation. Repair or replace parts as
necessary.
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 ™ compressor cycles to the loaded
and unloaded conditions promptly. This can be definitely
confirmed by installing a test gauge in the unused
unloader port on the compressor and observing the re-
action 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 sub-
stantially 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 sys-
tem 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 maxi-
mum 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 perfor-
mance. Compressor buildup times should be recorded and
kept with the vehicle maintenance files for reference. When
testing compressor buildup times it is essential that air sys-
tem 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, reser-
voir drain cocks, safety valve and check valves
can leak without indication on the dash gauges.
These components must be checked for leak-
age 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 Sys-
tem 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 autho-
rized 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 re-
corded times. Make certain to test for Air system leakage,
as described under Operating Tests, before making a deter-
mination that performance has been lost.