BENDIX BA-921 COMPRESSOR-STD-CLOSED ROOM Dati di servizio - Pagina 5
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minimum required reservoir volume for the vehicle. This test
is performed with the engine operating at maximum recom-
mended 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 com-
pared to the base line new compressor performance.
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 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 re-
pair 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, air dyer, reservoir drain cocks,
safety valve and check valves can leak with-
out indication on the dash gauges. These
components must be checked for leakage
separately and individually. Refer to the vari-
ous 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 plate assembly and the reed valve/gasket between
the valve plate assembly and cylinder block for air leak-
age.
2. No leakage is permitted. If leakage is detected replace
the compressor or repair the cylinder head using a genu-
ine Bendix maintenance kit available from an authorized
Bendix parts outlets.
Unloader
In order to test the inlet and discharge valves and the un-
loader piston, it is necessary to have shop air pressure and
an assortment of fittings. A soap solution is also required.
Build-Up tests
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 2 with previ-
ously recorded build up times to evaluate compressor
performance.
Unloader leakage is exhibited by excessive compressor
cycling between the loaded and unloaded condition.
1. With service and supply system leakage below the maxi-
mum allowable limits and the vehicle parked, bring
system pressure to governor cutout and allow the en-
gine to idle.
2. The compressor should remain unloaded for a minimum
of 5-10 minutes. If compressor cycling occurs more fre-
quently and service and supply system leakage is within
tolerance replace the compressor or repair the compres-
sor unloader system using a genuine Bendix
maintenance kit available from authorized Bendix parts
outlets.
COMPRESSOR REMOVAL & DISASSEMBLY
GENERAL
The following disassembly and assembly procedure is pre-
sented for reference purposes and presupposes that a rebuild
or repair of the compressor is being undertaken. Several
maintenance kits are available and the instructions provided
with these parts and kits should be followed in lieu of the
instructions presented here.
MAINTENANCE KITS & SERVICE PARTS
Cylinder Head Gasket Kit.
Unloader Kit.
Governor Adapter Kit.
Safety Valve.
Seal Kits.
All components shown in figure 9 with a key number are
available in kits and/or as individual service parts.
IMPORTANT! PLEASE READ:
When working on or around a vehicle, the following
general precautions should be observed:
1. Park the vehicle on a level surface, apply the park-
ing brakes, and always block the wheels.
2. Stop the engine when working around the vehicle.
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