BENDIX BA-921 COMPRESSOR-STD-CLOSED ROOM Service Data - Page 2
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BACK / RETOUR
FIGURE 2 - BA-921 CRANKCASE COVER
OPERATION
The compressor is driven by the vehicle engine and func-
tions continuously while the engine is in operation. Actual
compression of air is controlled by the compressor unload-
ing mechanism operating in conjunction with a governor.
GOVERNOR
UNLOADER
PORT
RESERVOIR
COMPRESSOR
FIGURE 3 - BA-921 COMPRESSOR UNLOADER SYSTEM
AIR INTAKE (LOADED)
During the piston down stroke, a vacuum is created in the
cylinder bore above the piston. The vacuum causes the
inlet reed valve to flex open. Atmospheric air flows through
the open inlet valve and fills the cylinder bore above the
piston. See figures 4 & 7.
AIR COMPRESSION (LOADED)
When the piston reaches approximately bottom dead cen-
ter (BDC), the inlet reed valve closes. Air above the piston
is trapped by the closed inlet reed valve and is compressed
as the piston begins to move toward top dead center (TDC).
When air in the cylinder bore reaches a pressure greater
than that of the system pressure the discharge reed valves
open and air flows into the discharge line and air brake sys-
tem.
Air, during the compression stroke, flows into the hollow
center of the unloader piston through an opening in the end
of the piston. Compressed air acts on the interior surfaces
2
SUPPLY RESERVOIR
GOVERNOR
PORT
AIR INLET
PORT
AIR
DISCHARGE
PORT
VALVE
PLATE
INLET
VALVE
OPEN
PISTON MOVING DOWN
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
of the unloader piston and, along with the unloader piston
spring, holds the unloader piston against its seat on the
valve plate. See figures 5 & 7.
AIR INLET
PORT
AIR
DISCHARGE
PORT
VALVE
PLATE
INLET
VALVE
CLOSED
PISTON MOVING UP
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
NON-COMPRESSION OF AIR (UNLOADED)
When air pressure in the supply reservoir reaches the cut-
out setting of the governor, the governor delivers system
air to the compressor unloader port. Air entering the un-
loader port acts on the unloader piston causing it to move
away from its seat on the valve plate assembly. When the
DISCHARGE
VALVE
UNLOADER
CLOSED
PORT
UNLOADER
PISTON
DOWN &
SEATED
DISCHARGE
UNLOADER
VALVE
PORT
OPEN
UNLOADER
PISTON
DOWN &
SEATED