Bendix Commercial Vehicle Systems DURAFLO 596 COMPRESSOR 10/04 - Manual (Page 3)

3
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
AIR INTAKE (LOADED)
The piston strokes are 180 degrees opposed. As one piston
is on an up stroke the opposing piston is on a down stroke.
During the piston down stroke, a vacuum is created in the
cylinder and ESS chamber within the cylinder head. The
vacuum causes the inlet check valve and sliding inlet valve
to flex open. Atmospheric air flows through the open inlet
check valve into and through the ESS chamber to the slid-
ing inlet valve. Air flowing past the sliding inlet valve fills the
cylinder above the piston. See Figures 4 & 7.
AIR COMPRESSION (LOADED)
When the piston reaches approximately bottom dead cen-
ter (BDC) the inlet check valve and sliding inlet valve close.
Air above the piston is trapped by the closed inlet 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 valves open and air flows into the
discharge line and air brake system.
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 control port of the synchro valve. The synchro
valve opens in response to control pressure from the gov-
ernor and delivers system pressure to either of the two
compressor unloader ports. Air entering the unloader port
acts on one unloader plunger directly and is simultaneously
conducted through a passage in the valve body assembly
to the other unloader plunger.
The unloader plungers move horizontally in their bores in
response to control pressure from the governor and syn-
chro valve. A guide pin in the unloader plunger rotates the
pivot arm which causes the inlet valve to slide. As the
inlet valve slides from the loaded to the unloaded position
it blocks the two discharge ports and opens the six inlet
ports connecting the cylinder bore to the ESS chamber.
When the piston travels upward, air in the cylinder is
trapped between the top of the piston and the closed inlet
check valve and is compressed. The intake check valves
prevent the intake air from escaping through the air intake
port when the compressor is in the unloaded ESS mode.
See Figures 5 & 7. PISTON
MOVING
DOWN
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
PISTON
MOVING
UP
The added volume of the ESS chamber lowers the amount
of compression. Air that is compressed during the upward
movement of the piston provides a driving force for the pis-
ton during its downward movement. As one piston is moving
downward the opposing piston is moving up. With the ex-
ception of losses in the form of heat, which is formed during
compression, the energy used to compress the air will be
reused as the driving force for the downward stroke of the
piston. This results in the compressor using very little power
in its unloading position. See Figures 6 & 7.
AIR
INLET
PORT
INLET
VALVE
OPEN
AIR
DISCHARGE
PORT
DISCHARGE
VALVE
CLOSED
UNLOADER
PISTON
INLET CHECK
VALVE OPEN
ESS
CHAMBER
AIR
DISCHARGE
PORT
INLET
VALVE
CLOSED
AIR
INLET
PORT
DISCHARGE
VALVE
OPEN
UNLOADER
PISTON
INLET CHECK
VALVE CLOSED
ESS
CHAMBER
FIGURE 6 - OPERATIONAL-UNLOADED
PISTON MOVING
UP & DOWN
INLET CHECK
VALVE CLOSED AIR
INLET
PORT
INLET
VALVE
OPEN
AIR
DISCHARGE
PORT
DISCHARGE
VALVE
CLOSED
UNLOADER
PISTON & PIVOT
ARM SLIDES INLET
VALVE OVER
ESS
CHAMBER