Bendix Commercial Vehicle Systems 720CC COMPRESSOR - Manual (Page 3)

3
OPERATION
The compressor is driven by the vehicle's engine, and
functions continuously while the engine is in operation.
Actual compression of air is controlled by a downstream
component – like a discharge line unloader valve or an air
dryer without turbo cut-off valve – operating in conjunction
with a governor.
AIR INTAKE (LOADED)
Just as the piston begins the down stroke, (a position known
as top dead center, or TDC), the vacuum created in the
cylinder bore above the piston causes the inlet reed valve to
fl ex open. Atmospheric air fl ows through the open inlet valve
and fi lls the cylinder bore above the piston. See Figure 4.
AIR COMPRESSION (LOADED)
When the piston reaches the bottom of the stroke, (a
position known as bottom dead center, or BDC), the inlet
reed valve closes. Air above the piston is trapped by the
closed inlet reed valve and is compressed as the piston
moves upwards. When air in the cylinder bore reaches
a pressure greater than that of the system pressure, the
discharge reed valves open and allow air to fl ow into the
discharge line and air brake system. See Figure 5.
FIGURE 6 - TYPICAL BENDIX ® 720 CC (DLU) TWIN CYLINDER COMPRESSOR AIR CHARGING SYSTEM
21
22
S
D
S
C
UNL
Compressor
Governor
Air Dryer
Front Service
Reservoir
Rear Service
Reservoir
DLU Valve
FIGURE 5 - OPERATION - COMPRESSION
Piston Moving Up
Air Inlet
Port
Inlet
Valve
Closed
Air
Discharge
Port
Discharge
Valve
Open
Valve
Plate
Cooling
Plate
FIGURE 4 - OPERATION - INTAKE
Piston Moving Down
Air Inlet
Port
Inlet
Valve
Open
Air
Discharge
Port
Discharge
Valve
Closed
Valve
Plate
Cooling
Plate