Bendix Commercial Vehicle Systems BA-921 COMPRESSOR_STD/CLOSED ROOM - Manual (Page 3)

3
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 (in naturally
aspirated applications) or pressurized air (in turbocharged
applications) fl ows through the open inlet valve and fi lls the
cylinder bore above the piston. See Figure 7A.
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.
At the same time air fl ows into the hollow center of the
unloader piston through an opening in the end of the piston.
Compressed air acts on the interior surfaces of the unloader
piston and, along with the unloader piston spring, holds the
unloader piston in the down position, against its seat on
the valve plate. See Figure 7B.
FIGURE 6 - STANDARD AND CLOSED ROOM BA-921 ®
COMPRESSOR CHARGING SYSTEMS
Compressor
Supply Reservoir
Governor
Reservoir
Port
Governor
Unloader Port
Air Dryer
Standard Compressors use an Inlet Check Valve
(ICV), or alternately, an ICV plus a reservoir,
in the air inlet line depending on the application
Compressor
Supply Reservoir
Governor
Reservoir
Port
Governor
Unloader Port
Air Dryer
Closed Room Compressor Typical System
FIGURE 7B - OPERATION - LOADED (COMPRESSION)
(SIMILAR FOR ALL COMPRESSORS - STANDARD
COMPRESSOR SHOWN)
Piston Moving Up
Air Inlet
Port
Inlet
Valve
Closed
Air
Discharge
Port
Discharge
Valve
Open
Unloader
Piston
Down &
Seated
Valve
Plate
Unloader
Port
Cooling
Plate
FIGURE 7A - OPERATION - LOADED (INTAKE). (SIMILAR
FOR ALL COMPRESSORS - STANDARD COMPRESSOR
SHOWN)
Piston Moving Down
Air Inlet
Port
Inlet
Valve
Open
Air
Discharge
Port
Discharge
Valve
Closed
Unloader
Piston
Down &
Seated
Valve
Plate
Unloader
Port
Cooling
Plate