Bendix Commercial Vehicle Systems AD-IS AIR DRYER AND RESERVOIR SYSTM - Manual (Page 5)

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Similarly, the governor also supplies air pressure to the
air dryer. The pressure also moves the air dryer purge
piston down, opening the purge valve to atmosphere and
closing off the compressor air supply to the turbo cut-off
valve (covered in the Turbo Cut-off Feature section of
this document). Water and contaminants captured are
expelled immediately when the purge valve opens. In
addition, air—which was flowing through the desiccant
cartridge—changes direction and begins to flow toward
the open purge valve. Contaminants collected by the air
dryer are removed by air flowing from the purge reservoir
through the desiccant drying bed to the open purge valve.
The initial purge and desiccant cartridge decompression
lasts only a few seconds, evidenced by an audible burst
of air at the air dryer exhaust.
FIGURE 3 - BENDIX ® AD-IS ® AIR DRYER AND RESERVOIR SYSTEM PURGE CYCLE
DIAGRAM SHOWS ALL PRESSURE
PROTECTION VALVES OPEN.
COMPRESSOR
GOVERNOR
DESICCANT
BED
DELIVERY
CHECK VALVE
(CLOSED)
PRIMARY
PORT (PRI)
PURGE VALVE
(OPEN)
TURBO
CUT-OFF
VALVE
(CLOSED) ENGINE
TURBO
UNLOADER
PORT
SUPPLY
PORT
PRIMARY
RESERVOIR
PRESSURE
PROTECTION
VALVES
AUXILIARY PORTS
(TO ACCESSORIES)
EXHAUST
SAFETY
VALVE PURGE
RESERVOIR
DRAIN VALVE
SECONDARY
RESERVOIR
SECONDARY
PORT (SEC)
PURGE
RESERVOIR
PURGE
ORIFICE
OIL COALESCING FILTER
(BENDIX ® AD-IS ® PURAGUARD ®
OIL COALESCING AIR DRYER)
A D C B
PURGE
CONTROL
CHANNEL
accessories. If the pressure protection valves are preset
to different values the valves will open—in order of lowest
setting to highest setting—when charging a flat system.
The air dryer and purge reservoir will remain in the charge
cycle until the air brake system pressure builds to the
governor cut-out setting of approximately 130 psi.
PURGE CYCLE (Refer to Figure 3.)
When air brake system pressure reaches the cut-out setting
of the governor, the governor unloads the compressor
activating the purge cycle of the air dryer and reservoir.
The governor unloads the compressor by allowing air
pressure to fill the line leading to the compressor unloader
mechanism. This suspends the delivery of compressed
air to the Bendix ® AD-IS ® air dryer and reservoir system.