Bendix Commercial Vehicle Systems AD-SP SYSTEM PURGE AIR DRYER 10/04 - Manual (Page 5)

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FIGURE 3 - BENDIX ® AD-IP ® INTEGRAL PURGE AIR DRYER PURGE CYCLE
DESICCANT
BED
PURGE
VOLUME
DISCHARGE
PORT
EXHAUST
PURGE
VALVE
TURBO
CUT-OFF VALVE
ENGINE
TURBO
COMPRESSOR
GOVERNOR
PURGE
CONTROL
LINE
CONTROL
PORT
SUPPLY
PORT
OIL
SEPARATOR
PURGE
ORIFICE
DELIVERY
CHECK VALVE
Note: the early end cover designs incorporated a vertical
delivery check valve while the newer versions have a
horizontal check valve. Both have the same function, but
the components are not interchangeable. See Figure 4.
A small amount of the air flowing through the center of the
desiccant cartridge bolt flows out the cross drilled purge
orifice and into the purge volume, for regenerating the
desiccant. The air dryer will remain in the charge cycle
until the air brake system pressure builds to the governor
cut-out setting.
PURGE CYCLE (Refer to Figure 3)
As air brake system pressure reaches the cut-out setting
of the governor, the governor unloads the compressor (air
compression is stopped) and the purge cycle of the air
dryer begins. When the governor unloads the compressor,
it pressurizes the compressor unloader mechanism and the
line connecting the governor unloader port to the Bendix ®
AD-IP ® air dryer end cover control port. The purge piston
moves in response to air pressure causing the purge
valve to open to the atmosphere and the turbo cut-off
valve to close off the supply of air from the compressor
(this will be further discussed in the Turbo Cut-off Feature
section). Water and contaminants in the end cover sump
are expelled immediately when the purge valve opens.
Also, air which was flowing through the desiccant cartridge
changes direction and begins to flow toward the open purge
valve. Liquid oil and solid contaminants collected by the oil
separator are removed by air flowing from the purge volume
through the desiccant drying bed to the open purge valve.
The desiccant cartridge decompression lasts only a few
seconds and is evidenced by an audible burst of air at the
AD-IP air dryer exhaust. No purging of air should occur
after 30 seconds.