Bendix Commercial Vehicle Systems AD-IP INTEGRAL PURGE AIR DRYER 5/07 - Manual (Page 3)

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FIGURE 4 - AD-IP ™ INTEGRAL PURGE AIR DRYER CHARGE CYCLE
Air, along with the remaining water vapor, is further cooled
as it exits the oil separator and continues to flow upward
between the outer and inner shells. Upon reaching the top
of the cartridge the air reverses its direction of flow and enters
the desiccant drying bed. Air flowing down through the column
of desiccant becomes progressively drier as water vapor
adheres to the desiccant material in a process known as
“ADSORPTION.” The desiccant cartridge using the
adsorption process typically removes most of the water vapor
from the pressurized air.
Dry air exits the bottom of the desiccant cartridge and flows
through the center of the bolt used to secure the cartridge to
the end cover. Air flows down the center of the desiccant
cartridge bolt, through a cross drilled passage and exits the
air dryer delivery port through the 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 7.
Dry air flowing through the center of the desiccant cartridge
bolt also flows out the cross drilled purge orifice and into the
purge volume.
The air dryer will remain in the charge cycle until the air
brake system pressure builds to the governor cutout setting.
PURGE CYCLE (refer to Figure 5)
As air brake system pressure reaches the cutout 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 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 cutoff valve to close off the
supply of air from the compressor (this will be further
discussed in the Turbo Cutoff 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 initial purge and 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.
DESICCANT
BED
DELIVERY
CHECK VALVE
(OLD STYLE
SHOWN)
PURGE
VOLUME
DISCHARGE
PORT EXHAUST
PURGE
VALVE TURBO
CUTOFF
VALVE
ENGINE
TURBO
COMPRESSOR
GOVERNOR
PURGE
CONTROL
LINE
CONTROL
PORT
SUPPLY
PORT
OIL
SEPARATOR
PURGE
ORIFICE