Bendix Commercial Vehicle Systems AD-RP PuraGuard Oil Coalescing Remote Purge Air Dryers - Manual (Page 4)

4
cartridge, located between the outer and inner shells of the
cartridge — removes water in liquid form, as well as liquid
oil and solid contaminants.
After exiting the oil separator, air enters the space between
the desiccant drying bed and the outer cartridge shell
and fl ows down through the column of desiccant. Flowing
through the desiccant column, air becomes progressively
more dry as water vapor adheres to the desiccant
material in a process known as “ADSORPTION.” Using
the adsorption process, the desiccant cartridge typically
removes 95% of the water vapor from the pressurized air.
Dry air exits the bottom of the desiccant cartridge through
its center opening and returns to the air dryer body
assembly. The air then fl ows through the delivery check
valve assembly and out the delivery port to the fi rst (supply)
reservoir of the air system.
The air dryer will remain in the charge cycle until the
air brake system pressure builds to the governor cut-
out setting. To protect against over pressurization
of the Bendix
® AD-RP ™ air dryer, the purge valve
incorporates an integral relief valve feature. In the event
that the compressor unloader mechanism or governor
malfunctions, at approximately 200 psi — supply air
pressure, the AD-RP air dryer purge valve will open
(without control pressure) and vent excess air pressure
to atmosphere. (Refer to Figure 4)
PURGE CYCLE (Refer to Figure 5)
When air brake system pressure reaches the cut-out setting
of the governor — typically 130 psi — the compressor
unloads (air compression is stopped) and the purge cycle
of the air dryer begins. When the governor unloads the
compressor, it pressurizes both the compressor unloader
mechanism and the line connecting the governor unloader
port to the control port of the AD-RP air dryer body. Air
entering the control port is simultaneously directed to the
turbo cut-off valve and the purge valve control piston.
The initial purge cycle consists of two simultaneous
occurrences: (a) the closing of the turbo cut-off valve; and
(b) the opening of the purge valve. Each is discussed below
under a separate subheading.
DESICCANT
DELIVERY
CHECK
VALVE
DELIVERY
PORT
TURBO
CUT-OFF
CONTROL
PORT
GOVERNOR
COMPRESSOR
PURGE
VALVE
FRONT
RESERVOIR
REAR
RESERVOIR
ENGINE
TURBO
EXHAUST
PORT
SUPPLY
PORT
OIL
COALESCING
FILTER
PURGE
ORIFICE
SAFETY
VALVE
REMOTE
PURGE
PORT
REMOTE
PURGE
RESERVOIR
PURGE
CONTROL LINE
FIGURE 4 - BENDIX ® AD-RP ™ AIR DRYER SYSTEM - RELIEF VALVE OPERATION