Bendix Commercial Vehicle Systems AD-RP PuraGuard Oil Coalescing Remote Purge Air Dryers - Manual (Page 5)

5
TURBO CUT-OFF VALVE (Refer to Figure 5)
The primary function of the turbo cut-off valve is to
prevent loss of engine turbocharger air pressure
through the Bendix
® AD-RP ™ air dryer in systems
where the compressor intake is connected to the engine
turbocharger. The turbo cut-off valve also eliminates the
“puffi ng” of air out the open air dryer exhaust when a
naturally aspirated, single cylinder compressor is equipped
with an inlet check valve. Governor unloader pressure
causes the turbo cut-off valve piston to move and close.
With the turbo cut-off valve piston seated (closed position),
air in the discharge line and AD-RP air dryer inlet port is
prevented from entering the air dryer.
PURGE PISTON
The Bendix ® AD-RP ™ air dryer purge piston also moves in
response to governor unloader pressure, causing the purge
valve to open to atmosphere. Contaminants in the body
sump are instantly expelled when the purge valve opens.
Air — which was fl owing through the desiccant cartridge —
immediately changes direction and begins to fl ow back toward
the open purge valve. Oil and solid contaminants collected by
the oil separator are removed by air fl owing from the desiccant
drying bed to the open purge valve.
DESICCANT RE-ACTIVATION (DRYING THE
DESICCANT)
The initial decompression of the air dryer assembly lasts
only a few seconds and is evidenced by an audible burst of
air at the AD-RP air dryer exhaust. The actual reactivation
of the desiccant drying bed begins as dry air fl ows from
the purge volume through the purge orifi ce in the body
and into the desiccant bed. Pressurized air from the
purge volume expands after passing through the purge
orifi ce; its pressure is lowered and its volume increased.
The fl ow of dry air through the drying bed reactivates the
desiccant material by removing the water vapor adhering
to it. Generally 30 seconds minimum are required for the
entire purge volume of a standard AD-RP air dryer to fl ow
through the desiccant drying bed.
The delivery check valve assembly prevents air in the brake
system from returning to the air dryer during the purge
cycle. After the purge cycle is complete, the desiccant
has been reactivated (or dried), and the air dryer is ready
for the next charge cycle to begin. However, the purge
valve will remain open and will not close until air brake
system pressure is reduced and the governor signals the
compressor to charge the system.
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 5 - BENDIX ® AD-RP ™ AIR DRYER SYSTEM - PURGE CYCLE