SD-08-2415A

SB-10054530-4345

Bendix® AD-RP™ Remote Purge & AD-RP™ Puraguard® Oil Coalescing
Remote Purge Air Dryers
MEDALLION
(INDICATES BENDIX®
PURAGUARD® OIL
COALESCING CARTRIDGE)

“SPIN OFF”
DESICCANT
CARTRIDGE

MOUNTING
HOLES (3)

REMOTE
PURGE
PORT
PT 22
(NOT
MARKED)

CONTROL
PORT
CON 4
HEATER &
THERMOSTAT
CONNECTOR

SUPPLY
PORT
SUP 1

TURBO
CUT-OFF VALVE

DELIVERY PORT
DEL 2

EXHAUST PORT
FIGURE 1 - BENDIX® AD-RP™ REMOTE PURGE AIR DRYER

DESCRIPTION
The function of the Bendix® AD-RP™ remote purge air dryer
and AD-RP™ remote purge air dryer with PuraGuard® oil
coalescing technology is to collect and remove air system
contaminants in solid, liquid, and vapor form before they
enter the brake system. It provides clean, dry air to the
components of the brake system which increases the life of
the system and reduces maintenance costs. Daily manual
draining of the reservoirs is eliminated.
The Bendix AD-RP PuraGuard oil coalescing air dryer
has an identical appearance to the standard AD-RP air
dryer, but contains a coalescing media at the inlet of the
desiccant bed. The coalescing media provides a higher
level of oil removal over the standard AD-RP unit. The
AD-RP PuraGuard oil coalescing air dryer has all of the
same functions as the standard AD-RP air dryer and is
used in applications where lower oil concentration levels
are required.

IMPORTANT! When servicing, note that standard
AD-RP air dryers or air dryer cartridges may be
serviced with PuraGuard oil coalescing air dryers or
cartridges. The PuraGuard oil coalescing air dryers or
cartridges, however, must only be serviced with like
replacements.
Note: Unless otherwise stated in this manual, AD-RP
air dryer refers to both the standard and PuraGuard oil
coalescing remote purge air dryers.
The remote purge designation is used because the
AD-RP air dryer uses a small air volume, separate
from the air brake system, to perform the purge or
regenerative function.
The AD-RP air dryer consists of two major component
groups—a spin on desiccant cartridge assembly, and a
die cast aluminum body assembly. The desiccant cartridge
is self-contained and serviced as a complete assembly.
1

GENERAL SAFETY GUIDELINES
WARNING! PLEASE READ AND FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following guidelines should be observed AT ALL TIMES:
▲ Park the vehicle on a level surface, apply the
parking brakes and always block the wheels.
Always wear personal protection equipment.
▲ Stop the engine and remove the ignition key
when working under or around the vehicle.
When working in the engine compartment,
the engine should be shut off and the ignition
key should be removed. Where circumstances
require that the engine be in operation, EXTREME
CAUTION should be used to prevent personal
injury resulting from contact with moving,
rotating, leaking, heated or electrically-charged
components.
▲ Do not attempt to install, remove, disassemble
or assemble a component until you have read,
and thoroughly understand, the recommended
procedures. Use only the proper tools and
observe all precautions pertaining to use of those
tools.
▲ If the work is being performed on the vehicle’s
air brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure
from all reservoirs before beginning ANY work
on the vehicle. If the vehicle is equipped with a
Bendix® AD-IS® air dryer system, a Bendix® DRM™
dryer reservoir module, or a Bendix® AD-9si™ air
dryer, be sure to drain the purge reservoir.
▲ F o l l o w i n g t h e v e h i c l e m a n u f a c t u r e r ’s
recommended procedures, deactivate the
electrical system in a manner that safely removes
all electrical power from the vehicle.

▲ Never exceed manufacturer’s recommended
pressures.
▲ Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove
a component or plug unless you are certain all
system pressure has been depleted.
▲ Use only genuine Bendix ® brand replacement
parts, components and kits. Replacement
hardware, tubing, hose, fittings, etc. must be of
equivalent size, type and strength as original
equipment and be designed specifically for such
applications and systems.
▲ Components with stripped threads or damaged
parts should be replaced rather than repaired.
Do not attempt repairs requiring machining or
welding unless specifically stated and approved
by the vehicle and component manufacturer.
▲ Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
▲ For vehicles with Automatic Traction Control
(ATC), the ATC function must be disabled (ATC
indicator lamp should be ON) prior to performing
any vehicle maintenance where one or more
wheels on a drive axle are lifted off the ground
and moving.
▲ The power MUST be temporarily disconnected
from the radar sensor whenever any tests USING
A DYNAMOMETER are conducted on a Bendix®
Wingman® Advanced™-equipped vehicle.

▲ You should consult the vehicle manufacturer's operating and service manuals, and any related literature,
in conjunction with the Guidelines above.

BENDIX® AD-RP™
AIR DRYER

GOVERNOR

COMPRESSOR

FIGURE 2 - BENDIX® AD-RP™ AIR DRYER SYSTEM DRAWING
2

REMOTE PURGE
RESERVOIR

DESICCANT
OIL
COALESCING
FILTER
PURGE
ORIFICE

REMOTE
PURGE
RESERVOIR

DELIVERY
CHECK
VALVE

REMOTE
PURGE
PORT

CONTROL
PORT
PURGE
CONTROL LINE

REAR
RESERVOIR

FRONT
RESERVOIR

SUPPLY
PORT

GOVERNOR

ENGINE
TURBO

TURBO
CUT-OFF

SAFETY
VALVE

EXHAUST
PORT

DELIVERY
PORT
PURGE
VALVE

COMPRESSOR
FIGURE 3 - BENDIX® AD-RP™ AIR DRYER SYSTEM - CHARGE CYCLE

The aluminum body of the Bendix® AD-RP™ air dryer
contains these serviceable components or assemblies:
the turbocharger cut-off valve; the heater and thermostat
assembly; a delivery check valve assembly; and the
combined purge and relief valve assembly. All service
and replacement can be accomplished from the exterior
of the dryer without removal from the vehicle. The spin-on
desiccant cartridge is removed and installed using a “strap
wrench.”
The AD-RP air dryer has four female pipe thread air
connections identified as follows: (Also refer to Figure 1.)

Air Connection Port ID Function/Connection
CON 4

Control Port (purge valve control
& turbo cut-off)

SUP 1

Supply Port (air in)

DEL 2

Delivery Port (air out)

PT 22
(not identified on
the air dryer)

Remote Purge Port

OPERATION
GENERAL
The AD-RP air dryer alternates between two operational
modes or “cycles” during operation: the Charge Cycle and
the Purge Cycle. What follows is a description of operation
separated into these “cycles”.

CHARGE CYCLE (Refer to Figure 3.)
When the compressor is loaded (compressing air)
compressed air, along with oil, oil vapor, water and water
vapor flows through the compressor discharge line to the
supply port of the air dryer body. Air entering the supply
port immediately encounters the “turbo cut-off” valve. With
no air pressure in the control port, the turbo cut-off piston
moves the valve away from its seat in the body, allowing
the supply air to enter the body. As air travels through the
end cover assembly, its direction of flow changes several
times, reducing the temperature, causing contaminants
to condense and drop to the bottom (or sump) of the air
dryer body. After exiting the end cover, the air flows into the
desiccant cartridge where an oil separator — or coalescing
filter, if equipped with a Bendix® PuraGuard® oil coalescing
3

DESICCANT
OIL
COALESCING
FILTER

REMOTE
PURGE
RESERVOIR

PURGE
ORIFICE

DELIVERY
CHECK
VALVE

REMOTE
PURGE
PORT

CONTROL
PORT
PURGE
CONTROL LINE

REAR
RESERVOIR

FRONT
RESERVOIR

SUPPLY
PORT

GOVERNOR

ENGINE
TURBO

TURBO
CUT-OFF
EXHAUST
PORT

SAFETY
VALVE

DELIVERY
PORT
PURGE
VALVE

COMPRESSOR

FIGURE 4 - BENDIX® AD-RP™ AIR DRYER SYSTEM - RELIEF VALVE OPERATION

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 flows 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 flows through the delivery check
valve assembly and out the delivery port to the first (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 cutout 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

4

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
OIL
COALESCING
FILTER

REMOTE
PURGE
RESERVOIR

PURGE
ORIFICE

DELIVERY
CHECK
VALVE

REMOTE
PURGE
PORT

REAR
RESERVOIR

CONTROL
PORT
PURGE
CONTROL LINE

FRONT
RESERVOIR

SUPPLY
PORT

GOVERNOR

ENGINE
TURBO

DELIVERY
TURBO
SAFETY
PORT
CUT-OFF
VALVE
EXHAUST
PURGE
PORT
VALVE

COMPRESSOR

FIGURE 5 - BENDIX® AD-RP™ AIR DRYER SYSTEM - PURGE CYCLE

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 AD-RP air dryer in systems where the compressor
intake is connected to the engine turbocharger. The turbo
cut-off valve also eliminates the “puffing” 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 flowing through the desiccant cartridge —
immediately changes direction and begins to flow back toward
the open purge valve. Oil and solid contaminants collected by
the oil separator are removed by air flowing 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 flows from
the purge volume through the purge orifice in the body
and into the desiccant bed. Pressurized air from the
purge volume expands after passing through the purge
orifice; its pressure is lowered and its volume increased.
The flow 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 flow
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. 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.
5

PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended
warranty may be voided if intrusive maintenance is
performed during this period. Because no two vehicles
operate under identical conditions, maintenance and
maintenance intervals will vary. Experience is a valuable
guide in determining the best maintenance interval for any
one particular operation.
Every 900 operating hours, or 25,000 miles or three
(3) months:
1. Check for moisture in the air brake system by opening
reservoirs, drain cocks or drain valves and checking
for the presence of water. If moisture is present,
the desiccant cartridge may require replacement;
however, the following conditions can also cause
water accumulation and should be considered before
replacing the desiccant:
A. An outside air source has been used to charge the
system. This air does not pass through the drying
bed.
B. Air usage is exceptionally high and not normal for
a highway vehicle. This may be due to accessory
air demands or some unusual air requirement that
does not allow the compressor to load and unload
(compressing and non-compressing cycle) in a
normal fashion. Check for high air system leakage.
If the vehicle vocation has changed, it may be
necessary to upgrade the compressor size. Refer
to Appendix A / Table A in this document . View the
column titled Vehicle Vocation.
C. The air dryer has been installed in a system that
has been previously used without an air dryer. The
system will be saturated with moisture and several
weeks of operation may be required to dry it out.

3. Check mounting bolts for tightness. Re-torque to
50 lb-ft.
4. Perform the Operation & Leakage Tests listed in this
publication.
Every 3,600 operating hours, or 100,000 miles or twelve
(12) months:
1. Test the AD-RP air dryer turbo cut-off and purge valves
for leakage. Disconnect the supply, control and delivery
lines from the AD-RP dryer. Perform the tests below in
the order they are presented.
A. Apply 120 psi shop air pressure to the control port
and a soap solution to the supply port. If leakage
exceeds a one (1) inch bubble in five (5) seconds,
repair the turbo cut-off piston and valve before
proceeding to step 2.
B. With 120 psi shop air pressure applied to the control
port, apply a soap solution to the purge exhaust port.
If leakage exceeds a one (1) inch bubble in five (5)
seconds, repair the purge piston and valve before
proceeding to step 2.
C. With 120 psi shop air pressure applied to the control
and supply port, apply a soap solution to the purge
exhaust port. If leakage exceeds a one (1) inch
bubble in five (5) seconds, repair the turbo cut-off
piston and valve before proceeding to step 2.
D. With a plug installed in the delivery port, 0 psi in the
control port, and 120 psi applied to the supply port,
apply a soap solution to the purge exhaust port. If
leakage exceeds a one (1) inch bubble in five (5)
seconds, repair the purge piston and valve before
proceeding to step 2.

D. Location of the air dryer is too close to the air
compressor. Refer to Locating the Bendix® AD-RP™
Air Dryer On Vehicle section, plus Appendix A /
Table A, column 2 for discharge line length.

2. Perform the Operation & Leakage Tests shown in this
publication.

E. In areas where more than a 30 degree range of
temperature occurs in one day, small amounts
of water can temporarily accumulate in the air
brake system due to condensation. Under these
conditions, the presence of small amounts of
moisture is normal and should not be considered
as an indication that the dryer is not performing
properly.

1. Replace the air dryer desiccant cartridge.

Note: A small amount of oil in the system is normal and
should not be considered as a reason to replace the
desiccant cartridge; oil-stained desiccant can function
adequately.

6

2. Visually check for physical damage to the AD-RP™ air
dryer such as a dented desiccant cartridge, chafed or
broken air and electrical lines, and broken or missing
parts.

Every 10,800 hours; or 350,000 miles or 36 months:
Note: The desiccant change interval may vary from vehicle
to vehicle. Although typical desiccant cartridge life is three
years, many will perform adequately for a longer period of
time. In order to take maximum advantage of desiccant life
and assure that replacement occurs only when necessary,
it is important that you perform the Operation & Leakage
Tests.
2. Perform the Operation & Leakage Tests shown in this
publication.

For Bendix® AD-RP™ PuraGuard® oil coalescing air
dryers only: Preventive Maintenance is as easy as 1-2-3

noted, tighten the cartridge using a strap wrench and
re-test for leakage.