Bendix Sd 08 2415A Users Manual 2415A_US_001

2015-04-02

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SD-08-2415A

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 the 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. The dryer 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

REAR
RESERVOIR

CONTROL
PORT
PURGE
CONTROL LINE

FRONT
RESERVOIR

SUPPLY
PORT

GOVERNOR

ENGINE
TURBO

TURBO
CUT-OFF

DELIVERY
PORT

SAFETY
VALVE

PURGE
VALVE

EXHAUST
PORT

COMPRESSOR

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

The aluminum body of the Bendix® AD-RP™ air dryer
contains the following 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 removing it 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

REAR
RESERVOIR

CONTROL
PORT
PURGE
CONTROL LINE

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

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

TURBO
CUT-OFF

SAFETY
VALVE

EXHAUST
PORT

DELIVERY
PORT
PURGE
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 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
“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), 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.
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 every 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. See 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.
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.
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.
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.

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.
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 every 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.
2. Perform the Operation & Leakage Tests shown in this
publication.
Every 10,800 hours; or every 350,000 miles or 36
months:
1. Replace the air dryer desiccant cartridge.
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 ensure 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
Adhering to a preventive maintenance schedule is
crucial to keeping a vehicle’s air system clean and to
help ensure superior performance of all components that
utilize system air — such as brakes, emissions equipment
and automated manual transmissions. Depending on
vocation, Bendix recommends a 1, 2 or 3-year air dryer
cartridge replacement on vehicles equipped with a Bendix®
compressor.
For severe service application — such as residential refuse
trucks or school buses — the air dryer cartridge should be
replaced every year or every 100,000 miles. For pick-up
and delivery operations, or for double- and triple-trailer
line haul trucks, replacement is recommended every two
years or 200,000 miles. Line-haul operations using a single
trailer should swap the ﬁlter out every three (3) years or
300,000 miles. The recommended intervals for trucks
equipped with non-Bendix compressors are 6 months
(50,000 miles), one year (100,000 miles), and two years
(200,000 miles), respectively.
More frequent intervals may be required depending
on a vehicle’s age, its compressor condition, use of a
non-Bendix compressor, the operating environment, the
vehicle’s vocation, and its usage. In conjunction with these
guidelines, ﬂeets can determine the functionality of their
ﬁlters by checking for moisture in the air brake system
monthly. If moisture is present, the air dryer cartridge may
require replacement. Refer to the Bendix Service Data
Sheet of the speciﬁc air dryer for additional information.

This air dryer is intended to remove moisture and other
contaminants normally found in the air brake system.
Do not inject alcohol, anti-freeze, or other de-icing
substances into or upstream of the air dryer. Alcohol
is removed by the dryer, but reduces the effectiveness
of the device to dry air. Use of other substances can
damage the air dryer and may void the warranty.

OPERATION & LEAKAGE TESTS (ALSO SEE
VIDEO BW2327*)
1. Check for excessive leakage around the purge valve.
With the compressor in the loaded mode (compressing
air), apply a soap solution to the purge valve exhaust
port and observe that leakage does not exceed a
one (1) inch bubble in ﬁve (5) seconds. If the leakage
exceeds the maximum speciﬁed, service the purge
valve assembly.
2. Check for leakage around the desiccant cartridge. With
the compressor in loaded mode (compressing air),
apply a soap solution around the desiccant cartridge

seal and observe that no leakage occurs. If leakage is
noted, tighten the cartridge using a strap wrench and
re-test for leakage.
3. While observing the dash gauge(s), build up system
pressure at approximately 1,800 engine/compressor
rpm to governor cut-out. Note the pressure on the
dash gauge(s) at the moment governor cut-out occurs
and that the Bendix® AD-RP™ air dryer purges with
an audible escape of air. Observe the dash gauge(s)
pressure for two minutes after the purge cycle begins.
The front axle service (secondary) and the rear axle
(primary) reservoir pressures should not drop more
than 2 psi below the governor cut-out pressure noted.
Perform this test three times to positively conﬁrm the
values. If the pressure drop in the reservoirs exceeds
2 psi, check the air brake system for excessive leakage
and repair.
Build up system pressure to governor cut-out, wait a
minimum of 30 seconds for the purge cycle to complete,
then apply and release the service brakes to reduce
system air pressure to governor cut-in. Note that the
system once again builds to full pressure and is followed
by an Bendix AD-RP air dryer purge.
4. Check the operation of the heater and thermostat
assembly in the body during cold weather operation
(if possible) as follows:
A. Electric Power to the Heater and Thermostat
With the ignition or engine kill switch in the ON
position, check for voltage to the heater and
thermostat assembly using a voltmeter or test light.
Unplug the electrical connector at the air dryer and
place the test leads on each of the pins of the male
connector. If there is no voltage, look for a blown
fuse, broken wires, or corrosion in the vehicle wiring
harness. Check to see if a good ground path exists.
B. Thermostat and Heater Operation
Turn off the ignition switch and cool the body
assembly to below 40° F.
Note: If this test is performed in warm weather (above
30° F) it may be necessary to remove the heater and
thermostat assembly and cool it in a freezer.
Using an ohmmeter, check the resistance between the
electrical pins in the connector. The resistance should be
1.5 to 1.7 ohms for the 12 volt heater assembly and 6.0 to
6.9 ohms for the 24 volt heater assembly. If the resistance
is higher than the maximum stated, replace the heater and
thermostat assembly.
Warm the heater and thermostat assembly to over 90°F and
once again check the resistance. The resistance should
exceed 1000 ohms. If the resistance values obtained are
within the stated limits, the thermostat and heater assembly
is operating properly. If the resistance values obtained are
outside the stated limits, replace the heater and thermostat
assembly.

* Available through the Bendix Marketing Center on www.bendix.com
7

DESICCANT
CARTRIDGE
CONTROL
PORT

CAP

REMOTE
PURGE PORT
AD-RP™ AIR
DRYER BODY

O-RINGS

RETAINING RING

DELIVERY PORT

RETAINING RING
SUPPLY PORT

HEATER &
THERMOSTAT
ASSEMBLY

PURGE VALVE

O-RING

CONNECTOR

O-RING

PISTON

PURGE PISTON
SPRING
EXHAUST COVER
RETAINING RING

FIGURE 6 - BENDIX® AD-RP™ REMOTE PURGE AIR DRYER EXPLODED VIEW

REPAIRING THE BENDIX® AD-RP™ AIR DRYER

BENDIX AD-RP AIR DRYER REMOVAL

GENERAL

1. Park the vehicle on a level surface and prevent
movement by means other than the brakes.

If — after completing the routine operation and leakage
tests — it has been determined that one or more
components of the air dryer requires replacement or
maintenance, refer to the list below to ﬁnd the appropriate
kit(s). When repairing or replacing components of the air
dryer use only genuine Bendix® parts.
Maintenance Kits Available
Part
Number

Kit

109495

12 Volt Replacement Heater & Thermostat
Assembly Kit

109496

24 Volt Replacement Heater & Thermostat
Assembly Kit

109993

Turbo Cut-Off Maintenance Kit

5008414

Standard Desiccant Cartridge
Replacement Kit

5008414PG

Bendix® PuraGuard® Desiccant Cartridge
Replacement Kit

109995

Purge & Relief Valve Maintenance Kit

5008972

Purge Volume Kit (uses 288 cu. in. reservoir
part no. 275816)

For a more complete listing of service parts refer to the
Bendix Quick Reference Catalog (BW1114).
8

2. Drain ALL reservoirs to 0 psi (0 kPa) Caution: The
compressor discharge line may still contain
residual pressure.
3. Identify, mark and disconnect the supply, delivery,
control, and remote purge port air lines. Disconnect
the wiring harness connector from the heater and
thermostat assembly connector on the body assembly.
4. If so equipped, disconnect, remove and save the
exhaust line from the exhaust port of the air dryer.
5. Remove the three mounting bolts that secure the air
dryer to the vehicle and remove the air dryer.
Note: It is important to retain the three mounting bolts
since their length is speciﬁc to mounting the air dryer
without damage. If these bolts must be replaced, the
same length must be used.
6. Remove the Bendix ® AD-RP™ air dryer from its
mounting brackets on the vehicle.

DISASSEMBLY FOR PART REPLACEMENT AND
KIT INSTALLATION
1. The following disassembly and assembly procedures
are presented for reference and assumes that the
appropriate Bendix® AD-RP™ air dryer kits are on hand.
The instructions provided with these parts and kits
should be followed instead of the instructions presented
here.
2. The replacement parts and maintenance kits that are
available do not require full disassembly and in most
cases do not require the removal of the AD-RP air dryer
from the vehicle.
3. If removal of the air dryer is necessary, adhere to the
following caution:

DISASSEMBLY - HEATER AND THERMOSTAT
1. Disconnect the vehicle wiring harness connector that
mates with the heater and thermostat connector on the
body. Pry the lock tabs on the vehicle wiring harness
connector out, before removal from the air dryer
connector. Make sure the connector seal is present
on the vehicle wiring harness connector.
2. Remove the retaining ring that secures the heater and
thermostat in the body.
3. Carefully pull the heater and thermostat assembly
straight out of the body.
4. Remove the o-ring from the heater connector.

DISASSEMBLY - DESICCANT CARTRIDGE

CAUTION: While performing service on the AD-RP air
dryer, it is not recommended that a clamping device (vise,
C-clamp, etc.) be used to hold any die cast aluminum
component as damage may result. To hold the body, install
a pipe nipple in the supply port and clamp the nipple into
a vise.

1. Place a strap wrench, or equivalent tool, on the
desiccant cartridge next to the lip low on the cartridge.
Rotate counterclockwise to remove the desiccant
cartridge.

DISASSEMBLY - TURBO CUT-OFF VALVE

1. Clean the exterior of the body.

1. Loosen the supply port line and allow any residual air
in the compressor discharge line to drain.

2. Using a clean rag, wipe the body bores clean.

2. Remove the retaining ring from the body assembly, then
remove the turbo cut-off cap from the body. Remove
the turbo cut-off cap o-ring.
3. Remove the turbo cut-off piston from the body.
4. Remove the large and small diameter o-rings from the
piston.

DISASSEMBLY - PURGE/RELIEF VALVE
1. If so equipped, disconnect, remove and save the
exhaust line from the exhaust port of the air dryer.
2. Remove the retaining ring from the body assembly, then
remove the non-metallic exhaust cover and spring from
the body. Note: The spring exerts a 30 pound force
against the exhaust cover.

CLEANING, INSPECTION AND ASSEMBLY
PREPARATION

3. Inspect for physical damage to the body casting, broken
and/or missing parts.
4. Inspect the interior and exterior of the body for severe
corrosion, pitting and cracks. Superﬁcial corrosion and/
or pitting on the exterior portion is acceptable.
5. Inspect the bores, valve seating and o-ring contact
areas for deep scufﬁng or gouges or nicks that would
not permit an air tight seal.
6. Inspect the pipe threads in the body. Make certain they
are clean and free of thread sealant.
7. Inspect the purge valve piston seat for nicks and
excessive wear.
8. Inspect all air line ﬁttings for corrosion. Clean all old
thread sealant from the pipe threads.

3. Carefully remove the purge piston from the body and
remove the o-ring from the purge piston.

9. All o-rings removed should be discarded and replaced
with new o-rings provided in the appropriate kit(s).

4. The purge valve has two different sides. Note which
side is visible before removing the valve. Remove the
valve from the body.

10. Lubricate the body bores and o-ring grooves, in the
body and components, with the grease supplied in the
Bendix® maintenance kits.
11. Lubricate all o-rings with the grease supplied in the
Bendix maintenance kits. Any component exhibiting a
condition described in steps 3 to 8 should be replaced.

ASSEMBLY - TURBO CUT-OFF VALVE
1. Lubricate all o-rings with the grease supplied in the
Bendix® maintenance kits.
2. Install the large and small diameter o-rings on the
piston.
3. Install the turbo cut-off piston assembly in the body.
4. Install the o-ring on the turbo cut-off cap then install the
cap in the body.
5. Install the retaining ring in the body, making certain that
it is fully seated in its groove.
6. Before placing vehicle back into service, perform the
Operation & Leakage Tests detailed in this manual.

ASSEMBLY - PURGE/RELIEF VALVE
1. Lubricate the piston o-ring with the grease supplied in
the Bendix maintenance kit. Also, lubricate completely
around the outside edge of the purge valve.
2. Install the purge valve in the body. Make certain that it is
ﬁrmly and squarely seated in the body with the correct
side visible. Note: The three (3) "bumps" on the purge
valve should not be visible. If the three (3) "bumps" are
visible after the purge valve is installed, the valve must
be removed and re-installed.
3. Install the o-ring on the purge piston, then install the
piston in the body taking care not to cut the piston
o-ring.
4. Install the non-metallic exhaust cover and spring in the
body.
5. Install the retaining ring in the groove in the body. Make
certain that it is fully seated in its groove.
6. If so equipped, reconnect the exhaust line from the
exhaust port of the air dryer.
7. Re-tighten the supply port line.
8. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.

ASSEMBLY - HEATER AND THERMOSTAT
1. Lubricate the connector o-ring with the grease supplied
in the Bendix maintenance kits.
2. Install the o-ring on the connector, then slide the heater
and thermostat assembly into the body making certain
not to cut the o-ring. Note that the "tab" on the assembly
ﬁts into the corresponding slot in the body.
3. Install the retaining ring in the groove in the body,
making certain that it is fully seated in its groove.
4. Apply a dielectric grease on the heater and thermostat
connector contacts (both the heater and thermostat and
vehicle wiring harness connector halves).

5. After making certain the accordion seal is in place on
the vehicle wire harness connector, connect the wire
harness to the heater and thermostat assembly on the
dryer until its lock tab snaps ("clicks") into place.
6. Before placing the vehicle back into service, perform
the Operation & Leakage Tests stated elsewhere in this
manual.

ASSEMBLY - DESICCANT CARTRIDGE
1. Lubricate the desiccant cartridge sealing ring with the
grease supplied in the Bendix maintenance kits and
replacement parts.
2. Screw the desiccant cartridge onto the body (by hand)
until the seal makes contact with the body. Rotate it
clockwise approximately one full turn. If necessary,
place a strap wrench or equivalent tool on the desiccant
cartridge next to the lip low on the cartridge.
Note: If the replacement cartridge is supplied with an
o-ring for the dryer threads, discard it. This o-ring is
not to be used.
IMPORTANT: If the cartridge removed was a Bendix®
PuraGuard® oil coalescing style cartridge, it must be
replaced with another PuraGuard-style cartridge.
3. Before placing vehicle back into service, perform the
Operation & Leakage Tests outlined in this manual.

INSTALLATION
1. Install the assembled Bendix® AD-RP™ air dryer back
onto the vehicle using the same three mounting bolts
retained during removal. Tighten, then torque the three
cap screws to 50 lb-ft.
2. Reconnect the four air lines to the proper ports on the
body (identiﬁed during disassembly). If the ﬁttings were
removed from the body, use a thread sealant making
certain none enters the body during re-installation.
3. Apply a dielectric grease on the heater and thermostat
connector contacts (both the heater and thermostat and
vehicle wiring harness connector halves).
4. After making certain the accordion seal is in place on
the vehicle wire harness connector, connect the wire
harness to the heater and thermostat assembly on the
dryer by plugging it into the air dryer connector until its
lock tab snaps ("clicks") into place.
5. If so equipped, reconnect the exhaust line to the
exhaust port of the air dryer.
6. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.

RETROFITTING THE BENDIX® AD-RP™ AIR
DRYER
GENERAL
The following retrofit instructions are presented for
reference purposes only. Bendix® replacement air dryers
are packaged with the most up-to-date installation
instructions. The instructions packaged with the Bendix®
AD-RP™ air dryer should be followed instead of those
presented here. The preceding portion of this manual
deals with "in-service" repair and/or replacement of
the AD-RP air dryer. This portion of the manual is
concerned with installing an AD-RP air dryer on a
vehicle not previously equipped with one.

VEHICLE APPLICATION REQUIREMENTS
The basic application requirements presented here apply
to a standard air dryer installation. The majority of highway
vehicles in use today will meet these basic requirements,
however some may not. Examples of vehicles that may
not meet the requirements include refuse trucks, city
coaches, bulk trailer unloading operations and other high
air consumption systems. While the AD-RP air dryer can be
used on these vehicles, the standard installation procedure
presented in this manual may require modiﬁcation to
ensure proper operation and service life. Consult your local
authorized Bendix parts outlet or sales representative for
additional information.
1. Charge Cycle Time - The AD-RP air dryer is designed
to provide clean, dry air for the brake system. When a
vehicle's air system is used to operate non-brake air
accessories it is necessary to determine that — during
normal, daily operation — the compressor should
recover from governor "cut-in" to governor "cut-out"
(usually 110 psi to 130 psi) in 90 seconds or less at
engine RPMs commensurate with the vehicle vocation.
Note: The Bendix AD-RP air dryer must be used in
conjunction with governors which have a 120 to 130 psi
nominal cut-out pressure. If a governor is used that is
not within this limitation, contact your Bendix parts outlet
or sales representative for additional information. If the
recovery time consistently exceeds this limit, it may be
necessary to "by-pass" the air accessory responsible
for the high air usage.

3. European Air Brake Systems - The AD-RP air dryer
must not be installed in brake systems that incorporate
compressors without integral unloading mechanisms
and/or utilize a compressor discharge line unloader
valve. When vehicles of this type are encountered,
other Bendix air dryer models must be used. Consult
your local authorized Bendix parts outlet or sales
representative for additional information.
4. Air Compressor Size - The AD-RP air dryer was
designed primarily for use with compressors rated up
to 30 CFM. Contact and authorized Bendix parts outlet
or a Bendix sales representative for assistance when
using the AD-RP dryer with a compressor which has a
rated displacement exceeding 30 CFM.
5. Holset "E or QE" Type Air Compressors - The AD-RP
dryer can be installed with the Holset Type "E or QE"
compressor. When the AD-RP air dryer is used in this
installation, the Holset ECON valve should be removed
and the special oriﬁce check valve in the "make-up" line
should be removed and replaced with a conventional
single check valve.
6. Use the following guidelines to determine the vehicle
application suitable for the Bendix AD-RP air dryer:

Total Vehicle
Reservoir Volume

Requirement

Less than
12,500 cu. in.

Bendix® AD-RP™ Air Dryer
(use kit part no. 5008972)

Greater than
12,500 cu. in.

Contact Bendix Commercial Vehicle
Systems LLC.

2. Purge Cycle Time - During normal vehicle operation, the
air compressor must remain unloaded for a minimum
of 30 seconds. This minimum purge time is required
to ensure complete regeneration of the desiccant
material. If the purge time is occasionally shorter than
the times speciﬁed, no permanent ill effect should be
expected. If the purge time is consistently less than
the minimum, however, an accessory by-pass system
must be installed.

VEHICLE PREPARATION

CONNECTING THE AIR LINES

1. Park the vehicle on a level surface and prevent
movement by means other than the brakes.

Important General Instructions

2. Drain all reservoirs to 0 psi (0kPa).

These instructions apply to all installations of the AD-RP
dryer regardless of whether the unit is replacing an existing
air dryer, or is being installed on a vehicle that never had
one installed. If the vehicle is currently equipped with an
air dryer some additional considerations apply.

LOCATING THE BENDIX® AD-RP™ AIR DRYER
ON VEHICLE
1. The Bendix ® AD-RP ™ air dryer must be mounted
vertically (purge exhaust port toward road surface)
outside the engine compartment in an area of air ﬂow
while the vehicle is in motion. The AD-RP air dryer must
not be exposed to direct wheel splash (note: locating
behind an axle mud ﬂap is acceptable).
2. Locate the AD-RP air dryer as close to the ﬁrst (supply)
reservoir as possible.
3. Do not locate the AD-RP air dryer near heat producing
components such as the vehicle exhaust, and make
certain adequate clearance from moving components
(e.g. drive shaft, suspension, pitman arm, etc.) is
provided.
4. Locate the Bendix AD-RP air dryer on the vehicle
so that a minimum of one (1) inch clearance above
the cartridge is available to allow cartridge servicing.
Additionally, provide access to the bracket bolts so the
unit may be removed when necessary.

A. If the AD-RP air dryer is replacing an integral purge
air dryer — such as the Bendix® AD-9® air dryer — on
a vehicle equipped with any compressor except the
Cummins-Holset type E & QE, all that is necessary
is that the air dryer be removed and the existing air
lines be correctly connected to the AD-RP dryer. An
additional purge volume (minimum 200 cubic inches)
must also be installed and connected to the AD-RP
Remote Purge Port. The extended Purge Volume Kit
5008972 can be used.
B. If the AD-RP air dryer is replacing an integral purge
air dryer — such as the Bendix® AD-4™ or AD-9 air
dryer — on a vehicle equipped with a Cummins-Holset
type E or QE compressor, in addition to removing the
existing air dryer and correctly connecting the existing
air lines to the AD-RP dryer, it will be necessary to
remove and discard the Holset ECON and special
oriﬁce check valve.

5. When choosing the mounting location for the AD-RP
dryer, note the discharge line length requirements
stated under the heading Connecting the Air Lines,
elsewhere in this manual.
Note: Under normal operating conditions, the maximum
inlet air temperature for the AD-RP dryer is 160° F.

MOUNTING THE BENDIX AD-RP AIR DRYER
1. Install the AD-RP air dryer by referring to Figure 7
and drilling the triangular mounting hole pattern in a
mounting plate and then mounting the plate on the
vehicle, or by drilling the mounting hole pattern in the
area of the vehicle chosen for mounting. Note: Check
the vehicle manual before drilling a frame member.
2. Important: The length of the three mounting bolts used
to attach the AD-RP air dryer to the mounting plate is
very important. Refer to Figure 8. The threaded end of
the 1/2"-13 UNC bolt must be between 1/8" below, to
1/4" above, the surface of the AD-RP dryer mounting
bracket surface when fully installed and tightened to
50 lb-ft. Damage to the dryer body will result if the
bolt warning is ignored. Measure the thickness of
all materials that the three mounting bolts must pass
through. Small adjustments can be made using ﬂat
washers under the bolt heads. Do not use more than
three (3) ﬂat washers.
3. Mount the AD-RP air dryer on the vehicle using three
1/2" bolts (grade 5 min.) of the proper length and
washers. Torque to 50 lb-ft.

4.134 INCHES
CENTER TO CENTER

1/2” - 13 UNC
THREAD
(3 PLACES)

2.835 INCHES
CENTER TO
CENTER

FIGURE 7 - BENDIX® AD-RP™ SYSTEM PURGE AIR DRYER
MOUNTING BRACKET DIMENSIONS

PURGE CONTROL LINE
1. Install a purge control air line having a minimum inside
diameter of 3/16" between the Bendix® AD-RP™ air
dryer control port and an unused unloader port on the
governor. The control line must be plumbed direct to
the governor and not in series with automatic drain
valves, lubrication systems, etc.

WIDTH (THICKNESS)
OF AD-RP™ AIR DRYER
MOUNTING
BRACKET

2. The control line should slope downward to the AD-RP
dryer without forming potential water traps.

DISCHARGE LINE
GENERAL
Refer to Appendix A / Table A for recommended discharge
line lengths and sizes for various vehicle applications and
vocations.

PURGE EXHAUST LINE
1. If it is necessary to direct AD-RP air dryer discharge
contaminates away from vehicle components, a 1”
(25.4 mm) I.D. hose can be clamped on the AD-RP
dryer exhaust.

MOUNTING
BOLT
1/8” BELOW
SURFACE
OF MTG.
BRACKET

VEHICLE FRAME
MEMBER

MOUNTING
BOLT
MOUNTING BOLT
1/4” ABOVE
SURFACE OF
MOUNTING
BRACKET

WIRING THE HEATER/THERMOSTAT
1. Determine the vehicle's electrical system voltage and
make certain that the Bendix AD-RP air dryer that is to
be installed contains the same voltage heater. Conﬁrm
the proper voltage by noting the color of the heater and
thermostat connector.
The AD-RP air dryer is available with either a 12- or 24-volt
heater. Each uses 90 watts of power.
2. A separate wire harness and splice kit is with all
AD-RP air dryer replacements and retro-ﬁt kits. Refer
to the instructions contained in that kit for the proper
wiring procedure.

Heater & Thermostat Connector
Voltage
Color
12 Volts
White (No other markings)
24 Volts
Gray, or White w/Red Dot

FIGURE 8 - BENDIX® AD-RP™ SYSTEM PURGE AIR DRYER
MOUNTING BRACKET BOLT LENGTHS

TESTING THE BENDIX AD-RP AIR DRYER
GENERAL OPERATIONAL STATEMENT
The AD-RP remote purge air dryer, operates differently
than integral purge air dryers such as the Bendix® AD-9®
air dryer.
The "Remote Purge", designation is used because this air
dryer uses a small additional volume mounted on the frame
rail to purge or dry the desiccant material. During the purge
cycle, the pressure in this purge volume will drop to 0 psi.
This volume is separate from the air brake system volume,
no pressure drop in the air brake system should be caused
by the purge cycle of the AD-RP air dryer.

TESTING THE BENDIX® AD-RP™ AIR DRYER
Before placing the vehicle in service, perform the following
tests:
1. Close all reservoir drain cocks.
2. Build up system pressure to governor cut-out and
note that the Bendix® AD-RP™ air dryer purges with an
audible escape of air.
3. Apply and release the service brakes to reduce system
air pressure to governor cut-in. Note that the system
once again builds to full pressure and is followed by a
purge at the AD-RP air dryer exhaust.

4. It is recommended that the following items be tested
for leakage to ensure that the AD-RP air dryer will not
cycle excessively.
(A) Total air system leakage (See Bendix publication
BW5057 "Air Brake Handbook.")
(B) Compressor unloader mechanism
(C) Governor
(D) Drain cock and safety valve in the ﬁrst (supply)
reservoir
(E) All air connections leading to and from the ﬁrst
(supply) reservoir; and the
(F) Delivery check valve.

GOVERNOR

COMPRESSOR

FIGURE 9 - AIR SYSTEM WITHOUT BENDIX® AD-RP™ REMOTE PURGE AIR DRYER

BENDIX® AD-RP™
AIR DRYER

REMOTE PURGE
RESERVOIR

GOVERNOR

COMPRESSOR

FIGURE 10 - AIR SYSTEM WITH BENDIX® AD-RP REMOTE PURGE AIR DRYER

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS

CAUSE

1. Air dryer is constantly A. Excessive system leakage.
“cycling” or purging.
IMPORTANT: Note whether
Air dryer purges
air pressure loss is shown
frequently (every 4
on dash gauge(s). Pressure
minutes or less) while
loss shown on the gauges
vehicle is idling.
is caused by service brake
system or component
leakage. Pressure loss NOT
SHOWN on the gauges is
caused by supply system or
component leakage.

REMEDY
A. If leakage IS SHOWN on the gauges, test for
excessive service brake system leakage.
Allowable leakage:
Single vehicle - 1 psi / minute per service reservoir.
Tractor Trailer - 3 psi / minute per service reservoir.
Repair and retest as required.

If leakage is NOT SHOWN on gauges, test for
excessive supply system leakage.

Remove the drain cock, or valve, in the supply
reservoir (wet tank) and install an air gauge. Build
the system pressure, allow the air dryer to purge.
Observe the air gauge in the supply reservoir. The
pressure drop should not exceed 1 psi per minute.
Perform the following tests (1 to 5) in the order
presented.

(continued)
16

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS

CAUSE

1. Air dryer is constantly A. Excessive system leakage.
“cycling” or purging.
IMPORTANT: Note whether
Air dryer purges
air pressure loss is shown
frequently (every
on dash gauge(s). Pressure
4 minutes or less)
loss shown on gauges is
while vehicle is idling.
caused by service brake
(continued)
system or component
leakage. Pressure loss NOT
SHOWN on the gauges is
caused by supply system
or component leakage.
(continued)

REMEDY
A. Test ﬁttings, hoses, lines and connections. Apply
soap solution to detect excessive leakage. Tighten
or replace, as needed, then repeat the air dryer
charge/purge cycle and observe the gauge installed
in the supply reservoir. If the leakage is within limits,
remove the gauge from the reservoir and replace the
drain cock or valve. If excessive leakage is detected,
continue testing.
Test accessories connected to supply reservoir.
Drain all air pressure from the system, disconnect
all air lines leading to accessories (fan clutch,
wipers, air seats, etc.) and plug the reservoir at the
disconnection point. Build air system pressure until
the air dryer purges and observe the supply reservoir
gauge. If the leakage is no longer excessive, repair or
replace the leaking accessory. If excessive leakage
is detected, continue testing.
Test governor leakage. Build the system pressure to
governor cut-out, turn off the engine and apply a soap
solution to the governor exhaust port and around the
governor cap. Leakage should not exceed a one (1)
inch bubble in ﬁve (5) seconds. Reduce the system
pressure to 80 psi or less, and re-apply soap solution.
Leakage should not exceed a one (1) inch bubble in
ﬁve (5) seconds. If excessive leakage is detected in
either test, repair or replace the governor.
Test compressor unloader leakage. Drain all air
pressure from the system and remove the governor
from the compressor. Temporarily plug the governor
unloader port or the air line that mated with — or
connected to — the compressor. Build the air
system pressure until the air dryer purges, then
IMMEDIATELY SHUT OFF THE ENGINE. Observe
the air gauge in the supply reservoir. If the leakage
is within limits, replace the compressor unloaders.
Re-connect the governor to the compressor (after
removing the plug installed in governor) and retest
while observing the supply reservoir gauge. If
excessive leakage is detected, continue testing.
Test the air dryer purge valve and outlet (delivery)
check valve. Drain all air pressure from the system,
remove the control line connection at the air dryer,
and plug the end of the air line leading to the governor
(not the air dryer control port). Build the system
pressure to governor cut-out and observe the air
gauge. If little or no pressure drop is observed,
replace the air dryer check valve. If the pressure drop
continues, apply a soap solution to the air dryer purge
exhaust and purge control port (where the control
line was removed). Leakage should not exceed a
one (1) inch bubble in ﬁve (5) seconds. If leakage is
excessive, repair or replace purge valve assembly.
(continued)
17

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS

CAUSE

1. Air dryer is constantly B. Incorrect governor setting or
“cycling” or purging.
malfunctioning governor.
Air dryer purges
frequently (every 4
minutes or less) while
vehicle is idling.
C. Rapid cycling of the
governor due to air
starvation at the reservoir
(RES) port of the governor.

2. Water and/or oil in
supply or service
reservoir.

REMEDY
B. Minimum setting required for Bendix® AD-RP™ air
dryer installation is 100 psi cut-in and 120 psi cut-out.
Test operation of the governor. Repair or replace as
necessary.
C. With a gauge installed at the RES port of the
governor, the pressure should not drop below cut-in
pressure at the onset of the compressor "unloaded"
cycle. If the pressure drops, check for "kinks" or
restrictions in the line connected to the RES port.
The line connected to the RES port on the governor
must be the same diameter, or preferably larger, than
the lines connected to the UNL port(s) on governor.

D. High air usage vehicle
application.

D. Refer to the "Vehicle Application Requirements"
section of this manual and verify the application.

A. Improper discharge line
length or improper line
material. Maximum air
dryer inlet temperature is
exceeded.

A. Refer to the section titled "Connecting the Air Lines"
and Appendix A / Table A / columns 1 & 2, then check
the line size and length.

B. Air system charged from an
outside air source (outside
air not passing through air
dryer).

B. If the system must have an outside air ﬁll provision,
outside air should pass through air dryer. This
practice should be minimized.

C. Air dryer is not purging.

C. See Symptom #5.

D. Purge (air exhaust) time
insufﬁcient due to excessive
system leakage.

D. Check causes and remedies for Symptom #1.

(continued)
18

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
2. Water and/or oil in
supply or service
reservoir. (continued)

CAUSE
E. Excessive air usage, duty
cycle is too high; the air
dryer is not compatible
with the vehicle air system
requirement (improper air
dryer/vehicle application).
NOTE: Duty cycle is the ratio
of time the compressor spends
building air to total engine
running time. Air compressors
are designed to build air
(run “loaded”) up to 25% of
the time. Higher duty cycles
cause conditions that affect
air brake charging system
performance which may
require additional maintenance.
Factors that add to the duty
cycle are: air suspension,
additional air accessories,
use of an undersized
compressor, frequent stops,
excessive leakage from ﬁttings,
connections, lines, chambers or
valves, etc.

REMEDY
E. See Appendix A / Table A /c olumn 1 for the
recommended compressor sizes. If the compressor
is “too small” for the vehicle vocation (for example,
where a vehicle’s vocation has changed, or service
conditions exceed the original vehicle or engine
OE specs), then upgrade the compressor. Note:
The costs incurred (e.g. installing a larger capacity
compressor, etc.) are not covered under the original
compressor warranty.
Charge Cycle Time - The Bendix® AD-RP™ air dryer
is designed to provide clean, dry air for the brake
system. When a vehicle’s air system is used to
operate non-brake air accessories, the compressor
should recover from governor cut-in to governor
cut-out (usually 100 psi to 120 psi) in 90 seconds
or less at engine RPMs commensurate with the
vehicle vocation. If the recovery time consistently
exceeds this limit, it may be necessary to “by-pass”
the air accessory responsible for the high air usage.
An example of where a by-pass system would
be required is when the compressor is used to
pressurize a tank trailer for purposes of off-loading
product. Consult your local authorized Bendix ®
parts outlet or sales representative for additional
information.
Purge Cycle Time - During normal vehicle operation,
the air compressor must remain unloaded for a
minimum of 30 seconds. This minimum purge time
is required to ensure complete regeneration of the
desiccant material. If the purge time is consistently
less than the minimum, an accessory bypass system
must be installed. Consult your local authorized
Bendix parts outlet or sales representative for
additional information.
Air Compressor Size - The AD-RP air dryer was
designed primarily for use with compressors rated up
to 30 CFM. Contact an authorized Bendix parts outlet
or a Bendix sales representative for assistance when
using the AD-RP dryer with a compressor which has
a rated displacement exceeding 30 CFM.

(continued)
19

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
2. Water and/or oil in
supply or service
reservoir. (continued)

CAUSE
F. Air compressor discharge
and/or air dryer inlet
temperature is too high.

REMEDY
F. Restricted discharge line - See Appendix A/ Table A/
column 1 & 2 for recommended sizes. If discharge
line is restricted — or more than 1/16" carbon build
up is found — replace the discharge line. Replace
as necessary.
Discharge Line Freeze-Up - The discharge line
must maintain a constant slope down from the
compressor to the air dryer inlet ﬁtting to avoid low
points where ice may form and block the ﬂow. If,
instead, ice blockages occur at the air dryer inlet,
insulation may be added here. Or, if the inlet ﬁtting
is a typical 90° ﬁtting, the ﬁtting may be changed to
a straight or a 45° ﬁtting. For more information on
how to help prevent discharge line freeze-ups, see
Bendix Bulletins TCH-008-021 and TCH-008-022.
Shorter discharge line lengths or insulation may be
required in cold climates.
Insufficient coolant flow through compressor Inspect the Bendix AD-RP™ air dryer was designed
primarily for use with compressors rated up to 30
CFM. Contact an authorized Bendix parts outlet or
a Bendix sales representative for assistance when
using the dryer with a compressor which has a rated
displacement exceeding 30 CFM.
Coolant line - Replace as necessary (I.D. is 1/2"
min.). Inspect the coolant lines for kinks and
restrictions, and the ﬁttings for restrictions. Replace
as necessary. Verify coolant lines go from the engine
block to compressor and back to the water pump.
Repair as necessary.
Restricted air inlet (not enough air to compressor).
Check the compressor air inlet line for restrictions,
brittleness, soft or sagging hose conditions, etc.
Repair as necessary. Inlet line size is 3/4 I.D. the
maximum restriction requirement for compressors
is 25 inches of water. Check the engine air ﬁlter and
service if necessary (if possible, check the air ﬁlter
usage indicator).

(continued)
20

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
2. Water and/or oil in
supply or service
reservoir. (continued)

3. Oil present at air
dryer purge exhaust
or cartridge during
maintenance.

CAUSE

REMEDY

F. Air compressor discharge
and/or air dryer inlet
temperature is too high.
(continued)

Poorly ﬁltered inlet air (poor air quality to compressor).
Check for leaking, damaged or malfunctioning
compressor air inlet components (e.g. induction line,
ﬁttings, gaskets, ﬁlter bodies, etc.). Repair the inlet
components as needed. Note: Dirt ingestion will
damage the compressor and is not covered under
warranty. If you found excessive oil in the service
reservoir and you did not ﬁnd any issues above,
the compressor may be passing oil. Replace the
compressor and — if still under warranty — follow
the normal warranty process.

G. Compressor malfunction.

G. If you found excessive oil present in the service
reservoir and you did not ﬁnd any issues above, the
compressor may be passing oil. Test the compressor
using the Bendix® BASIC™ cup method as described
in the Bendix compressor service manual and
referred to in Appendix A/Table A/column 5. Replace
the compressor and — if it is still under warranty —
follow the normal warranty process.

H. Air by-passes the desiccant
cartridge assembly.

H. When replacing the desiccant cartridge, make sure
the desiccant cartridge assembly is properly installed
and sealing rings are in place on the mounting
surface of the desiccant cartridge.

Desiccant cartridge requires
replacement.

I. Replace the desiccant cartridge assembly. Refer to
Appendix A/Table A/columns 3 & 4 for recommended
intervals.

A. Air brake charging system is
functioning normally.

A. Air dryers remove water and oil from the air brake
charging system. A small amount of oil is normal.
Check that regular maintenance is being performed
and that the amount of oil in the air tanks (reservoirs)
is within the acceptable range shown on the BASIC
cup (see also column 5 of Appendix A/Table A).
Replace the air dryer cartridge as needed and return
the vehicle to service.

4. Air is escaping from
A. Air dryer purge valve
air dryer exhaust
leaking.
during the charge
B. Compressor unloader
cycle but able to build
mechanism malfunction.
system air pressure.
(Compressor
pumping.)
C. Governor malfunction.

A. Repair or replace air dryer purge valve.
B. One or both dash air gauges should show higher than
normal air pressure. Test the compressor unloader
mechanism for proper operation. Repair or replace
unloaders as necessary.
C. One or both dash air gauges may show higher than
normal air pressure. Test the governor for proper
operation. Repair or replace as necessary.

(continued)
21

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS

CAUSE

4. Air is escaping from
D. Air ﬂow to the supply
air dryer exhaust
reservoir is restricted.
during the charge
cycle, but is able
to build system
air pressure.
(Compressor
pumping.) (continued)

REMEDY
D. Kinked, plugged, damaged hose tubing or ﬁttings:
Check to determine if air is reaching the ﬁrst reservoir.
Inspect for kinked tubing or hose. Check for undrilled
ﬁttings or restricted hose or tubing ﬁttings. Repair or
replace as necessary.
Desiccant cartridge plugged: Check compressor
for excessive oil passing and/or correct compressor
installation. Repair or replace as necessary. Replace
the desiccant cartridge.

E. Excessive pressure
E. Increase the volume in the discharge line by adjusting
pulsations from compressor.
the length or size of line, or add a ping tank.
(Typical single cylinder type.)
5. Air escaping from air
dryer exhaust port
during entire purge
cycle. (Compressor
not running.)

A. Leaking turbo cut-off valve in A. Note the dash gauges to verify the purge cycle has
ended. Perform the air dryer “Operation & Leakage
Bendix® AD-RP™ air dryer.
Tests” speciﬁed in this manual. Repair or replace as
necessary.
B. Leaking purge piston o-ring
in the AD-RP air dryer.

B. Perform the Air Dryer “Operation & Leakage Tests”
specified in this manual. Repair or replace as
necessary.

C. Leaking delivery check
valve.

C. Perform the Air Dryer “Operation & Leakage Tests”
specified in this manual. Repair or replace as
necessary.

6. Unable to build air
A. Frozen discharge line.
system pressure and
air is not escaping
from the AD-RP air
dryer exhaust during
B. Compressor unloader
the charge cycle.
mechanism malfunction.
(Note: This is not the
same as symptom
C. Governor malfunction.
4.)

A. Inspect the discharge line installation for water traps
that could freeze. Refer to “Connecting The Air Lines”
section in manual. Repair or replace as necessary.
B. Test the compressor unloader mechanism for proper
operation. Repair or replace as necessary.
C. Test the governor for proper operation. Repair or
replace as necessary.

D. Air ﬂow to service brake
D. Check for kinked, plugged, damaged hose tubing or
system is restricted or
ﬁttings in the air line between the supply reservoir
plugged. Air pressure on one
and low pressure service reservoir.
dash gauge normal with no,
or low pressure on the other
gauge.

(continued)
22

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
7. Unable to build air
system pressure.

8. Air dryer does not
purge or exhaust air.
Note: this symptom
often precedes
Symptom #9 if
desiccant cartridge is
not replaced.

CAUSE
®

™

REMEDY

A. Bendix AD-RP air dryer
purge control line incorrectly
connected to governor.

A. Check that the purge control of the AD-RP air
dryer is connected to the UNL (unloader) port on
governor.

B. Air trapped in the purge
control line (between the
governor and the AD-RP air
dryer.)

B. Inspect for kinked, plugged, damaged hose tubing
or ﬁttings. Check for undrilled ﬁttings or restricted
hose or tubing fittings. Repair or replace as
necessary.

C. Governor malfunction.

C. Test the governor operation. Repair or replace as
necessary.

D. Compressor unloader
mechanism malfunction.

D. Test the compressor unloader mechanism for
proper operation. Repair or replace as necessary.

E. The AD-RP air dryer purge
valve piston is frozen open.

E. Check the operation of the AD-RP air dryer heater
and thermostat. Repair or replace as necessary.

F. The AD-RP air dryer purge
valve piston is stuck.

F. Check the operation and repair or replace as
necessary.

A. Air is not reaching the
AD-RP air dryer purge
control port.

A. Test to determine that air ﬂows through the purge
control line to the purge control port on the AD-RP
air dryer when the compressor is unloaded. Check
for undrilled ﬁttings. Check if the purge control line
is broken, not connected, mis-connected, frozen or
damaged. Inspect, repair or replace as necessary.
Replace desiccant cartridge.

B. The AD-RP air dryer purge
valve or piston is frozen
closed.

B. Check the operation of the AD-RP air dryer heater
and thermostat. Repair or replace as necessary.
Replace desiccant cartridge.

C. Extremely high air usage
requirements on the
vehicle.

C. Refer to the Vehicle Application Requirements
section of this manual and verify application.

(continued)
23

Bendix® AD-RP™ AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
9. Desiccant material
is being expelled
from the air dryer
purge valve exhaust
(may look like
whitish liquid, paste,
or small beads). –
OR Unsatisfactory
desiccant life.

CAUSE

REMEDY

A. This symptom is almost
always accompanied by
one or more of Symptoms
1, 2, 3, 4 and 6. See the
related causes for these
symptoms.

A. See the related remedies for the causes under
Symptoms 1, 2, 3, 4 and 6*.

B. Air dryer not securely
mounted. (Excessive
vibration.)

B. Vibration should be held to minimum. Add bracket
supports or change the air dryer mounting location
if necessary*.

C. Defective desiccant
cartridge.

C. Replace*.

D. Compressor passing
excessive oil.

D. Check for proper compressor installation; if
symptoms persist, replace compressor*.

E. Air dryer has not purged for
an extended period.

E. Refer to Symptom #7 Causes and Remedies*.

10. “Pinging” noise
excessive during
compressor loaded
cycle.

A. A single cylinder
compressor with high pulse
cycles.

A. A slight “pinging” sound may be heard during
system build up when a single cylinder compressor
is used. If this sound is deemed objectionable, it
can be reduced substantially by increasing the
discharge line volume. This can be accomplished
by adding an additional four feet of discharge line,
or adding a 90 cubic inch reservoir between the
compressor and the Bendix® AD-RP™ air dryer.

11. The air dryer purge
piston cycles rapidly
in the compressor
unloaded (noncompressing) mode.

A. Compressor fails to
“unload.”

A. Faulty governor installation: no air line from the
governor to the compressor, or the line is “kinked”
or restricted. Install or repair the air line.

* If desiccant material is being expelled, the cartridge and purge valve must be removed from the air dryer and
the desiccant material must be removed from the interior of the dryer. Clean the interior surfaces of the dryer
and install a new cartridge. Clean and inspect the purge valve before re-installation, or replace with a new purge
valve.

NOTES

Appendix A
Table A: Maintenance Schedule and Usage Guidelines
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system.

Vehicle Used for:

No. of
Axles

Column 1

Column 2

Typical
Compressors
Spec'd

Discharge
Line
I.D.

Length

1/2 in.

6 ft.

Column 3
Recommended
Air Dryer
Cartridge
Replacement1

Column 4
Recommended
Reservoir
Drain
Schedule2

Column 5
Acceptable
Reservoir
Oil Contents3
at Regular
Drain Interval

Low Air Use
5
or
less

e.g. Line haul single trailer
with air suspension,
school bus.

5
or
less

High Air Use

e.g. Double/triple trailer, open
highway coach/RV, (most)
pick-up & delivery, yard or
terminal jockey, off-highway,
construction, loggers, concrete
mixer, dump truck, ﬁre truck.

8
or
less

Compressor with up to 25% duty cycle

e.g. City transit bus, refuse,
bulk unloaders, low boys,
urban region coach, central tire
inﬂation.

12
or
less

Bendix® Tu-Flo® 750 air compressor

Compressor with up to 25% duty cycle

Bendix® BA-921® air compressor

Compressor with up to 25% duty cycle

For oil carry-over
control4 suggested
upgrades:

5/8 in.
1/2 in.

9 ft.
9 ft.

Every 3
Years

For oil carry-over
control4 suggested
upgrades:

5/8 in.

1/2 in.

5/8 in.

12 ft.
Every 2
Years

15 ft.

Every
Month
5/8 in.

12 ft.

For oil carry-over
control4 suggested
upgrades:

3/4 in.

Bendix®
BASIC™ test
acceptable
range:
3 oil units
per month.
See
Appendix A.

For the
BASIC
Test Kit:
Order
Bendix
P/N
5013711

BASIC test
acceptable
range:
5 oil units
per month.
See
Appendix
A.

Every
Year

15 ft.

Footnotes:
1 With increased air demand the air dryer cartridge needs to be replaced more often.
2 Use the drain valves to slowly drain all reservoirs to zero psi.
3 Allow the oil/water mixture to fully settle before measuring oil quantity.
4 To counter above normal temperatures at the air dryer inlet, (and resultant oil-vapor passing upstream
in the air system) replace the discharge line with one of a larger diameter and/or longer length. This
helps reduce the air's temperature. If sufﬁcient cooling occurs, the oil-vapor condenses and can be
removed by the air dryer. Discharge line upgrades are not covered under warranty. Note: To help prevent
discharge line freeze-ups, shorter discharge line lengths or insulation may be required in cold climates.
(See Bendix Bulletins TCH-008-021 and TCH-008-022, included in Appendix B, for more information.)
5 For certain vehicles/applications, where turbo-charged inlet air is used, a smaller size compressor may
be permissible.

Recommended
Every
Month max of
every 90
days

12 ft.

For oil carry-over
control4 suggested
upgrades:
Bendix® BA-922®, or DuraFlo 596™ air compressor

e.g. Line haul single trailer
w/o air suspension, air over
hydraulic brakes.

Bendix® Tu-Flo® 550 air compressor

Compressor with less than 15% duty cycle

Note: Compressor and/or air dryer
upgrades are recommended in
cases where duty cycle is greater
than the normal range (for the
examples above).
For Bendix® Tu-Flo® 550 and 750
compressors, unloader service
is recommended every 250,000
miles.

Appendix B
For more troubleshooting information refer to Troubleshooting Charging and Air Supply Systems (BW1779). This and
other literature are available, online, from the Bendix Literature Center on www.bendix.com.

STANDARD SINGLE CHECK VALVE
(USED W/INTEGRAL PURGE AIR
DRYERS)

GOVERNOR

LOW PRESSURE
INDICATOR
DASH
GAUGE

CONVENTIONAL
SUPPLY SYSTEM
& INTEGRAL PURGE
AIR DRYER

REAR

SAFETY
VALVE
SUPPLY
TWO CYLINDER.
COMPRESSOR

AIR DRYER

FRONT
STANDARD SINGLE
CHECK VALVE
SAFETY
VALVE

GOVERNOR

HOLSET TYPE
"E & QE"
COMPRESSOR
WITH ECON
VALVE

AIR
DRYER

REAR

LOW
PRESSURE
INDICATOR

SUPPLY

HOLSET
“E OR QE”
COMPRESSOR

FRONT

HOLSET
ECON VALVE

SPECIAL
SINGLE CHECK
("CHOKE" IN INLET)

STANDARD SINGLE
CHECK VALVE
SAFETY
VALVE

GOVERNOR

HOLSET TYPE
"E & QE"
COMPRESSOR
W/O ECON
VALVE

DASH
GAUGE

AIR DRYER

DRAIN COCK

LOW PRESSURE
INDICATOR

REAR

DASH
GAUGE

SUPPLY

HOLSET
“E OR QE”
COMPRESSOR
SPECIAL
SINGLE CHECK
("CHOKE" IN INLET)

SINGLE CHECK PROTECTION VALVE
(USED W/SYSTEM
PURGE AIR DRYERS)

FRONT

SINGLE CHECK VALVE (USED
W/INTEGRAL PURGE AIR DRYERS)

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Bendix Sd 08 2415A Users Manual 2415A_US_001

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