Bendix Commercial Vehicle Systems AD-4 AIR DRYER 10/04 User Manual
®
Bendix® AD-4™ Air Dryer
SD-08-2407
SUPPLY
PORT
THERMOSTAT
TERMINAL
EXTENDED PURGE AD-4™ AIR DRYER STANDARD AD-4™ AIR DRYER
FIGURE 1 - AD-4™ AIR DRYER MODELS
PURGE
EXHAUST
UPPER
BRACKET
LOWER
BRACKET
CONTROL
PORT
DELIVERY PORT
UPPER
BRACKET
LOWER
BRACKET
SUPPLY
PORT
PURGE
EXHAUST
DESCRIPTION
The function of the AD-4™ air dryer 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 AD-4™ air dryer consists of a desiccant cartridge and a
die cast aluminum end cover secured to a cylindrical steel
outer shell with eight cap screws and nuts. The end cover
contains a check valve assembly , a safety valve, purge valve
mechanism, a cast-in heater element with a replaceable
thermostat assembly and three threaded air connections.
The three air connections are identified with embossed
numbers and lettering. The identification and function of each
is as follows:
Port l.D. Function/Connection
CON 4................ Control Port
(from unloader port on governor).
SUP 11 .............. Supply Port (air in).
DEL 2 ................ Delivery Port (air out).
A cast-in heater element and replaceable thermostat with
an external terminal are provided.
The voltage and wattage requirements of the heater and
thermostat are shown with embossed numbers and letters
in the recess adjacent to the control port marked “CON.”
1
CHECK
VALVE
ORIFICE
DESICCANT
CARTRIDGE
CHECK
VALVE
DELIVERY
PORT
HEATER
PURGE
VALVE
SUPPLY RESERVOIR
FIGURE 2 - AD-4™ AIR DRYER CHARGE CYCLE
OPERA TION OF THE AD-4™ AIR DRYER
EXHAUST
PORT
CONTROL
GOVERNOR
PURGE VOLUME
DESICCANT
BED
OIL SEPARATOR
COMPRESSOR
The AD-4™ air dryer alternates between two operational
modes or “cycles” during operation: the charge cycle and
the purge cycle. The following description of operation is
separated into these “cycles” of operation.
CHARGE CYCLE (refer to Figure 2)
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 end cover. The flow velocity or the
speed at which the air and its contaminants travel down the
discharge line is reduced substantially as it enters the air
dryer end cover baffle system behind the supply port. As air
travels through the baffle system, its direction of flow changes
by 180 degrees several times, reducing the temperature,
causing contaminants to condense and drop to the bottom
or sump of the air dryer end cover.
After exiting the end cover baffle system, the air flows into
the desiccant cartridge. Once in the desiccant cartridge air
first flows through an oil separator which removes water in
liquid form as well as oil, oil vapor and solid contaminants.
Air exits the oil separator and enters the desiccant drying
bed. Air flowing through the column of desiccant becomes
progressively dryer as water vapor adheres to the desiccant
material in a process known as “adsorption”. The desiccant
cartridge using the adsorption process typically removes
95% of the water vapor from the pressurized air.
The majority of dry air exits the desiccant cartridge through
its integral single check valve to fill the purge volume between
the desiccant cartridge and outer shell. Some air will also
exit the desiccant cartridge through the purge orifice adjacent
to the check valve.
Dry air flows out of the purge volume through the single
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 air brake
system pressure builds to the governor cutout setting.
PURGE CYCLE (refer to Figure 3)
When air brake system pressure reaches the cutout setting
of the governor, the compressor unloads (air compression
stopped) and the purge cycle of the air dryer begins. The
2
CHECK
VALVE
ORIFICE
DESICCANT
CARTRIDGE
CHECK
VALVE
DELIVERY
PORT
HEATER
PURGE
VALVE
FIGURE 3 - AD-4™ AIR DRYER PURGE CYCLE
EXHAUST
SUPPLY RESERVOIR
PORT
CONTROL
GOVERNOR
PURGE VOLUME
DESICCANT
BED
OIL SEPARATOR
COMPRESSOR
line connecting the governor unloader port to the AD-4™ air
dryer end cover control port is pressurized when the governor
unloads the compressor. Air pressure at the AD-4™ air dryer
end cover control port is also present on the purge valve
piston. The purge piston moves in response to air pressure
causing the purge valve to open to atmosphere.
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. Oil, water
and solid contaminants collected by the oil separator are
removed by air flowing from 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-4™ air dryer exhaust.
The actual reactivation of the desiccant drying bed begins
as dry air flows from the purge volume through the desiccant
cartridge purge orifice and into the desiccant drying 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 15-30 seconds are required
for the entire purge volume of a standard AD-4™ air dryer to
flow through the desiccant drying bed.
The end cover single check valve assembly prevents air
pressure in the brake system from returning to the air dryer
during the purge cycle. Af ter the 30 second purge cycle is
complete, the air dryer is ready for the next charge cycle to
begin.
The purge valve will remain open after the purge cycle is
complete and will not close until air brake system pressure
is reduced and the governor signals the compressor to
charge.
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.
3
CHECK
VALVE
PURGE
ORIFICE
DESICCANT
CARTRIDGE
CHECK VALVE
ASSEMBLY
NUT
WASHER
END COVER
SPECIAL
WASHER
HEX HEAD
SCREW
FIGURE 4 - AD-4™ AIR DRYER SECTIONAL VIEW
DELIVERY
PORT
PURGE
VALVE
EXHAUST
DIAPHRAGM
PURGE PISTON
EXHAUST
COVER
PURGE VOLUME
DESICCANT
BED
PERFORATED PLATE
OIL SEPARATOR
SEALING RING
SEALING RING
SEALING RING
SEALING RING
SPRING
O-RING
SUPPLY
PORT
Every 900 operating hours or 25,000 miles or every three
(3) months:
1. Check for moisture in the air brake system by opening
reservoirs, drain cocks, or valves and checking for
presence of water. If moisture is present, the desiccant
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 did 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, T able A and the column entitled V ehicle
Vocation.
C. The air dryer has been installed in a system that
has been previously used without an air dryer. This
type 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 AD-4™ Air Dryer On
Vehicle section and 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 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 may be normal
and should not, in itself, be considered a reason to
replace the desiccant; oil stained desiccant can function
adequately.
4
2. Check mounting bolts for tightness. Retorque to 270385 inch pounds.
3. Perform the Operation & Leakage Tests listed in this
publication.
Every 10,800 hours or 300,000 miles or 36 months:
1. Rebuild the air dryer including the 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 assure that replacement occurs only when necessary ,
it is important that Operation & Leakage T ests be performed.
WARNING!
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
6. Check the operation of the end cover heater and
thermostat assembly during cold weather operation as
follows:
A. Electric Power to the Dryer
With the ignition or engine kill switch in the ON
position, check for power at the dryer’s electrical
terminal using a voltmeter or test light. On a single
terminal AD-4™ air dryer’s disconnect the lead wire
at the end cover terminal post. Place the test leads
on the lead wire and a GOOD vehicle ground. On
dual terminal AD-4™ air dryer’s disconnect both lead
wires at the end cover terminal posts. If there is no
voltage indicated, 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 end cover
assembly to below 40 degrees Fahrenheit. Using an
ohmmeter, check the resistance between the
electrical terminal and the metal end cover (see Figure
5). (Note: On the dual terminal end cover, check the
resistance between the two terminals.) The
1. Test the outlet port check valve assembly by building
the air system to governor cut-out and observing a test
air gauge installed in the supply reservoir. A rapid loss of
pressure could indicate a failed outlet port check valve.
(Note: Purge valve will be open when governor cut-out
pressure is reached. Allow 45 seconds after governor
cut-out occurs to complete the purge cycle before testing
the check valve.) Coat the exhaust with a soap solution.
Leakage should not exceed a 1" bubble in 1 second.
2. Check for excessive leakage around the purge valve.
With the compressor in loaded mode (compressing air),
apply a soap solution to the purge valve housing
assembly exhaust port and observe that leakage does
not exceed a 1" bubble in 1 second. If the leakage
exceeds the maximum specified, service the purge valve
housing assembly .
3. Close all reservoir drain cocks. Build up system pressure
to governor cut-out and note that AD-4™ air dryer purges
with an audible escape of air. “Fan” 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 AD-4™ air dryer purge.
4. Check the operation of the safety valve by pulling the
exposed stem while the compressor is loaded
(compressing air). There must be an exhaust of air while
the stem is held and the valve should reseat when the
stem is released.
5. Check all lines and fittings leading to and from the air
dryer for leakage and integrity .
HEATER POST
A
B
BOLD NUMBERS ARE ITEMS IN MAINTENANCE KITS
11
8
6
5
4
3
2
1
FIGURE 5 - AD-4™ AIR DRYER SINGLE AND DUAL
TERMINAL THERMOSTAT ASSEMBLIES
9
8
THERMOSTAT
COVER
1
SINGLE WIRE SYSTEM
BOOT
DUAL WIRE SYSTEM
5
3
CONNECTIONS FOR POWER
AND INSULATED RETURN
2
1
1
1
9
10
7
11
6
4
9
10
7
BOOT
5
resistance should be 2.0 to 4.0 ohms for the 12 volt,
60 watt end cover and 4.0 - 7.0 ohms for the 24 volt,
120 watt end cover. These resist ance values apply
to either single or dual terminal air dryer end covers.
Warm the end cover assembly to over 90 degrees
Fahrenheit and again check the resistance as above.
The resistance should exceed 1000 ohms for both
single and dual terminal air dryers. 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, proceed to Step C to determine the
cause.
C. Heater Element Inspection
With the ignition or engine control switch “off”, remove
the thermostat cover (see Figure 5). Using an
ohmmeter, check the resistance between the met al
end cover and the heater post (see Figure 5). (Note:
On the dual terminal end cover, check the resist ance
between the two terminals.) For a 12 volt, 60 watt
end cover, the resistance should be 2.0 - 2.8 ohms
and for a 24 volt, 120 watt end cover, 4.0 - 5.6 ohms.
These resistance values apply to either single or dual
terminal air dryer end covers. If the heater resistance
value obtained is outside the stated limits, a new or
remanufactured end cover should be installed, since
the heater element cannot be serviced. Check that
a good ground path exists between the air dryer end
cover casting and the vehicle chassis. Correct if
needed. If the heater resistance value obtained is
within the stated limits the thermostat should be
replaced (Kit Number 102657) or a new or
remanufactured end cover installed. Note: The dual
terminal air dryer cover requires kit number 103982.
D. Reassembly
Reinstall the thermostat cover as illustrated in Figure
5. Take special care to assure the rubber spacer
and the gasket are correctly installed, to assure
proper operation.
REBUILDING THE AD-4™ AIR DRYER
GENERAL
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
following list to find the appropriate kit(s).
When rebuilding or replacing components of the air dryer
use only genuine Bendix parts. For ease in servicing the
AD-4™ air dryer desiccant cartridge assembly, it is
recommended that the air dryer be removed from the vehicle.
MAINTENANCE KITS A V AILABLE:
103817 Major Maintenance Kit
This kit contains the parts necessary to completely
rebuild the AD-4™ air dryer (desiccant cartridge
included) and includes kit 103980.
103818
103879 AD-4™ Air Dryer Seal Kit
103980 End Cover Maintenance Kit
103981 Desiccant Cartridge Replacement Kit
102657 Thermostat Maintenance Kit (single terminal
103982 Thermostat Maintenance Kit (dual terminal
288918 Thermostat Cover Replacement Kit (single
104964 Thermostat Cover Replacement Kit (dual terminal
AD-4™ Air Dryer Purge V alve Maintenance Kit
This kit contains the parts necessary to rebuild the
™
AD-4
air dryer end cover purge valve only .
This kit contains the outlet port check valve and the
o-rings and seals required when removing the end
cover assembly . This kit is included with kits 103980
and 103981.
This kit contains the parts necessary to rebuild the
end cover of the AD-4™ air dryer and includes kit
103818.
This kit contains the parts necessary to change
the desiccant cartridge only .
models)
This kit contains the parts necessary to rebuild a
single terminal thermostat assembly in the AD-4
air dryer.
models)
This kit contains the parts necessary to rebuild a
two terminal thermostat assembly (insulated
ground).
terminal models)
This kit contains the necessary components for
replacing the non-metallic thermostat cover .
models)
This kit contains the necessary components for
replacing the non-metallic thermostat cover .
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove 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.
™
6
MOUNTING STRAP
CAP SCREW
5/16” X 4-1/2”
LOCKWASHER
BRACKET
MOUNTING STRAP
CAP SCREW
5/16” X 4-1/2”
BRACKET
MOUNTING BRACKET HOOK
AIR DRYER
HOUSING
NUT
NUT
(8) LOCK NUT
LOCKWASHER
(8) SPECIAL
WASHER
CHECK VALVE
ASSEMBLY
DELIVERY
PORT
SEALING RING
SEALING PLATE
(4) DESICCANT CARTRIDGE
CAP SCREW
& LOCKWASHER
SEALING RING
SEALING RING
PURGE PISTON
O-RING
SPRING
CONTROL
PORT
SUPPLY PORT
END COVER
HEATER
VOLTAGE
SHOWN
DESICCANT
CARTRIDGE
SEALING RING
FIGURE 6 - AD-4™ AIR DRYER ASSEMBLY
SAFETY
VALVE
SPECIAL
WASHER
(8) CAP SCREW 3/8”
PURGE VALVE
EXHAUST
DIAPHRAGM
1/2” CAP SCREW
EXHAUST COVER
SCREW
THERMOSTAT
ASSEMBLY
7
3. 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.
4. 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 an AD-IS
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommended procedures, deactivate the electrical
system in a manner that safely removes all
electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. 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.
8. Use only genuine Bendix® 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.
9. 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.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored to
their proper operating condition.
11. For vehicles with Antilock 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.
AD-4™ AIR DRYER REMOVAL
1. Park the vehicle on a level surface and prevent movement
by means other than the brakes.
2. Drain all reservoirs to 0 p.s.i. (0 kPa).— Caution:
Compressor discharge line may still contain residual
pressure.
3. Identify and disconnect the three air lines from the end
cover and note the position of end cover ports relative to
the vehicle.
4. Pull boot from the thermostat and heater cover and slide
it onto the wire to expose the connection. Remove nut
and disconnect electrical wire from the terminal. Note:
Vehicles with insulated ground (2 wire) system will have
two boots and two terminals to be disconnected. (See
Figures 5 & 8.)
5. Loosen the 5/16" X 4-1/2" hex bolt securing the upper
and lower mounting straps. Disengage the mounting
LOWER RIGHT ANGLE
BRACKET
™
END
COVER
FIGURE 7 - LOWER BRACKET INSTALLATION
EXTRA
LONG
CAP SCREW
LOCK NUT
bracket hook from the end cover (Refer to Figure 6.)
Note: If the AD-4™ air dryer being serviced has a right
angle bracket instead of a lower mounting strap and
safety hook, proceed to step 6, otherwise proceed to
step 7.
6. Remove, retain and mark the two 3/8" end cover cap
screws, lock nuts and four special washers that retain
the lower mounting bracket to the end cover, also mark
these two holes of the end cover. (These bolts are longer
than the other 6 bolts.)
7. Remove the AD-4™ air dryer from its mounting brackets
on the vehicle.
DISASSEMBLY
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that a
major rebuild of the AD-4™ air dryer is being undertaken.
Several replacement parts and maintenance kits are available
which do not require full disassembly. The instructions
provided with these parts and kits should be followed in lieu
of the instructions presented here. Refer to Figure 6 during
disassembly.
Caution: While performing service on the AD-4™ 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 end cover, install a pipe nipple in the supply port
and clamp the nipple into a vise.
1. Remove the remaining 3/8" lock nuts, special washers
and cap screws from the flange of the air dryer and
separate the end cover from the air dryer outer housing.
Separate the desiccant cartridge and sealing plate from
SPECIAL
WASHER
8
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