The air dryer collects and removes moisture and
contaminants before the air reaches the first reservoir. It is
distinctly different than a reservoir drain valve or aftercooler
in that it provides “dry air” for the air brake system. The
daily draining of the system’s reservoirs is no longer
necessary, thus reducing maintenance considerably when
compared to an air brake system without an air dryer.
In a system without an air dryer, the life of air brake
components is substantially reduced because of contact
with water and oil in the system and since the air dryer
removes water and oil in vapor form, life of the component
devices is substantially increased when the air dryer is used.
™
AD-2
AIR DRYERAD-1™ AIR DRYER
The air dryer can be used on most highway vehicles where
normal compressor loaded time is 90 seconds or less and
unloaded time is 30 seconds or more. If the compressor
remains loaded for long periods of time, such as on a transit
bus, certain changes in the purge volume of the dryer must
be made. For more information regarding increase of the
purge volume, contact our Engineering Department, in Elyria,
Ohio.
The air dryer is installed in the discharge line between the
compressor and the first reservoir. The unit must be mounted
vertically and mounting brackets are provided and can be
adjusted to meet installation requirements.
1
The housing assembly consists of two cylindrical steel
stampings welded together. For piping convenience, two inlet
ports, one reservoir port and one purge volume port are
provided in the AD-2™ air dryer. The side outlet port of the
AD-2™ air dryer incorporates an integral single check valve
with the top port used for the addition of purge volume.
(Refer to Figure 1)
A safety valve mounted in the housing assembly protects
against excessive pressure build-up within the housing.
The desiccant sealing plate assembly is located mid-way
in the housing assembly and houses a replaceable ball-type
single check. Also located in the plate assembly is the purge
orifice.
5-1/2”
PURGE
VOLUME
OUTLET
The desiccant cartridge and aluminum oil separator filter
are removable and comprise a complete serviceable unit.
The desiccant beads, which are referred to as the “drying
bed”, are a drying substance that has the unique property
of exposing a tremendous surface area in proportion to its
bulk. One pound of the desiccant beads has about two
million square feet of adsorptive area made up of a large
number of submicroscopic cavities in each bead. Each
desiccant bead adsorbs or collects moisture.
CHECK
VALVE
19-1/2”
DESICCANT
“O” RING
PURGE
ORIFICE
INLET
HEATER
PURGE
VALVE
MOUNTING
BRACKET
LOCK
NUT
CHECK
VALVE
“O” RING
“O” RING
SAFETY
VALVE
MOUNTING
BRACKET
OIL
FILTER
RETAINING
RING
EXHAUST
DEFLECTOR
DESICCANT
SEALING
PLATE
INLET
CARTRIDGE
BOLT
DESICCANT
CARTRIDGE
PURGE
VALVE
PISTON
CONTROL
PORT
PURGE
VALVE
OUTLET
LOCK
NUT
SPRING
RETAINER
PERFORATED
PLATE
OIL
FILTER
HEATER
THERMOSTAT
ENCLOSURE
ELECTRICAL
TERMINAL
AD-1™ AIR DRYER
FIGURE 2 - SECTIONAL VIEWS
2
AD-2™ AIR DRYER
The desiccant beads are held in place by steel perforated
plates and filter cloths. The top plate is held in place by a
spring, and the bottom plate rests on a shoulder
approximately 1/8" from the bottom of cartridge housing.
The end cover assembly is retained by a lock ring, cap
screws and retainers and houses the purge valve and heater
assembly if so equipped.
The heater and thermostat assembly prevent freeze-up in
the purge drain valve when the dryer is used in severe winter
conditions. The heater and thermostat assembly is standard
in the AD-2™ air dryer and was optional equipment for the
AD-1™ air dryer. The 12 volt, 60 watt and 24 volt, 60 or 120
watt DC heater and thermostat assembly has an operating
range between 45°F and 85°F.
NOTE: The heater and thermostat assembly provided with
the AD-2™ air dryer has a 3/16" diameter threaded
electrical terminal protected by a boot. The AD-1
air dryer assembly incorporates a #16 gauge lead
wire. Both types are serviceable. The heater and
thermostat assembly should be connected to the
“on” position of the engine control or ignition switch
and protected with the proper size fuse. For details
on installation, please refer to the “Installation”
section.
OPERATION
The operation of the air dryer can best be described by
separating the operation into two cycles; the charge cycle
and the purge cycle.
Charge Cycle (Figure 3) Compressor in Compressing Cycle
- With the compressor in its “loaded” or compressing cycle,
air from the compressor enters the air dryer through the
discharge line. When the air, along with the water and
contaminants, enter the air dryer, the velocity or speed of
the air reduces substantially and much of the entrained liquid
drops to the bottom or sump of the air dryer. The initial air
flow is toward the bottom of the dryer, but air flow direction
changes 180° at the bottom of the air dryer, dropping some
water and oil.
The air now passes through the oil separator filter which
removes oil and foreign material but does not remove water
vapor. At this point, the air remains saturated with water.
The filtered air and vapors penetrate the desiccant drying
bed and the adsorption process begins. Water vapor is
removed from the air by the desiccant.
The unsaturated “dry” air passes through the ball check
valve and purge orifice into the purge volume. From the
purge volume air flows through an outlet check valve, and
into the first reservoir.
NOTE: The AD-1™ air dryer does not incorporate an integral
outlet check valve. The single check valve in an
™
air dryer installation would be located in the
AD-1
line between the AD-1
™
air dryer outlet port and the
first reservoir.
Purge Cycle; (Figure 4) When desired system pressure is
reached, the governor cuts out, pressurizing the unloader
cavity of the compressor which unloads the compressor
(non- compressing cycle). The line connecting the governor
unloader port to the end cover purge valve port (bottom of
the air dryer) is also pressurized, opening the exhaust of
the purge valve to atmosphere. With the exhaust of the
purge valve open, contaminants in the discharge line and
dryer sump are purged, or forced past the open exhaust out
to atmosphere.
The reverse air flows across the desiccant and starts the
removal process of moisture from the desiccant surface.
™
Dry air flowing from the purge volume through the purge
orifice and across the drying bed further dries the desiccant.
The combination of these reverse flows strips the water
vapor from the desiccant (drying bed). This normally takes
between 15-30 seconds.
The desiccant becomes activated from this cycle and is
now ready for another charge cycle, which occurs when the
compressor returns to the compressing cycle. It is for this
reason the air dryer must be purged for 30 seconds, after
receiving moisture saturated air for a maximum of 90
seconds from a 12 CFM compressor.
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.
PREVENTIVE MAINTENANCE AND CHECKING
SERVICEABILITY
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.
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:
3
AD-2™ AIR DRYER OPERATIONAL CHARGE CYCLE
- AIR PRESSURE
FIGURE 3
™
AIR DRYER OPERATIONAL PURGE CYCLE
AD-2
FIGURE 4
4
- AIR PRESSURE
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.
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 “Installation” section.
E. In areas where more than a 30° 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 also that 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 often function adequately.
2. Check mounting bolts for tightness.
3. Check the operation of the integral single check valve
in the AD-2™ air dryer or the “in line” check valve used
with the AD-1™ air dryer. Build the air system to governor
cut-out and observe the test air gauge installed in the
#1 reservoir. A rapid loss of pressure could indicate a
failed check valve. This can be confirmed by checking
at the purge valve exhaust. (Note: Purge valve will be
FIGURE 5
open when governor cut-out pressure is reached. Allow
two minutes for purge cycle before testing the check
valve.)
4. Check for excessive leakage at the purge valve by
coating the exhaust with a soap solution while the
compressor is loaded. (compressing air)
5. 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.
6. Check all lines and fittings leading to and from the air
dryer for leakage and integrity.
7. 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 control “on”, check for
power at the dryer’s electrical terminal (see Figure
16) with a voltmeter or test light. If there is no voltage,
look for a blown fuse, broken wires, or corrosion in
the vehicle wiring harness.
B. Thermostat and Heater
1. Turn off the ignition switch and cool the end cover
assembly to below 40°F. With an ohmmeter check
the resistance between the electrical terminal and
the aluminum of the end cover (see Figure 16).
This resistance should be 2.0 - 4.0 ohms for a
12 volt end cover, 8.1 -13 ohms for a 24 volt, 60
watt cover, and 4.0 - 7.0 ohms for a 24 volt, 120
watt end cover.
2. Warm the end cover assembly to over 90°F. and
check the resistance as above. This resistance
should exceed 1,000 ohms.
If these resistances are within the limits, the
thermostat and heater are operating properly.
If these resistances are outside the limits,
proceed to Step C to determine the cause.
C. Heater Element
With the ignition or engine control switch “off”,
remove the thermostat cover (see Figure 17). With
an ohmmeter check the resistance between the
aluminum of the end cover and the heater post (see
Figure 17). For a 12 volt end cover, the resistance
should be 2.0 - 2.8 ohms. For a 24 volt, 60 watt end
cover, 8.1 - 11.1 ohms, and for a 24 volt, 120 watt
end cover, 4.0 - 4.6 ohms. If the heater resistance
is outside these ranges, a new or remanufactured
end cover should be installed, since the heater
element cannot be serviced.
If the heater resistance is within the limits the
thermostat should be replaced (Kit Number 102637)
or a new or remanufactured end cover installed.
5
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