®
Bendix® AD-1™ and AD-2™ Air Dryers
AD-1™ AIR DRYER
FIGURE 1
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.
SD-08-2403
AD-2™ 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.
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.
5-1/2”
PURGE
VOLUME
PURGE
ORIFICE
19-1/2”
INLET
DESICCANT
“O” RING
HEATER
PURGE
VALVE
OUTLET
MOUNTING
BRACKET
LOCK
NUT
CHECK DESICCANT VALVE SEALING
PLATE
“O” RING
“O” RING
INLET
SAFETY
VALVE
CARTRIDGE
BOLT
MOUNTING
BRACKET
DESICCANT
CARTRIDGE
OIL
FILTER
PURGE
RETAINING VALVE
RING PISTON
CONTROL
PORT
PURGE EXHAUST VALVE
DEFLECTOR
CHECK
VALVE
OUTLET
LOCK
NUT
SPRING
RETAINER
PERFORATED
PLATE
OIL
FILTER
HEATER
THERMOSTAT
ENCLOSURE
ELECTRICAL
TERMINAL
AD-1™ AIR DRYER |
AD-2™ AIR DRYER |
FIGURE 2 - SECTIONAL VIEWS
2
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 AD-1™ air dryer installation would be located in the 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
(noncompressing 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
AD-2™ AIR DRYER OPERATIONAL PURGE CYCLE
- AIR PRESSURE
FIGURE 4
4
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
Loading...