Double Check Valve
When the brake pedal is pushed and the emergency
brake control valve is pushed in (OFF position), there is
no pressure air at inlet passage (1). Air pressure from
the brake control valve causes shuttle (2) to move to the
right and air pressure goes to the air chamber of the
tractor wheel brake. This causes the wheel (service)
brakes to activate. When the brake pedal is released
and the emergency brake control valve is pulled out (ON
position), there is no air pressure at inlet passage (3).
Air pressure from the emergency pilot valve causes
shuttle (2) to move to the left and air pressure again
goes to the air chambers of the tractor and scraper
wheel brakes. This causes the wheel (emergency)
brakes to activate.
DOUBLE CHECK VALVE
1. Inlet passage from emergency pilot valve. 2.
Shuttle. 3. Inlet passage from brake control valve. 4.
Outlet to air chambers.
Air Dryer (Models 613BSNS1 and 613BSS1)
The air dryer is used to remove moisture and foreign
material from the compressed air before it gets to the air
reservoir. Clean dry air is very important for safe
operation and performance of brake systems that use
com-pressed air. Clean dry air will also prevent corrosion
Desiccant beads are used to make the drying bed.
The desiccant beads are of a material that cleans and
makes the air dry. Each bead has a large number of
submicroscopic cavities. Each desiccant bead absorbs
or collects moisture and other foreign material from the
The air dryer is installed in the vertical position in the
air line between the air compressor and the first air
reservoir. The dryer will help reduce corrosion and
prevent possible problems in the air system, especially
the air brake system caused by moisture in temperatures
below 32°F (0°C).
With the use of an air dryer, it is not necessary to
drain the air system reservoirs daily. The desiccant
cartridge and the paper oil filter are removable and must
be replaced at regular service intervals. The cartridge
housing is used to hold the desiccant beads. The
cartridge housing has a plate with holes in it on each
end. There is a filter cloth under each plate. The top
plate is held in place by a spring and the bottom plate is
held by a shoulder near the bottom of the cartridge
housing. A long bolt is used through the center of the
assembled cartridge to hold it in place in the air dryer.
The end cover assembly is held to the bottom of the air
dryer by a lock ring, bolts and retainers. The purge valve
and heater assembly are in the cover assembly. The
heater and thermostat assembly keeps moisture from
freezing in the purge valve drain when the air dryer is
used in temperatures of 320F (0°C) or lower. The 60
watt, 24 volt DC heater and thermostat assembly has an
operating range between 500F (10°C) and 850F (300C).
The operation of the air dryer is given in two parts, the
charge cycle and the purge cycle.
With the air compressor in its "loaded" or
compressing cycle, air under pressure is sent to the air
dryer from the air compressor through air supply line (1).
When the air enters the Air Dryer, the velocity (speed) of
the air goes down and cools. Much of the oil and water in
the air drops into the sump (12). The direction of the air
flow is to the bottom of the Air Dryer where its direction is
reversed and more water and oil go into the sump. The
air now goes through the oil filter ( II) and some oil and
foreign material is removed, but the water vapor is not
removed. At this point, the air is still saturated (full) of
The filtered air and vapors go up into the bottom of
the desiccant drying bed of the desiccant cartridge (10)
and the adsorption procedure begins. Water vapor is
removed from the air by the desiccant.
The unsaturated "dry air" goes through the check valve
(7) and purge orifice (8) into the purge volume (2). From
the purge volume (2) the air goes through check valve
(6), through line (5) to the air reservoir.