Pneumatic System 327
Packer Air System
The hydraulic valve, which controls some of the hydraulic functions, is equipped with air actuators
(see Figure 7-1). Each section of the valve has one two-way air actuator. For example, the one that is
on the packer section moves the hydraulic spool inside the valve in either direction, resulting in a
movement of the packer (extension or retraction).
As the packer reaches the end of a stroke, the proximity switch, located behind the packer, sends a
signal to the electronic module to indicate that the packer has reached the end of its stroke. The
multiplex module then operates the air solenoid valve, inside the air valve box, with a 12volt signal
(one signal for packer extend, one signal for packer retract).
When receiving the 12-volt signal (extend or retract) from the module, the air solenoid valve enables
the air pressure to reach the actuator on the main control valve. The spool moves according to the
signal received.
Air Dryer
Some units are equipped with an air dryer and/or alcohol evaporator.
These devices are used to reduce water in the air system, preventing corrosion or freezing of the air
components in cold weather.
Maintenance on the air dryer and/or alcohol evaporator is covered by the chassis manufacturer’s
maintenance manual.
Figure 7-8
Air dryer
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