Air Dryer Operation; Air Dryer - Holiday Navigator 2003 Owner's Manual

Chassis Information
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AIR DRYER

Air Dryer Operation

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Accessory air items are other pneumatically operated items such as the air
horn, step well cover, vacuum generator, etc. The accessory air items operate
only when air tank pressures exceed 65 psi. This is done with pressure protection
valves. Should an accessory air item fail the pressure protection valve (PPV)
reserves the remaining air pressure of 65 psi for braking. This will leave the
motorhome with one air tank fully charged for safety back up.
In another situation, whereby all compressed air has escaped from the rear
air tank, a pneumatic back-up safety valve is installed. This is the safety inversion
valve. The inversion valve senses the absence of rear air tank pressure. In this
case the inversion valve will allow the operator to make a modulated spring
brake application, made in conjunction with the emergency spring brake relay
valve. The inversion valve allows the front air tank pressure to recharge the
rear brake chambers after the modulated spring brake application has been
made. This back-up system implements use of all the brakes, allowing the
operator to bring the vehicle to a safe stop. In case of all compressed air
charge escaping from the front air tank, the operator will still have full use of
the rear brakes.
The air dryer is located underneath the motorhome next to the transmission.
The air dryer removes moisture from the compressed air system. This is
important because if air contains moisture it can freeze and prevent operation
of brakes or other pneumatic operated items.
The air dryer has three functions: cooling, filtering and drying the air going
through the motorhome's air system. If an excessive amount of water is present
when performing the monthly air tank drain service, it may be an indication
that the filter for the air dryer needs to be changed.
During system pressure build-up compressed air passes into the air dryer
where the filter system removes contaminants and passes the air into the drying
stage. Initially, moisture that condenses out collects in the base of the dryer.
Moisture-laden air passes through the desiccant bed in the air dryer cartridge
and is dried. When the compressor unloads, the water is expelled and the dry air
flows back through the dryer, drying the desiccant for the next cycle.
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