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4-8 REAR SUSPENSION
Overtravel Lever
Inlet
(Air Inlet Pqsition)
Valve
Lever
Note : Air Pressure Enters
Through Check Valve and
Passes Out Open Inlet
Valve To Bellows
Overtravel Lever
(Neutral-Center Position)
Note : No Movement
of Air Pressure
(All Valves Closed)
Overtravel Lever
(Air Exhaust Position)
Note : Air Pressure From
Bellows Plows Out Exhaust
Valve To Atmosphere
Exhausting
Air Pressure
LOADING
NEUTRAL
UNLOADING
Figure 9-Operation of Height Control Valve
further valve action or air pressure change
takes place until load is increased or de-
creased, moving valve arm out of neutral
position for four seconds or more to actuate
intake valve or exhaust valve .
Unloading
When part of load is removed, air pressure in
bellows lifts frame . Valve arm, linked to axle,
is pulled downward from neutral position . This
applies a force on the delay piston, which
moves it slowly .
The exhaust valve lever
moves with the delay piston . The outer end of
exhaust
valve
lever fits
around stem
of
exhaust valve core .
As soon as lever moves
beyond free-travel range, lever pulls on stem
and opens exhaust valve .
Inlet valve remains
closed .
Compressed air from bellows then
flows through the open exhaust valve and out
exhaust fitting to atmosphere .
As the com-
pressed air is exhausted from bellows, the
frame lowers until overtravel lever and shaft
are again in normal (neutral) position,
movement of compressed air either into or out
of suspension system.
Hydraulic Delaying Action
Operation of delay piston in height control
valve prevents change of bellows air pressure
as a result of momentary road shocks, con
serves air supply, and adds life to valve . The
nylon piston moves inside cylinder containing a
silicone type fluid . A flapper valve on either
end of piston allows displacement of fluid or
acts as a check valve, depending on direction
piston moves. Delay piston is moved by piston
pin that is threaded into overtravel shaft . A 4
to 18 second delay results from the closing of
one valve to the opening of other valve .
Overtravel piston is held against flat side of
overtravel shaft by two springs inside piston .
Piston
keeps
overtravel
shaft
in
proper
position relative to valve arm .
Piston also
allows valve arm to rotate through a complete
circle, if necessary, without damaging parts
inside valve .
Valve Arm Free Travel
With vehicle in motion and frame at normal
ride height, control valve arm and shaft are in
neutral position.
Small irregularities in road
cause slight up and down movement of valve
arm.
Clearances
are
provided
between
operating levers and cores of inlet and exhaust
valves, to permit 1/4-inch up or down move-
ment of valve arm from neutral position
without causing valve action.
This com-
pensates for small road bumps. The bumps are
absorbed by tires and bellows without causing
AIR COMPRESSOR
Compressed air for the system is supplied by
an electric compressor which operates when
the
ignition
key
is
in
the
"ON"
or
"ACCESSORY" position.
It is a demand-type
compressor which will start compressing air
when the pressure in the system drops below
100 psi, and will shut off when the pressure
reaches 120 psi.
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