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Section 180-0022
Suspension System - Levelling Valve
SM 1481 9-98
2
ADJUSTMENT
Numbers in parentheses refer to Fig. 1.
WARNING
To prevent personal injury and property
damage be sure wheel chocks, blocking
materials and lifting equipment are properly
secured and of adequate capacity to do the job
safely.
Checking and Adjusting Ride Height
The height of the air springs determines the ride height.
This is initially set at 175 mm (7 in) and is measured
directly at the air springs, as shown in
Fig. 2. The ride height is adjusted by varying the length
of connecting rod (36) between the levelling valve and
the front suspension frame.
1. Position the unloaded machine on level ground,
apply the parking brake and switch off the engine.
Block all road wheels securely and drain the air from
the primary air tank.
2. Using suitable lifting equipment, raise the front
chassis until the front wheels are just clear of the
ground. Block the chassis in this position.
3. Jack up front suspension frame until a measurement
of 175 mm (7 in) is obtained at the air springs. Refer to
Fig. 2. Control lever (34) should now be in the
horizontal (neutral) position.
DESCRIPTION
The levelling valve is an air operated valve mounted to
a chassis crossmember and attached to the front
suspension frame. Refer to Section 180-0020, FRONT
SUSPENSION.
There are four ports on the valve as follows:
Port 'A' - Inlet from primary air tank
Ports 'B' - Supply ports to air springs
Port 'C' - Exhaust port
OPERATION
Numbers in parentheses refer to Fig. 1.
The purpose of the levelling valve is to control the air
flow to and from the air springs to maintain a constant
air spring stiffness under all load conditions. The valve
control lever (34) is mechanically linked to the
suspension frame by connecting rod (36).
The unloaded height is set by adjusting the length of
connecting rod (36). Air passing through the levelling
valve either deflates the air springs until control lever
(34) assumes a horizontal (neutral) position. In the
horizontal (neutral) position there is no air flow between
the valve and the air springs.
Increasing or decreasing loads alter the height between
the chassis and front suspension frame. This change
is sensed by the levelling valve.
A load increase is sensed by connecting rod (36) which
moves control lever (34) up. This upward movement
permits air to flow from the primary air tank, through
valve housing (18), to the air springs causing the
springs to inflate until control lever (34) reaches its
horizontal (neutral) position. There is no air flow through
valve housing (18) in this position.
A load decrease causes connecting rod (36) to move
control lever (34) downwards. This exhausts air from
the air springs causing them to deflate until control
lever (34) reaches its horizontal (neutral) position.
There is no air flow through valve housing (18) in this
position.
SM - 031
Fig. 2 - Measuring Ride Height
175 mm
(7 in)
Summary of Contents for TA30
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