L4-10 Steering Circuit L04037
No Steer, External Shock Load
(Refer to Figure 4-6):
When the operator is not turning the steering wheel,
the steering control unit valve supply is closed. The
directional valve remains centered by its springs thus
closing the passages to ports CL and CR. This cre-
ates a hydraulic lock on the steering cylinders to pre-
vent their movement. If the tires hit an obstruction to
cause a large shock load to force the wheels to the
left, increased pressure will occur in the ends of the
cylinders connected to port CR. The shock and suc-
tion relief valve inside the flow amplifier assembly at
port CR will open at its adjusted setting (2900 psi, (19
995 kPa)) and allow oil to escape from the pressur-
ized ends of the cylinders preventing a higher pres-
sure.
As the cylinders are allowed to move, the other ends
will have less than atmospheric pressure on port CL.
This low pressure permits oil that is escaping through
the CR port relief valve to flow through the check
valve portion of the shock and suction relief valve
connected to port CL. The oil then flows to the low
pressure ends of the cylinders to keep the cylinders
full of oil and prevent cavitation. A shock load in the
opposite direction merely reverses the above proce-
dure.
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