No Steer, External Shock Load
(Refer to Figure 4-9):
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
creates a hydraulic lock on the steering cylinders to
prevent 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 suction relief valve inside the flow
amplifier assembly at port “CR” will open at its adjusted
setting (3100 psi (21.4 MPa) and allow oil to escape
from the pressurized ends of the cylinders, preventing
a higher pressure.
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 oppo-
site direction merely reverses the above procedure.
L4-14 Steering Circuit L04031
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