Lull 944E-42 Service Manual - Manual (Page 412)

Hydraulic System
8.160 Model 644E-42/944E-42 Rev. 6/04
c. Crab Steering Mode
When the Steer Select Valve (1) is in the Crab
Steer (RIGHT) position (2), the front wheels (3)
will steer in the direction the steering wheel is
turned and the rear wheels (4) will steer in the
same direction. Return oil from the Steer Select
Valve and Accumulator Charge/Secondary Function
Valve exits the “Drain” Ports and returns to the Hydraulic
Reservoir unfiltered.
1. Crab Steering Left Turn (See page 8.122)
In the Crab Steering mode, when a LEFT turn is made,
the Power Steering Unit control valve spool is shifted so
that the system pressure from the Accumulator Charge/
Secondary Function Valve “CF” Port is applied to the
intake side of the Power Steering Unit Port “P” metering
section. A specific amount of hydraulic oil is exhausted
from the metering section and routed back to the power
steering control valve, internal to the Power Steering Unit,
where it is channeled from Port “L” through the Steer
Selector Valve Port “R,” exiting Port “1” flowing to the
RIGHT rod end of the Rear Steering Cylinder.
Oil from the Left rod end of the Rear Steering Cylinder
flows through the Steer Selector Valve Port “2,” exiting
Port “P” to the LEFT rod end of the Front Steering
Cylinder.
Oil from the RIGHT rod end of the Front Steering Cylinder
flows to the Power Steering Unit Port “R,” exiting Port “T”
flowing to the Main Control Valve, exiting the “Outlet” Port
and passing through the Oil Cooler and then to the Return
Filter in the Hydraulic Reservoir.
2. Crab Steering Right Turn (See page 8.124)
In the Crab Steering mode, when a RIGHT turn is made,
the Power Steering Unit control valve spool is shifted so
that the system pressure from the Accumulator Charge/
Secondary Function Valve “CF” Port is applied to the
intake side of the Power Steering Unit Port “P” metering
section.
A specific amount of hydraulic oil is exhausted from the
metering section and routed back to the power steering
control valve, internal to the Power Steering Unit, where
it is exits Port “R” and is channeled to the RIGHT rod end
of the Front Steering Cylinder.
Oil from the LEFT rod end of the Front Steering Cylinder
flows through the Steer Selector Valve Port “P,” exits Port
“2” and applies pressure to the LEFT rod end of the Rear
Steering Cylinder. Oil from the RIGHT rod end of the Rear
Steering Cylinder flows through the Steer Selector Valve
Port “1,” exiting Port “R” to the Power Steering Unit Port
“L,” exiting Port “T” to the Main Control Valve, exiting the
“Outlet” Port and passing through the Oil Cooler and then
to the Return Filter in the Hydraulic Reservoir.
MU0860
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MT3890