Lull 944E-42 Service Manual - Manual (Page 410)

Hydraulic System
8.158 Model 644E-42/944E-42 Rev. 6/04
8.8.60 Steering Circuit Descriptions
Vehicle steering includes front-wheel steering (see
page 8.114 and page 8.116), four-wheel steering (see
page 8.118 and page 8.120) and crab steering
(see page 8.122 and page 8.124).
a. Front-Wheel Steering
When the Steer Selector Valve (1) is in the
Front-Wheel Steer (CENTER) position (2), the
Front Wheels (3) will steer in the direction the
steering wheel is turned and the Rear Wheels (4)
will remain fixed. 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. Front-Wheel Steering Left Turn (See page 8.114)
In the Front-Wheel Steering Mode, when a LEFT turn is
made, system pressure from the Accumulator Charge/
Secondary Function Valve “CF” Port is applied through
the intake Port “P” of the Power Steering Unit. A specific
amount of hydraulic oil is exhausted from the metering
section and routed to the power steering control valve,
internal to the Power Steering Unit, exiting through Port
“L” where it is channeled through the Steer Selector
Valve Port “R,” exiting through Port “P” and 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” and exiting
through Port “T” to the Main Control Valve, through the Oil
Cooler and then to the Return Filter in the Hydraulic
Reservoir.
2. Front-Wheel Steering Right Turn (See page 8.116)
When a RIGHT turn is made, the Power Steering Unit
spool is shifted so that system pressure from the
Accumulator Charge/Secondary Function Valve “CF”
Port is applied through the intake Port “P” of the Power
Steering Unit. A specific amount of hydraulic oil is
exhausted from the metering section and routed to the
power steering control valve, internal to the Power
Steering Unit, exiting through Port “R” where it 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,” out Port
“R” to the Power Steering Unit Port “L,” exiting Port “T”
and back to the Main Control Valve, through the Oil
Cooler and then to the Return Filter in the Hydraulic
Reservoir.
MU0840
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MT3870