NMC-WOLLARD 2021Truax Blvd., Eau Claire, WI 54703, Phone (715) 835-3151, Fax (715) 835-6625
M140 Tow Tractor Manual No. 46054
PAGE 1-10
CHAPTER 1 GENERAL INFORMATION AND OPERATING INSTRUCTIONS
1 DESCRIPTION
AUGUST 31, 2008
1.4.22 Steering System
The steering gear is powered by a gimbal-mounted, double-acting hydraulic
cylinder mounted on the front axle. The control unit is actuated directly by the
steering wheel to control ow of hydraulic power to the steering cylinder.
Turning the steering wheel actuates the rotary valve in the power steering
unit. As the valve opens, hydraulic oil travels into a metering motor within the
power steering unit, then out from the motor, through the valve, and out to
the retract side of the steering cylinder. Return oil from the extend side ows
through the valve to the reservoir. Oil owing through the metering motor
causes it to turn, and as it turns, it moves a feedback linkage that returns the
rotary valve to center and locks the steering cylinder in position. The metering
motor therefore ensures that the steering cylinder is precisely controlled by
the command received from the steering wheel.
In the event of a power failure, steering can be done manually by spinning the
steering wheel. In this case, steering wheel movement turns the metering
motor directly through the feedback linkage. The motor is then used as a
pump to force oil into the cylinder, while drawing oil into the suction side
(through check valve) from the return line.
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