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TM 10-3930-664-24
1-17.
HYDRAULIC SYSTEM. (Figure FO-1)
a.
The hydraulic system controls forklift steering and provides the force for operation of the mast assembly.
Hydraulic oil is supplied from a common tank and pressurized by an engine-driven rotary pump. The hydraulic system
consists of the following components:
°
27 gallon hydraulic tank
°
Hydraulic fluid filter
°
Engine-driven rotary pump
°
Priority valve
°
Orbital steering valve
°
Steering selector valve
°
Directional control valve
°
Sideshift cylinder
°
Tilt cylinders (2)
°
Roll cylinder
°
Mainlift cylinders (2)
°
Freelift cylinder
b.
The hydraulic system is equipped with a filter. This filter is designed to remove any fluids or solids
suspended in the oil and prevent contamination of the system. The filter is equipped with a restriction indicator that
indicates decreased flow through the filter due to clogging. Should clogging occur, the filter’s bypass valve will actuate (25
psi) and allow oil to bypass the filter and continue on to system components.
c.
Oil is drawn from the systems hydraulic tank and pressurized by the hydraulic pump. Pressurized oil is
distributed to the steering and mast components by an external pilot-operated priority valve. The priority valve’s rated flow
is 16 gpm with a relief pressure of 1500 psi.
c.
Steering System. The steering system is pressurized by the hydraulic pump and controlled by a power-
assisted steering wheel. Hydraulic oil is drawn from the tank by the pump, passes through the system priority valve, and
onto an orbital steering valve. The steering valve controls the flow of oil to the steering cylinders in response to the
movement of the steering wheel.
d.
A three-position steering selector valve allows the operator to select the steering mode. Forward position
directs hydraulic oil to both the front and rear axles for four-wheel steering. Center position directs oil to only the front axle
for traditional two-wheel steering. Rear position directs oil to both axles for crab steering (allowing movement at an angle
left or right).
e.
Steering cylinders in the front and rear axles control wheel movement. Cylinder rod ends are attached to the
left and right wheel hubs. Cylinder rods turn the wheels left or right in response to steering wheel movement. The
selection of two-wheel steering actuates only the front axle cylinder. Four wheel steering actuates both the front and rear
axle cylinders, directing the rear wheels to turn opposite the direction of the front wheels. Four-wheel crab steering
actuates both cylinders, directing all wheels to turn in the same position.
f.
Mast Assembly. The mast assembly control components are pressurized by the same system hydraulic
pump. The Directional Control Valve located in the driver’s compartment controls the flow of hydraulic oil to the cylinders.
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