Specifications

Vehicle System System Operation 21
The hydraulic gear pump (18) is driven off the
transmission PTO which draws oil from the
hydraulic oil tank (23). Oil is supplied to the first
control valve (7) section through hydraulic line (21).
This section also contains the priority valve that
distributes oil to the following areas based on, 1st
brakes, 2nd steering, and 3rd implement flow
demand (mast/tilt/auxiliary functions). A constant
flow of 0.8 GPM is provided by the priority valve to
the brake power master cylinder (13). From the
CF port, oil flows through hydraulic line (10) to the
steering unit. From the LS port, oil flows through
hydraulic line (11) to the steering unit. The
remaining oil from the control valve and the power
master cylinder is returned to the hydraulic tank
through hydraulic lines (22).
The safety unloader solenoid of the priority valve
section prevents oil flow through the control valve
when the operator has left the seat thereby
preventing any function regardless of lever position.
Unloader solenoid valve (8) is electrically connected
to the seat switch. The solenoid valve (8) is turned
off within 3 seconds of the operator leaving the seat.
System pressure drops to less than 7 bar (100 PSI)
and oil is diverted to tank instead of flowing through
the control valve. Once the operator returns to the
seat, the solenoid valve is turned on opening oil
flow to the control valve and immediately returning
normal work function to the control valve.
An additional safety lift lock function is also included
which works much the same as the unloader
solenoid mentioned above. This solenoid valve (9)
prevents lowering of the carriage and/or mast when
the operator leaves the seat more then 3 seconds,
or the key switch is off. When the solenoid is off,
oil flow is prevented from exiting the lift cylinders if
the lever is pushed accidentally. Normal operation
returns once the key switch is turned on or the
operator returns to the seat.
A needle valve (16) on the side of the lift section
can be used in an emergency should the lowering
function not work normally. Approximately one
half turn counter-clockwise makes it possible to
lower the mast and/or carriage when the lift spool is
shifted for lowering. After lowering the mast or
carriage to the ground and with the start key off,
inspect for possible causes of the malfunction.
Refer to the detailed trouble shooting guide will be
shown in TESTING and ADJUSTING.
The lift cylinder lowering speed is controlled by a
flow regulator valve integrated into lift spool.
Levers of control valve move spools within the
control valve. The movement of spool allows fluid
for lift, tilt, and side shift (5) functions. The return
hydraulic fluid from each cylinder flows through
control valve, hydraulic line (22), through the filter-
return (20), and back to a hydraulic tank.
If the pressure in the lift circuit goes higher than the
pressure setting shown in the CONTROL VALVE
SECTION of SPECIFICATION, the main relief valve
(15) opens to control system pressure and dump
excess pressure to the hydraulic tank. If the
pressures in the tilt and/or auxiliary circuits go
higher than the pressure setting shown in the
CONTROL VALVE SECTION of SPECIFICATION,
the secondary relief valve (14) opens to control
system pressure and dump excess pressure to the
hydraulic tank.
Flow protectors (2) & (4) integrated in the lift
cylinders provide a controlled decent of the mast
and/or carriage if a critical hydraulic line is broken.
Sudden dropping of the mast and/or carriage is
controlled.
The speed of forward/backward tilt and side shift
cylinder extension are controlled by individually
adjustable flow controls internal to each section of
the control valve. Additionally, the counter-
balance valve (or tilt lock valve) in the tilt spool
prevents cavitations (development of air pocket) in
tilt cylinder. For a complete hydraulic circuit, see
the foldout, in the back of this module.