Section E - Hydraulics
Operation Description
Neutral Circuits
E - 12 E - 12
9803-9450-2
Loader Circuit
The standard servo loader valve block consists of two
hydraulic servo operated spools controlling loader arm lift
and carriage tilt functions and a third servo operated
attachments spool which is controlled via a proportional
solenoid valve. A main relief valve controls the maximum
pressure generated in the loader circuits.
When no service is selected the oil passes straight through
the neutral gallery of the valve block. When a service is
selected the neutral gallery is blocked by the selected
spool and oil is directed past the load hold check valve and
onto the ram to operate the service. Return oil from the ram
is fed back through the spool into the valve block exhaust
gallery and back to tank.
An electrically operated servo cut-off valve is fitted in the
servo feed circuit. This is operated by the isolator switch to
allow spool movement only when the switch is closed, i.e.
when the isolator bar is lowered.
A self level valve, fitted as an option, diverts a small
amount of oil to the carriage tilt ram to give self levelling as
the loader arm is raised. The valve is electrically controlled
and can be switched on or off by the operator.
Machines with manual loader controls are as described
above except that the loader valve block consists of two
mechanically operated spools controlling loader arm lift
and carriage tilt functions and a third servo operated
attachments spool which is controlled via a proportional
solenoid valve. The manually operated spools have
electrically operated spool locks.
Transmission Circuit
The transmission pump consists of two axial piston pumps
mounted in-line and driven through a flexible coupling from
the back of the engine. The first pump unit P1 supplies oil
to the left hand motor M1 and the second pump unit P2
supplies the right hand motor M2. The swash plates are
operated by hydraulic servos which are controlled by the
drive joystick. The pump units are controlled independently
to allow the machine to be steered. Relief valves are fitted
in each motor line to prevent excess pressures being
generated in the motor circuits. The charge circuit,
supplied by the charge pump, maintains oil flow through
the pump casing and ensures adequate oil supply to the
pump units during start-up. The motors are cooled by oil
fed through the casings which is then returned to tank T.
Refer to detailed description of the drive circuit.
Servo Circuits
The oil supply to the joystick controllers is fed from the
charge pump, the pressure being governed by the charge
pressure relief valve. The loader joystick feeds servo oil to
operate the spools in the loader control valve. The
transmission joystick feeds oil to the pump servos to
control the machine travel.
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