SECTION 2 - PROCEDURES
2-4
– JLG Lift –
3120743
2.4
CYLINDERS - THEORY OF OPERATION.
Systems Incorporating Double Acting
Cylinders.
30 electric - Upper Boom Lift, Lower Boom Lift, and
Steer.
35/n35 electric - Upper Boom Lift, Lower Boom Lift,
Telescope, Slave, Master, Rotator, and Steer.
40/n40/45 electric - Upper Boom Lift, Mid Boom Lift,
Lower Boom Lift, Telescope, Slave, Master, Rotator,
and Steer.
A double acting cylinder is one that requires oil flow to
operate the cylinder rod in both directions. Directing oil
(by actuating the corresponding control valve to the pis-
ton side of the cylinder) forces the piston to travel toward
the rod end of the barrel, extending the cylinder rod (pis-
ton attached to rod). When the oil flow is stopped, move-
ment of the rod will stop. By directing oil to the rod side of
the cylinder, the piston will be forced in the opposite direc-
tion and the cylinder rod will retract.
Holding valves are used in the Lift circuits to prevent
retraction of the cylinder rod should a hydraulic line rup-
ture or leak develop between the cylinder and its related
control valve.
2.5
VALVES - THEORY OF OPERATION.
Control Valves.
30 electric - Control Valve 4640725 this valve controls
Swing, Lower Lift, and Upper Lift.
35/n35 electric - Control Valve 4640843 this valve con-
trols Platform, Telescope, Swing, Lower Lift, and Upper
Lift.
40/n40/45 electric - Control Valve 4640797 this valve
controls Platform, Telescope, Swing, Lower Lift, and
Upper Lift.
It consists of cartridge type valves in an anodized alumi-
num manifold. The cartridge valves provide for control of
flow, volume of flow and pressure in the hydraulic system.
The directional control valves are solenoid operated, three
position, 4-way sliding spool type valves. One valve is pro-
vided for each of the three functions. Energizing one of
the electrical coils on a valve will divert the supply of
hydraulic oil to provide motion of that function in one
direction. Energizing the other coil will divert the oil for
motion in the other direction. When neither coil is ener-
gized, the supply of hydraulic oil is blocked.
Flow control valves in the lift circuits provide for control of
the rate of flow when the oil is flowing out of the cap ends
of the cylinders (the load is being lowered). An adjusting
screw on each cartridge flow control valve allows the rate
of flow (speed) to be adjusted. When oil is flowing into the
cap end of the lift cylinders, an internal check valve feature
allows unrestricted flow.
Pressure relief valves limit the pressure in the swing circuit
and the rod end of each lift cylinder. When the pressure in
one of those circuits reaches the set point of the valve, the
valve opens, allowing enough flow to return to the reser-
voir so that the set pressure is not exceeded. An adjusting
screw on each cartridge relief valve allows the set pres-
sure to be adjusted.
The aluminum manifold provides the passages through
which the hydraulic oil is diverted to provide the desired
movement of the actuators. No moving parts of the valves
slide against the manifold and so it is not subject to wear.
Steer Valve 4640726.
(30/35/n35/40/n40/45 electric)
This valve controls the STEER function. It consists of
screw-in cartridge type valves in an anodized aluminum
manifold. The cartridge valves provide for control of direc-
tion of flow and pressure in the STEER hydraulic circuit.
The directional control valve is a solenoid operated, three
position, 4-way sliding spool type valve. Energizing one of
the electrical coils on the valve will divert the supply of
hydraulic oil to provide steering in one direction. Energiz-
ing the other coil will divert the oil for steering in the other
direction. When neither coil is energized, the supply of
hydraulic oil is blocked.
A pressure relief valve limits the pressure in the steer cir-
cuit. When the pressure reaches the set point of the valve,
the valve opens, allowing enough flow to return to the res-
ervoir so that pressure is not exceeded. An adjusting
screw on the cartridge relief valve allows the set pressure
to be adjusted.
The aluminum manifold provides the passages through
which hydraulic oil is diverted to provide the desired
movement of the steer cylinder. No moving parts of the
valves slide against the manifold and so it is not subject to
any wear.
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