JLG 110HX Service Manual - Manual (Page 28)

SECTION 2 - PROCEDURES
2-4 – JLG Lift – 3120864
A typical control valve consists of the valve body, sliding
spool, and two solenoid assemblies. The spool is
machine fitted in the bore of the valve body. Lands on the
spool divide the bore into various chambers, which, when
the spool is shifted, align with corresponding ports in the
valve body open to common flow. At the same time other
ports would be blocked to flow. The spool is spring-
loaded to center position, therefore when the control is
released, the spool automatically returns to neutral, pro-
hibiting any flow through the circuit.
Manual Hydraulic Control Valves
The manual hydraulic control valves consist of four-way,
multi-position valve sections, each section incorporating a
sliding spool, spring-loaded to neutral or off. Each spool is
attached to a control lever which provides for proportional
control of the selected system function. This proportional
control enables metering of oil flow in accordance with
spool position, affording variable and smooth speed con-
trol capability. Spool movement causes work ports within
the valve to align in a predetermined way, permitting flow
to the selected function, with the opposing work ports
positioned to allow return flow to the hydraulic reservoir.
Proportional Control Valves - Vickers
The Vickers proportional valves provide a power output
matching that required by the load. A small line connected
to a load sensing port feeds load pressure back to a
sequence valve. The sequence valve senses the differ-
ence between the load and pump outlet pressure, and
varies the pump displacement to keep the difference con-
stant. This differential pressure is applied across the
valve’s meter-in spool, with the effect that pump flow is
determined by the degree of spool opening, independent
of load pressure. Return lines are connected together,
simplifying routing of return flow and to help reduce cavi-
tation.
Load sensing lines connect through shuttle valves to feed
the highest load signal back to the sequence valve. Inte-
gral actuator port relief valves, anti-cavitation check
valves, and load check valves are standard.
Relief Valves
Main relief valves are installed at various points with the
hydraulic system to protect associated systems and com-
ponents against excessive pressure. Excessive pressure
can be developed when a cylinder reaches its limit of
travel and the flow of pressurized fluid continues from the
system control. The relief valve provides an alternate path
for the continuing flow from the pump, thus preventing
rupture of the cylinder, hydraulic line or fitting. Complete
failure of the system pump is also avoided by relieving cir-
cuit pressure. The relief valve is installed in the circuit
between the pump outlet (pressure line) and the cylinder
of the circuit, generally as an integral part of the system
valve bank. Relief pressures are set slightly higher than
the load requirement, with the valve diverting excess
pump delivery back to the reservoir when operating pres-
sure of the component is reached.
Crossover Relief Valves
Crossover relief valves are used in circuits where the actu-
ator requires an operating pressure lower than that sup-
plied to the system. When the circuit is activated and the
required pressure at the actuator is developed, the cross-
over relief diverts excess pump flow to the reservoir. Indi-
vidual, integral reliefs are provided for each side of the
circuit.
2.6 BOOM CHAINS
Adjusting Procedures
ENSURE MACHINE IS ON A FIRM AND LEVEL SURFACE.
1. Position boom fully retracted at +5 degrees horizon-
tal, no load in platform.
2. Torque outer mid section extend chain adjuster to 80
Nm.
3. Torque outer mid section retract chain adjuster to 80
Nm.
4. Torque fly section extend chain adjuster to 80 Nm.
5. Torque fly section retract chain adjuster to 80 Nm.
6. Cycle boom (extend at least 2 meters, then retract
fully).
7. Recheck outer mid section extend chain.
8. Recheck outer mid section retract chain.
9. Recheck fly section extend chain.
10. Recheck fly section retract chain.
11. Repeat steps (2) thru (10) if necessary.
12. Check for proper operation of boom.
JLG Industries, Inc. requires a complete boom disassem-
bly, per instructions outlined in Boom Maintenance in this
section, every two years. All boom chains and related
components (i.e., sheaves, pins, sprockets, wear pads,
etc. ) must also be inspected and replaced (as necessary)
during this disassembly.