SECTION 2 - PROCEDURES
3121801 2-3
3. The only exception to the above is to drain and fill the
system with Mobil DTE 11 oil or its equivalent. This will
allow start up at temperatures down to-29°C (-20°F).
However, use of this oil will give poor performance at
temperatures above 49°C (120°F). Systems using DTE 11
oil should not be operated at temperatures above 94°C
(200°F). under any condition.
Changing Hydraulic Oil
1. Use of any of the recommended crankcase or hydraulic
oils eliminates the need for changing the oil on a regular
basis. However, filter elements must be changed after
the first 50 hours of operation and every 300 hours
thereafter. If it is necessary to change the oil, use only
those oils meeting or exceeding the specifications
appearing in this manual. If unable to obtain the same
type of oil supplied with the machine, consult local sup-
plier for assistance in selecting the proper equivalent.
Avoid mixing petroleum and synthetic base oils. JLG
Industries recommends changing the hydraulic oil every
two years.
2. Use every precaution to keep the hydraulic oil clean. If
the oil must be poured from the original container into
another, be sure to clean all possible contaminants from
the service container. Always clean the mesh element of
the filter and replace the cartridge any time the system
oil is changed.
3. While the unit is shut down, a good preventive mainte-
nance measure is to make a thorough inspection of all
hydraulic components, lines, fittings, etc., as well as a
functional check of each system, before placing the
machine back in service.
Lubrication Specifications
Specified lubricants, as recommended by the component
manufacturers, are always the best choice, however, multi-pur-
pose greases usually have the qualities which meet a variety of
single purpose grease requirements. Should any question
arise regarding the use of greases in maintenance stock, con-
sult your local supplier for evaluation.
2.4 CYLINDERS - THEORY OF OPERATION
Cylinders are of the double acting type. The Lift and Steer sys-
tems incorporate double acting cylinders. A double acting cyl-
inder is one that requires oil flow to operate the cylinder rod in
both directions. Directing oil (by actuating the corresponding
control valve to the piston side of the cylinder) forces the pis-
ton to travel toward the rod end of the barrel, extending the
cylinder rod (piston attached to rod). When the oil flow is
stopped, movement of the rod will stop. By directing oil to the
rod side of the cylinder, the piston will be forced in the oppo-
site direction and the cylinder rod will retract.
A holding valve is used in the Lift circuit to prevent retraction
of the cylinder rod should a hydraulic line rupture or a leak
develop between the cylinder and its related control valve.
2.5 VALVES - THEORY OF OPERATION
Solenoid Control Valves (Bang-Bang)
Control valves used are four-way three-position solenoid
valves of the sliding spool design. When a circuit is activated
and the control valve solenoid energizes, the spool is shifted
and the corresponding work port opens to permit oil flow to
the component in the selected circuit, with the opposite work
port opening to reservoir. Once the circuit is deactivated (con-
trol returned to neutral), the valve spool returns to neutral
(center) and oil flow is then directed through the valve body
and returns to reservoir. 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, prohibiting any flow
through the circuit.
Proportional Control Valves
The proportional control 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 difference between the
load and pump outlet pressure, and varies the pump displace-
ment to keep the difference constant. 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
cavitation. Load sensing lines connect through shuttle valves
to feed the highest load signal back to the sequence valve.
Integral actuator port relief valves, anti-cavitation check
valves, and load check valves are standard.
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