JLG 120HX Service Manual - Manual (Page 25)

SECTION 2 - PROCEDURES
3120819 – JLG Lift – 2-3
Hydraulic Oil
1. Refer to Table 1-1 for recommendations for viscosity
ranges.
2. JLG recommends Kendall Hyken 052 hydraulic oil,
which has an SAE viscosity of 10W-20 and a viscos-
ity index of 152 or Mobilfluid 424 hydraulic oil, which
has an SAE viscosity of 10W-30 and a viscosity
index of 152. Kendall Hyken 052 and Mobilfluid 424
are fully compatible, and can be mixed as neces-
sary.
NOTE: Start-up of hydraulic system with oil temperatures
below -26 degrees C (-15 degrees F). is not recom-
mended. If it is necessary to start the system in a
sub-zero environment, it will be necessary to heat
the oil with a low density, 100VAC heater to a mini-
mum temperature of -26 degrees C (-15 degrees F).
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
degrees C (-20 degrees F). However, use of this oil
will give poor performance at temperatures above
49 degrees C (120 degrees F). Systems using DTE
11 oil should not be operated at temperatures above
94 degrees C (200 degrees 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 40 hours of operation and
every 250 hours thereafter. If it is necessary to
change the oil, use only those oils meeting or
exceeding the specifications appearing in this man-
ual. If unable to obtain the same type of oil supplied
with the machine, consult local supplier for assis-
tance in selecting the proper equivalent. Avoid mix-
ing petroleum and synthetic base oils. JLG
Industries recommends changing the hydraulic oil
annually.
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 contami-
nants 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 main-
tenance 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-purpose 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, consult your local supplier for evalua-
tion. Refer to Table 1-2 for an explanation of the lubricant
key designations appearing in the Lubrication Chart.
2.4 CYLINDERS - THEORY OF OPERATION
Cylinders are of the double acting type. Systems incorpo-
rating double acting cylinders are as follows: Lift, Tele-
scope, Steer, Master Level, Slave Level, Frame Lift, Axle
Extend and Extend-A-Reach. A double acting cylinder is
one that requires oil flow to operate the cylinder rod in
both directions. Directing oil (by actuating the corre-
sponding control valve to the piston side of the cylinder)
forces the piston 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 opposite direction and the cylinder rod
will retract.
Holding valves are used in the Lift, Platform Level, Tele-
scope, and Extend-A-Reach circuits 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 acti-
vated and the control valve solenoid energizes, the spool
is shifted and the corresponding work port opens to per-
mit oil flow to the component in the selected circuit, with
the opposite work port opening to reservoir. Once the cir-
cuit is deactivated (control 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, pro-
hibiting any flow through the circuit.