JLG 40H Service Manual - Manual (Page 23)

SECTION 2 - PROCEDURES
3120240 – JLG Lift –
2-3
Hydraulic Oil.
5. Refer to Table 1-1 for recommendations for viscosity
ranges.
6. JLG recommends Mobilfluid 424 hydraulic oil, which
has an SAE viscosity of 10W-30 and a viscosity
index of 152.
NOTE: Start-up of hydraulic system with oil temperatures
below -15° F. is not recommended. 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 minimum temperature of -15° F.
7. 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 -
20°F. However, use of this oil will give poor perfor-
mance at temperatures above 120° F. Systems using
DTE 11 oil should not be operated at temperatures
above 200°F. under any condition.
Changing Hydraulic Oil.
8. 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.
9. 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.
10. 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.
Systems Incorporating Double Acting
Cylinders:
Cylinders are of the double-acting type. Systems incorpo-
rating double-acting cylinders are as follows: Lift, Tele-
scope, Platform Leveling, Steer and Lockout. 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 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 rod will
stop. By directing oil to the rod side of the cylinder, the
piston will be forced in the opposite direction and the cyl-
inder rod will retract.
Holding valves are used in the Lift, Telescope, Slave Level
and lockout 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 consist of the valve body, sliding
s po ol , an d t wo so le no id a ss embl ies . Th e s po ol 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.