JLG 500RTS ANSI Service Manual - Manual (Page 19)

SECTION 2 - PROCEDURES
3120696 – JLG Sizzor – 2-3
NOTE: Start-up of hydraulic system with oil temperatures
below -15 ° F (-26 ° C). is not recommended. If it is
necessary to start the system in a sub-zero environ-
ment, it will be necessary to heat the oil with a low
density, 100VAC heater to a minimum temperature of
-15 ° F (-26 ° C).
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 -20 °
F (-29 ° C). However, use of this oil will give poor per-
formance at temperatures above 120° F (49° C). Sys-
tems using DTE 11 oil should not be operated at
temperatures above 200° F (94° C). under any con-
dition.
Changing Hydraulic Oil
4. 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.
5. 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.
6. 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 Section 1 for an explanation of the lubricant
key designations appearing in the Lubrication Chart.
2.4 CYLINDERS - THEORY OF OPERATION
1. Cylinders are of the double acting type. The Steer,
Leveling Jack, and Deck Extension systems incor-
porate 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 actu-
ating 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 cylin-
der 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.
NOTE: The Lift cylinder is a single acting cylinder which take
hydraulic pressure to extend and gravity to retract.
2. A holding valve is used in the Lift, and Leveling Jack
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 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.
Relief Valves
Main relief valves are installed at various points within 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