Jlg 40H Service Manual User Manual download pdf (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

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.

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