Jlg 40H Service Manual User Manual download pdf (Page 29)

SECTION 2 - PROCEDURES

3120240 – JLG Lift – 2-9

5. If used, remove boom prop from beneath boom,

activate hydraulic system and run cylinder through

one complete cycle to check for leaks.

Cylinders With Dual Counterbalance Valves.

Platform Slave Level Cylinder, Lockout Cylinder

and Extend-A-Reach Level Cylinder.

OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION

ONLY.

1. Using all applicable safety precautions, activate

hydraulic system.

2. When working on the platform slave level cylinder,

stroke platform slave level cylinder forward until plat-

form sits at a 45° angle.

3. Shut down hydraulic system and allow machine to

sit for 10-15 minutes. If machine is equipped with a

bang-bang or proportional control valves, turn IGNI-

TION SWITCH to ON, move control switch or lever

for applicable cylinder in each direction, then turn

IGNITION SWITCH to OFF. If machine is equipped

with hydraulic control valves, move control lever for

applicable cylinder in each direction. This is done to

relieve pressure in the hydraulic lines. Carefully

remove hydraulic hoses from appropriate cylinder

port block.

4. There will be initial weeping of hydraulic fluid which

can be caught in a suitable container. After the initial

discharge, there should not be any further leakage

from the ports. If leakage continues at a rate of 6-8

drops per minute or more, the counterbalance valve

is defective and must be replaced.

5. To check piston seals, carefully remove the counter-

balance valve from the retract port. After initial dis-

charge there should not be any further leakage from

the ports. If leakage occurs at a rate of 6-8 drops per

minute or more, the piston seals are defective and

must be replaced.

6. If no repairs are necessary or when repairs have

been made, replace counterbalance valve and care-

fully connect hydraulic hoses to cylinder port block.

7. If used, remove lifting device from upright or remove

prop from below boom, activate hydraulic system

and run cylinder through one complete cycle to

check for leaks.

2.9 CYLINDER REPAIR.

NOTE: The following are general procedures that apply to

all of the cylinders on this machine. Procedures that

apply to a specific cylinder will be so noted.

Disassembly.

DISASSEMBLY OF THE CYLINDER SHOULD BE PERFORMED ON

A CLEAN WORK SURFACE IN A DIRT FREE WORK AREA.

1. Connect a suitable auxiliary hydraulic power source

to the cylinder port block fitting.

DO NOT FULLY EXTEND CYLINDER TO THE END OF STROKE.

RETRACT CYLINDER SLIGHTLY TO AVOID TRAPPING PRES-

SURE.

2. Operate the hydraulic power source and extend the

cylinder. Shut down and disconnect the power

source. Adequately support the cylinder rod, if appli-

cable.

CYLINDERS WITH DOUBLE HOLDING VALVES. BEFORE REMOV-

ING HOLDING VALVES CRACK BLEEDERS TO RELEASE PRES-

SURE.

3. If applicable, remove the cartridge-type holding

valve and fittings from the cylinder port block. Dis-

card o-rings.

4. Place the cylinder barrel into a suitable holding fix-

ture. Tap around outside of cylinder head retainer

with a suitable hammer to shatter loctite.

5. Using a suitable spanner wrench, loosen the cylin-

der head retainer, if applicable, and/or cylinder head

gland, and remove from cylinder barrel.

6. Attach a suitable pulling device to the cylinder rod

port block end or cylinder rod end, as applicable.

EXTREME CARE SHOULD BE TAKEN WHEN REMOVING THE CYL-

INDER ROD, HEAD, AND PISTON. AVOID PULLING THE ROD OFF-

CENTER, WHICH COULD CAUSE DAMAGE TO THE PISTON AND

CYLINDER BARREL SURFACES.

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