JLG 340AJ Service Manual - Manual (Page 161)

SECTION 5 - HYDRAULICS
3121259 – JLG Lift – 5-3
5.2 HYDRAULIC CYLINDERS
Holding (counterbalance) valves are used in the Lift, Level, Jib,
Telescope, and Axle Lockout circuits to prevent retraction of
the cylinder rod should a hydraulic line rupture or a leak
develop between the cylinder and its’ related holding valve.
NOTE: The steer cylinder weighs approximately 37.2 lbs (16.9 kg).
NOTE: The tower lift cylinder weighs approximately 76 lbs (34.5
kg).
NOTE: The upper lift cylinder weighs approximately 97 lbs (44 kg).
NOTE: The master cylinder weighs approximately 35.3 lbs (16 kg).
NOTE: The level cylinder weighs approximately 37.4 lbs (17 kg).
NOTE: The jib lift cylinder weighs approximately 55 lbs (25 kg).
NOTE: The telescope cylinder weighs approximately 52.7 lbs (23.9
kg).
NOTE: The axle oscillation lockout cylinder weighs approximately
26.2 lbs(11.9 kg).
Disassembly and Assembly Instructions
1. Make sure the work area is large enough for the entire
cylinder and clean and free of dirt. Ensure the cylinder
can be secured firmly in place during disassembly.
2. Prepare all the necessary tools and replacement parts.
Refer to Table 5-2, Required Tools.
General Information
1. Clean any burrs or contamination from the surface of
the cylinder before disassembly.
2. Handle every part with care. Each part is precision made
and hitting parts together or letting them fall could
damage the machined surfaces.
3. Do not twist or strike parts to get them apart. This will
damage the part and/or threads, resulting in leakage
and poor function.
4. Do not let the cylinder in a disassembled condition for a
long period of time. It only takes a short period of time
for the parts to rust.
Standard of Maintenance
Parts and seals should be replaced according to the conditions
as follows.
1. Bushings - 1/4 of the bushing is worn off.
2. Seal and Slide Ring - Replace during disassembly.
3. Pin Bushing - When it is worn down.
4. Rod - Bent or warped more than 0.5mm/1m.
Inspection After Assembly
Table 5-1. Inspection After Assembly
Operation Inspection Without
Load There is no problem when fully extended 5 times without load
Dimension Check the retracted length and stroke
Inspection of the Surface When each of the cylinders are pressurized with test pressure on the piston end, it should not be loose and have no change in pressure or external
leakage
Inspection of external leakage Check the oil leakage at the rod area. Refer to Figure 5-1., Acceptable Oil Leakage on Cylinder Rod.
Inspection of internal leakage Leakage Unit: ml/ 10 minutes
Bore (mm) Leakage (ml) Bore (mm) Leakage (ml) Bore (mm) Leakage (ml) Remark
32 0.4 100 4 160 10
40 0.6 125 5.6 180 12.6
50 1 140 6 200 15.6
63 1.6 220 20
80 2.3 250 22