Lull 6K Service Manual - Manual (Page 260)

Boom and Transfer
6-10 Service Manual — Models 644B, 6K, 844C, 8K, 1044C, 10K
downstream hydraulic line failure or leakage through the control valves or
fittings. Counterbalance valves prevent movement of the cylinders when
the engine is off, even if the control valve levers are operated.
Counterbalance valves also provide relief valve overpressure protection.
WARNING: Do not remove counterbalance valves from cylinders on the
machine while the cylinder is under load (extended). If a
counterbalance valve must be removed, first retract the
cylinder and remove all hydraulic pressure in the cylinder.
Wear eye protection when removing counterbalance valves.
WARNING: Hydraulic cylinders equipped with counterbalance valves may
have hydraulic pressure stored within the cylinder even after
the cylinder is removed from the machine. If a counterbalance
valve must be removed, do so carefully while wearing eye
protection.
Checking Cylinder Condition
Exposed piston rods can be damaged by impact with hard objects. If the
smooth surface of the rod is marred, the rod seal may be damaged.
Cylinders need to be inspected periodically to check for excessive play at
the cylinder pivot ends. Excessive play is an indication of worn bushings
that will need to be replaced.
Note: When the machine or cylinders are stored, retract the cylinder rods to
protect them.
Cylinder maintenance requires periodic inspection for wear and checks for
leakage.
External Leakage
If a cylinder end cap is leaking or if the cylinder leaks around the rod, the
seals must be replaced.
WARNING: DO NOT use your hand to check for leaks. Use a piece of
cardboard or paper to search for leaks.
Internal Leakage
Leakage past the piston seals inside the cylinder can cause sluggish
movement or settling under load. Piston leakage can be caused by worn
piston seals or scored cylinder walls. Scored cylinder walls may be caused
by hydraulic oil contamination. Check hydraulic cylinders for internal
leakage using the following procedure:
1. Lower the boom to the ground, apply the park brake, retract the
cylinder, and stop the engine.