PISTON A. 2B3121 - Caterpillar

The boom raise cylinder and boom retract cylinders are equipped with automatic lock valves which are held in the closed position by spring force. In normal operation the valves are opened by pilot oil pressure to release oil from the cylinders when the boom is being lowered or retracted.The boom can be lowered and retracted manually if there is a loss of hydraulic power.
The is no working clearance between the boom and frame when the boom is lowered. Working in this area could result in personal injury or death. Do not approach or work in this area until the boom is properly supported.
Before opening the lock valves manually the machine boom must be supported by a suitable stand or packing capable of supporting the full weight of the boom and attachment, and the load if any. If the boom is close to the horizontal position it will be necessary to use a portable winch or another machine to push the boom to the retracted position.1. Ensure that the machine is stable and will not become unstable as the boom is retracted or lowered. Block the machine if necessary.2. Clear all personnel away from the machine. 3. If the boom is raised, install a suitable stand or packing under number one boom section, and lifting equipment on the boom head. Ensure the full weight is supported. The lifting equipment should be capable of moving to accommodate the change in position of the boom as it is retracted and lowered.
Lowering a raised boom further increases the outreach of the load. This can reduce the forward stability of the machine resulting in machine tip over.This can cause injury or death to the operator or other personnel in the work area.Always retract the boom before lowering it.
4. Loosen locknut (1) on the boom retract lock valve turn screw (2) fully clockwise.5. Slowly lower and adjust the position of the lifting equipment until the boom is fully retracted. 6. If the boom is raised, loosen locknut (3) on the boom raise lock valve and turn screw (4) fully clockwise.7. Ensure the weight of the boom is supported on the lifting equipment and remove the stand or packing.8. Slowly lower and adjust the position of the lifting equipment until the boom is fully lowered.9. Turn screws (2) and (4) fully counter clockwise and then turn each screw clockwise, three quarters of a turn.10. Tighten locknuts (1) and (3).If the boom is lowered, or lowered and retracted using the above the procedure, the boom must be fully raised and lowered and fully extended and retracted several times before the machine is returned to service. This is to ensure that any air which may have entered the boom hydraulic system is purged.