May.20,2026
Fault: The boom drops slowly when raised, but drops very fast when supporting the machine, with the chain hitting the ground quickly.
Analysis:
Boom oil seal and piston are new; cylinder barrel and control valve show no visible abnormality.
Swap arm and boom valves; the arm works normally, excluding pilot handle and boom valve issues.
The fault is confirmed to be in the boom cylinder. A hidden groove is found in the middle of the cylinder barrel (not visible by flashlight).
Inspection and Repair:
The groove in the middle of the cylinder barrel does not cause oil leakage at ordinary times.
When supporting the machine, the piston stays at the groove position, causing rapid drop. Repairing this section eliminates the fault.
