Fault Phenomenon: Atlas truck crane after outriggers are extended and supporting, the vertical cylinder slowly retracts without operation.

Troubleshooting Process:
– Checked hydraulic lock: locking normal.
– Checked cylinder piston seals: seals worn.
– Checked counterbalance valve: spool seal not tight.
– Replaced cylinder seals and counterbalance valve.

Root Cause: The vertical cylinder piston seals wore out, causing internal leakage.

Required Parts: Cylinder seal repair kit, counterbalance valve.