Fault Phenomenon: Tailift FD25 diesel forklift after the mast is lifted in place, with the engine off, the mast slowly lowers automatically.

Troubleshooting Process:
– Checked multi-way valve spool: spool not fully returned.
– Checked cylinder seals: lift cylinder piston seals failed.
– Checked hydraulic lock: hydraulic lock cone valve not sealing.
– Checked system internal leakage: excessive internal leakage.

Root Cause: Wear of the lift cylinder piston seals causes internal leakage and lowering.

Required Parts: Lift cylinder seal repair kit.