Drift down / Creep down: The platform slowly descends by its own weight after lifting and stopping, without activating the lowering control. Root cause: Internal leakage in pressure holding circuit. Main failure points:
Internal leakage of hydraulic lock (pilot operated check valve): dirt or scratch on sealing cone, weak return spring. Heavier load causes faster drifting. No external oil leakage.
Cylinder piston seal damage: oil crosses from cap side to rod side inside cylinder. Hidden internal bypass, no visible oil leak outside. Lifting capacity may become weak under full load.
Spool seal wear of lowering solenoid valve, debris stuck on valve seat, slight leakage at neutral position.
External oil leakage: worn rod seal, failed O-rings on fittings, oil seeps out to surface. Contributing factors: high oil temperature, contaminated hydraulic oil. Safety warning: Stop operation immediately. Install mechanical safety supports under platform. Do not work under platform before repair.
