Fault Phenomenon: Zoomlion ZR280 rotary drilling rig when using the auxiliary winch free fall function, the lowering speed is uncontrollable, extremely dangerous.

Troubleshooting Process:
– Checked clutch: free fall pneumatic/hydraulic clutch does not disengage fully or engages too slowly.
– Checked brake: brake release delayed.
– Checked control valve: valve controlling clutch spool stuck.
– Checked air/hydraulic circuit: pressure builds too quickly.

Root Cause: The pilot valve controlling the free fall clutch spool is stuck at maximum opening, causing the clutch to engage instantaneously, losing smooth transition.

Required Parts: Clean or replace free fall control valve.