Fault Phenomenon: Bauer BG30 rotary drilling rig when suspending a load on the main winch, the wire rope slowly slides down automatically.

Troubleshooting Process:
– Checked counterbalance valve: spool worn or stuck.
– Checked cylinder/motor: actuator internal leakage.
– Checked brake: brake functioning.
– Checked lines: no external leakage.

Root Cause: The main winch counterbalance valve spool is worn, unable to seal completely, causing high-pressure oil to slowly leak and the load to descend.

Required Parts: Clean or replace main winch counterbalance valve.