Fault Phenomenon: Zoomlion ZR280 rotary drilling rig when operating in hard rock, the rotary head speed drops significantly or stalls.

Troubleshooting Process:
– Checked main pump: variable pump displacement insufficient.
– Checked rotary head motor: severe motor internal leakage.
– Checked gearbox: gearbox gears damaged or stuck.
– Checked relief valve: rotary head circuit relief pressure set too low.

Root Cause: The internal valve plate of the rotary head drive hydraulic motor is worn, causing high-pressure oil to leak internally, resulting in insufficient output torque.

Required Parts: Repair or replace rotary head hydraulic motor.