Fault Phenomenon: SANY SR285 rotary drilling rig difficult to start, travel motor makes dull sound, brake not released.

Troubleshooting Process:
– Checked brake oil pressure: insufficient pilot pressure.
– Checked brake valve: brake release valve spool stuck.
– Checked brake piston: piston seal swollen and seized.
– Checked spring: brake spring broken and stuck.

Root Cause: The hydraulic release piston seal in the travel motor’s internal brake has aged and swollen, causing the piston to seize and preventing brake release.

Required Parts: Replace travel motor brake piston seal repair kit.