Fault Phenomenon: XCMG XR460 rotary drilling rig a severe hydraulic shock occurs when the mast approaches the horizontal or vertical limit position.

Troubleshooting Process:
– Checked cushion valve: cushion throttle valve at cylinder end improperly adjusted.
– Checked operation: control handle released too quickly.
– Checked accumulator: accumulator for shock absorption failed.
– Checked oil temperature: low temperature causing high viscosity.

Root Cause: The internal cushion throttle valve of the mast luffing cylinder was misadjusted to too large an opening, failing to generate sufficient back pressure for deceleration at the end of the stroke.

Required Parts: Readjust cushion throttle valve to standard setting.