Fault Phenomenon: CAT rotary drilling rig a loud impact sound occurs when the mast reaches the luffing limit.

Troubleshooting Process:
– Checked cushion valve: internal cylinder cushion spool stuck.
– Checked piston: cushion plunger worn.
– Checked operation: luffing speed too fast.
– Checked oil quality: contaminated fluid causing spool sticking.

Root Cause: The mechanical cushion valve inside the luffing cylinder failed due to debris, unable to decelerate at the end of the stroke.

Required Parts: Luffing cylinder repair kit or cylinder replacement.