Fault Phenomenon: Skyjack SJIII 3219 scissor lift aerial work platform after rising, operating the descent handle, the platform is stuck in the high position and cannot descend.

Troubleshooting Process:
– Checked emergency descent valve: manually operating the emergency descent valve, the platform still does not move.
– Checked hydraulic lock: hydraulic lock cone valve stuck.
– Checked mechanical structure: debris stuck between scissor arms.
– Checked hoses: hoses not kinked.

Root Cause: The hydraulic lock (check valve) at the bottom of the hydraulic cylinder is stuck due to debris, preventing the return oil path from opening.

Required Parts: Hydraulic lock assembly or spool cleaning.