Fault Phenomenon: JLG aerial work platform after the engine stalls, operating the emergency lowering valve, the platform does not lower, operator trapped.

Troubleshooting Process:
– Checked emergency valve mechanism: valve stem not depressed.
– Checked hydraulic circuit: circuit blocked.
– Checked cylinder back pressure: back pressure too high.
– Checked operation method: operating error.

Root Cause: The emergency lowering valve is mechanically seized or the hydraulic circuit is blocked.

Required Parts: Emergency lowering valve assembly and cleaning.