Fault Phenomenon: Hitachi ZX330 excavator when digging hard soil, the bucket curl is weak, easily stalls the engine.

Troubleshooting Process:
– Checked relief valve: bucket cylinder overload relief valve setting too low or stuck.
– Checked cylinder: bucket cylinder internal leakage.
– Checked main pump: pump flow insufficient.
– Checked mechanical: bucket linkage deformed.

Root Cause: The bucket cylinder overload relief valve spool is stuck partially open by debris, preventing pressure from reaching the rated value.

Required Parts: Clean or replace bucket overload relief valve.