Fault Phenomenon: Hitachi ZX330 excavator hydraulic system contamination suddenly increases, filter alarms.

Troubleshooting Process:
– Checked filter base: bypass valve spring broken.
– Checked spool: spool stuck open by debris.
– Checked oil quality: oil extremely dirty.
– Checked pressure differential: no pressure difference across filter.

Root Cause: The hydraulic oil filter base bypass valve spring broke or the spool got stuck open, allowing unfiltered oil to enter the system.

Required Parts: Hydraulic oil filter base repair kit.