Main Control Valve / Distributor for Hitachi ZAX870-3 ZAX870-5G ZAX870-5B Excavator Part No 4713089

Symptoms: Weak digging power; performance worsens when hot; boom/arm cylinder sinks.

Cause: Dirty hydraulic oil scratches the spool and valve bore.

Symptoms: Slow boom, arm, bucket, and swing action; poor compound operation.

Cause: Oil contamination, oil sludge, damaged return spring.

Symptoms: Low working pressure, pressure fluctuation, whistling noise.

Cause: Worn valve core, spring fatigue, clogged damping hole.

Symptoms: Oil seepage between valve slices and end covers.

Cause: Aged sealing rings, loose bolts, air suction causing cavitation.

Symptoms: Boom and arm sink slowly, worse under heavy load.

Cause: Contamination or wear on the holding valve sealing surface.

Symptoms: Sudden heavy oil leakage, unable to build hydraulic pressure.

Cause: Long-term pressure impact, uneven bolt tightening torque, casting defects.