Common Faults & Symptoms
Spool and Valve Bore Wear, Large Internal Leakage
Symptoms: Weak digging power; performance worsens when hot; boom/arm cylinder sinks
Cause: Dirty hydraulic oil scratches spool and valve bore
Spool Stuck, Slow or Jerky Movement
Symptoms: Slow boom, arm, bucket and swing action; compound operation poor
Cause: Oil contamination, oil sludge, damaged return spring
Relief Valve and Pressure Compensator Failure, Insufficient System Pressure
Symptoms: Low working pressure, pressure fluctuation, whistling noise
Cause: Worn valve core, spring fatigue, clogged damping hole
O-ring Damage, External Oil Leakage
Symptoms: Oil seepage between valve slices and end covers
Cause: Aged sealing rings, loose bolts, air suction causing cavitation
Holding Valve Seal Failure, Cylinder Drift
Symptoms: Boom and arm sink slowly, worse under heavy load
Cause: Contamination or wear on holding valve sealing surface
Valve Block Cracking (Rare but Serious)
Symptoms: Sudden heavy oil leakage, unable to build hydraulic pressure
Cause: Long-term pressure impact, uneven bolt tightening torque, casting defects