Failure Discription : STC500 is slow except for turning.The arm extension pressure is only 8MP, the arm contraction pressure is 20MP, the starting range is 8MP, the falling range is 20MP.

Failure Analyce & Trouble shooting : 1. Control pressure  is too low.   2. Pressure  adjustment error of main valve.   3. Insufficient  travel of main valve stem.   4. Main plunger pump  is damaged.   5.the center rotary  joint internal oil.

Repair Procedure：

1. Adjust the main control pressure (3MP),  and the phenomenon remains unchanged.
2. first adjust the pressure of the main  valve main system and the normal pressure of each secondary overflow valve,  the phenomenon has not changed.
3. Check the travel of the main valve stem.  The backand forth movement of the stem is completely normal and in  position.No lag occurs.
4. Check that the feedback port of the main  oil pump is in normal pressure, directly connect the control line from the  main and penalty to the feedback port of the pump.The attempt to replace the  pump remains the same.
5. Finally, use short pipe connection  directly, avoid the center rotary joint, and return to normal operation, so  as to confirm the internal oil connection

Principle & Expierence Summary : Hydraulic fault can follow the trend of  hydraulic oil circuit step by step check, eliminate the possible fault of  each component, and then the next step judgment.