Slow recovery action of excavator forearm

A user reported thatKobelco SK210LC-6Slow and powerless excavator arm recovery action

Cause analysis:

1. Upon arrival at the scene, it was confirmed that the malfunction occurred: the forearm retrieval action was abnormally slow (7 seconds), and the inability to excavate was true.
2. Preliminary inspection found that: a. When the right operating handle is neutral, the boom descends and there is abnormal movement of the excavator bucket;
b、 When operating the forearm recovery, there is a phenomenon of holding the car. According to the after-sales service diagnosis, the pilot pressure at this time is 1.2M, and the voltage value of the low-pressure sensor is 1.9V.
3. The reason for the abnormal operation of the control working device of the right operating handle when it is in the neutral state mentioned above has been confirmed through inspection to be due to the inability of the plunger springs of the right operating pilot valve to reset normally. After applying for replacement of the right pilot valve assembly, the abnormal operation fault of the control working device of the right operating handle has been resolved when the original right operating handle is neutral.
4. After replacing the pilot valve assembly, the fault of the handle not resetting was resolved. However, the slow and powerless movement of the forearm still exists.
5. Based on the hydraulic schematic diagram and the phenomenon (2-b) mentioned above, further analysis is carried out: a. After ruling out that it is not a fault with the low pressure sensor (circuit) of the forearm, it is suspected that there may be a leak in the pilot oil recovered by the forearm. Therefore, the pilot oil pipe between the second speed solenoid proportional valve of the forearm and the second speed valve core of the forearm is blocked, and the pressure of the second pilot recovered by the forearm changes to 3.8V, 3M.
6. Based on the above inspection results, we preliminarily infer that there is an abnormality in the 2nd speed valve core of the forearm.

Solution:

We used regional inventory machines to inspect the faulty machine by replacing the small arm 2-speed valve core. After replacement, the faulty machine returned to normal use. And after installing the replaced faulty arm 2-speed valve core on the inventory machine, the same fault phenomenon as the faulty machine appeared on the inventory machine, which once again confirmed our previous inference.