Troubleshooting methods for the automatic retraction of the boom of a mobile tower crane

Based on this analysis, further checks shall be conducted in accordance with the following methods. Extend the boom of the mobile tower crane and load it, keep the operation valve in the middle position, loosen the balance valve to the B-port curved pipe joint, drain the remaining oil until no more oil flows out. Observing the boom of the mobile tower crane, it still continues to retract, while the balance valve continues to discharge without oil, indicating that the balance valve is tightly closed. It is judged that the fault still lies in the hydraulic cylinder.

When disassembling the boom telescopic cylinder again, pull out the piston rod and check that the sealing ring is still intact. After a careful inspection, it was found that there was a fracture in the oil cylinder. This caused the rod cavity and the rodless cavity of the telescopic cylinder to be connected, and the oil passage was also blocked. The principle was the same as that of a seal failure. Therefore, under the action of the load gravity of the boom, the pressure oil in the rodless cavity flowed back to the oil tank through the fracture, causing the boom to automatically retract. After the cracked area was welded firmly, the fault was eliminated.

For the fault of the boom automatically retracting, after ruling out the cause of the balance valve, if no problem can be seen with the seal, the following method can be used for a simple judgment, which is also very accurate.

The piston rod of the telescopic cylinder can be pulled out. Then, the two oil ports leading to the rod cavity should be sealed with paper soaked in hydraulic oil. Then, block one of the two oil ports of the other oil circuit leading to the rod-free cavity with rubber or the like. After that, introduce compressed gas into the other oil port. In this way, if there is a defect in the structural component causing leakage, even if it is a slight leakage, the paper at the two oil ports of the rod-free cavity will be blown away by the gas.