A 20t crawler excavator was found to have the boom falling automatically. Other causes that may cause the boom to fall automatically are eliminated. In fact, most of them are caused by the failure of the boom reversing valve or its lower chamber overflow valve, which causes the boom to slide automatically. For example, the reversing valve has internal leakage, is not in place, is not closed tightly or is jammed. The overflow valve is not closed tightly and the spring force is weakened, which may cause the fault. Confirm the cause of the fault, and repair or replace the boom reversing valve and the lower chamber overflow valve according to the specific situation to solve the fault. Because precision parts are involved in the disassembly process. So we should not only use professional tools, but also remember the disassembly sequence. In order to avoid wrong sequence during reassembly.
