Failure analysis of EX400-5 excavator in both working and walking

A Hitachi EX400-5 excavator to replace the hydraulic oil in the operation of the whole machine and the 6000h after the sudden boom and bucket rod work is slow and weak, not on the right track fault. After examination, the engine works normally, the hydraulic system is no noise, no leakage and leakage, the track tension is also appropriate.

According to the fault phenomenon, the possible faults in the preliminary diagnosis are: No. 2 pump and its overflow valve, center swivel joint, running motor and pilot system.

As a result, the pressure of the pump No. 2 and the pressure of the pilot system are tested first, and all the results are normal, thus eliminating the possibility of the malfunction of No. 2 pump and its overflow valve. In order to avoid blind disassembly, bottom plug plug, truncated rotary joint rotary joint to the walking motor circuit, the test pressure is normal, eliminates leakage fault and oil leakage of the rotary joint. In order to judge whether the running motor has any faults, the pipe of the left and right rotary motors is switched on at the central rotating joint, and the machine is right to walk normally. This eliminates the possibility of a malfunction of the running motor.

Through the above inspection, the No. 2 relief valve, the central rotary joint and the running motor have been eliminated, and the fault point has been concentrated on the No. 2 pump. Due to its normal pressure, the cause of the failure is likely to be on its displacement. Through the transposition test, it is proved that the fault point is on the pump regulator.

Upon examination, it was found that a tiny sheet of metal chip falling from the spring of the reversing valve clamped the valve column and sleeve into one, so that the pump governor lost its regulating function and stuck it to the minimum displacement. After cleaning and loading, the trouble is eliminated.