During the operation of a D65EX-12 bulldozer, the blade was unable to cut the soil. The blade could be raised and lowered, but the body could not be raised after it was lowered to the ground. The maintenance engineer found on the spot: The steering and working device hydraulic system of the machine is a load sensing hydraulic system composed of a variable plunger pump, a main control valve and a hydraulic oil tank, and the variable plunger pump is equipped with an LS valve. The high-pressure oil returns to the LS valve of the plunger pump through LS to control the output flow of the variable plunger pump. When the valve stem is inactive, the load sensing pressure is zero. The system relies on the LS valve of the pump to adjust the pump swash plate angle to Maximum, when the system pressure reaches 3.4MPa, it will directly return to the tank through the corresponding unloading valve.

　　Since the steering function is good (pressure up to 37.2MPa), it can be determined that the pump is not damaged, and the reason for the weak cutting of the blade may be: 1: the pilot valve of the working device is damaged, 2: the main valve stem is abnormally worn and causes leakage, 3: LS The safety valve is improperly adjusted or damaged. 4: The pressure compensation valve or the supplement valve is damaged.

　　Continue to check in order, first test the steering pilot valve, the function is normal, the main valve of the working device is disassembled, and there is no abnormal wear. The pressure of the working device safety valve is only 3.1MPa, which should be 20.6Mpa, and then disassemble the pressure compensation valve and the fill valve. There was no abnormal wear and damage. Further inspection showed that the throttle valve was damaged. The working pressure oil leaked seriously through the throttle valve, and there was no normal pressure.