1. The main pump pressure is low. The excavator adopts double swashplate axial variable piston pump. Under normal conditions, the output oil pressure of the main pump is ≥ 30MPa. If the wear between the plunger of the main pump and the cylinder block or between the end face of the cylinder block and the port plate exceeds the standard (the gap between the plunger and the cylinder block shall be less than 0.02mm, and the contact area between the end face of the cylinder block and the port plate shall not be less than 90%), the output pressure of the main pump will be low, which will be reflected in the mechanical working device, and the whole machine will be unable to work.
2. The main pump output flow control valve group is faulty. The main pump is always in a small flow state, and the machine will be weak and slow during operation.
3. The control pressure output by the pressure reducing valve is low. Under normal conditions, the pressure reducing valve can reduce and stabilize the output oil pressure of the main pump at 3.3Mpa to form the control oil pressure. If the conical valve core on the pressure reducing valve is not tightly closed due to dirty oil, the output pressure of the pressure reducing valve will be lower than 3.3Mpa. At this time, no matter how the operating handle acts, the control oil pressure is always low, and the movement of the valve core of the main control valve of various working devices is too small, resulting in the small flow to the working device, resulting in the weakness of the whole machine.
4. The overflow pressure of the main overflow valve is low. The main overflow valve limits the maximum pressure of the whole hydraulic system to 32.5mpa. For high pressure exceeding this value, the main overflow valve will open for pressure relief to protect the system from damage. If the small hole on the valve core of the main overflow valve is blocked due to poor oil quality, resulting in the valve core being normally open, or the set overflow pressure of the main overflow valve is low, the actual overflow pressure will be low, that is, the system pressure will be low.
5. The unloading valve is faulty. When the engine is started and the operating lever is placed in neutral, the output hydraulic oil of the main pump directly returns to the oil tank through the unloading valve, and the unloading pressure is 3Mpa. If the valve core of the unloading valve is not tightly closed due to the dirty oil quality, the output oil of the main pump will pass through the unloading valve to the oil tank during machine operation, so that the system cannot establish high pressure.
