1. The main pump pressure is low. The excavator uses a double-swash plate axial variable piston pump. Under normal circumstances, the main pump output oil pressure ≥ 30MPa. If the amount of wear between the plunger of the main pump and the cylinder or between the end of the cylinder and the valve plate exceeds the standard (the gap between the plunger and the cylinder should be less than 0.02mm, the difference between the end of the cylinder and the valve plate The contact area should not be less than 90%>, it will cause the output pressure of the main pump to be low, which will be reflected in the mechanical working device, and the phenomenon of weak work of the whole machine will appear.
2. The main pump output flow control valve group is faulty. Then the main pump is always in a small flow state, and the machine will be weak and slow when working.
3. The control pressure output from the pressure reducing valve is low. Under normal circumstances, the pressure reducing valve can reduce and stabilize the output oil pressure of the main pump at 3.3MPa, forming a control oil pressure. If the conical spool on the pressure reducing valve is not closed tightly due to the dirty oil, the output pressure of the pressure reducing valve will be lower than 3.3MPa. At this time, no matter how the operation handle moves, the control oil pressure is always low, and the spool movement of the main control valve of various working devices is small, resulting in a small flow to the working device, resulting in weakness of the machine.
4. The relief pressure of the main relief valve is low. The main relief valve limits the maximum pressure of the entire hydraulic system to 32.5 MPa. For high pressures exceeding this value, the main relief valve will open to relieve pressure to protect the system from damage. If the small hole on the spool of the main relief valve is blocked due to poor oil quality and the spool is normally open, or the set relief pressure of the main relief valve is low, the actual relief pressure will be low, that is, the system The pressure is low.
5. The unloading valve is faulty. When the engine is started and the operating lever is placed in neutral, the main pump output hydraulic oil returns directly to the tank through the unloading valve, and the unloading pressure is 3MPa. If the unloading valve spool is not closed tightly because the oil quality is too dirty, when the machine is working, the output oil of the main pump will pass through the unloading valve to the oil tank, causing the system to not build high pressure.
