The action of hydraulic excavator is complex, and the load changes greatly. In normal operation, the hydraulic system is required to ensure the individual action of each working unit, and make them cooperate with each other to achieve composite action, so as to improve the work efficiency. In traditional hydraulic system, whether quantitative pump or variable pump is used, there is always a part of hydraulic oil overflowing through relief valve, which not only causes great overflow loss, but also causes heating of system and components. The load sensing system (LS) is a regulating system which can control the output power of the pump according to the load demand. In the LS, through the pressure compensation valve and the load sensing pump, the output pressure and flow of the pump can automatically adapt to the load demand, greatly reduce the overflow loss and improve the efficiency of the hydraulic system. However, when the load pressure of each working device is different, and the oil supply flow of the pump is not sufficient, the phenomenon of light load working device "seizing" the hydraulic oil flow of heavy load working device often appears in the load sensing system, which makes the compound action difficult to achieve. Load independent flow distribution system (LUDV) solves the problems existing in load sensing system. In LUDV system, when the pump provides insufficient flow, the working speed of each actuator will be reduced. Because the pressure difference on all valve ports is the same, the proportional relationship between the working speed of each actuator remains unchanged.
