Valve control system is throttling system in essence. In hydraulic excavators, the general three position six way multi way valve is commonly used. The fine adjustment performance and composite operation performance of the slide valve are poor. Since the 1990s, the load sensing control system has been used in hydraulic excavators. The control system is equipped with pressure compensation valve whether it is in the open mode or in the closed mode. Compared with the traditional hydraulic system, the main advantages of the load sensing control system are as follows
(1) Save energy consumption. No matter the constant displacement pump or variable displacement pump is used in the ordinary three position six way directional valve, a part of oil always overflows through the relief valve, which wastes energy. With the load sensing variable system, the flow of the pump is all used on the load, and the pressure of the pump is only 1-3mpa higher than the load pressure.
(2) the flow control accuracy is high, and it is not affected by the load pressure change.
(3) Several actuators can move synchronously or at a certain speed ratio without interference. The common three position six way valve system uses parallel oil circuit. When several actuators act at the same time, the oil output from the pump first flows to the actuator with low pressure and cannot be synchronized. Load sensing control system includes load sensing control valve and load sensing control pump (or quantitative pump).
The full load sensing control system consists of a load sensing control valve and a load sensing control variable pump. The load sensing control valve only solves the fine adjustment performance and composite operation performance of the slide valve, but does not solve the problem of energy saving. The system of constant displacement pump and load sensing control valve also does not save energy consumption, because when the output flow of the pump exceeds the flow required by the actuator (hydraulic cylinder and hydraulic motor), the excess oil flows back to the oil tank through the pressure compensation valve and becomes heat energy. Only full load sensing control system can solve the problem of energy saving.