Hydraulic is a term of mechanical industry, mechanical and electrical industry. Hydraulic power transmission can be used, known as hydraulic transmission. Hydraulic pressure can also be used as a control mode called hydraulic control.
Hydraulic transmission is based on liquid as the working medium, the use of liquid pressure to transfer power.
Hydraulic control is a control with pressure liquid as a control signal transmission method. The control system composed of hydraulic technology is called hydraulic control system. Hydraulic control typically includes hydraulic open-loop control and hydraulic closed-loop control. Hydraulic closed-loop control is hydraulic servo control, which constitutes a hydraulic servo system, usually including an electrical hydraulic servo system (electro-hydraulic servo system) and a mechanical hydraulic servo system (mechanical hydraulic servo system, or mechanical hydraulic servo mechanism), etc. [2].
A complete hydraulic system consists of five parts, namely, the energy device, the implementation of the device, the control device, the auxiliary device, the liquid medium. Hydraulic pressure is widely used in industrial and civil industries because of its large transmission power, easy transmission and configuration. The role of the executive components of the hydraulic system (hydraulic cylinders and hydraulic motors) is to convert the pressure energy of the liquid into mechanical energy, so as to obtain the required linear reciprocating motion or rotary motion. The function of the energy device (hydraulic pump) of the hydraulic system is to convert the mechanical energy of the prime mover into the pressure energy of the liquid.