Hydraulic pressure is a kind of transmission mode which uses liquid as working medium and uses the pressure energy of liquid to transmit power. A complete hydraulic system consists of five parts, namely, energy device, executive device, control and adjustment device, auxiliary device and liquid medium.

The function of the executive components of the hydraulic system (hydraulic cylinder and hydraulic motor) is to convert the pressure energy of liquid into mechanical energy, so as to obtain the required linear reciprocating motion or rotary motion. Hydraulic pressure has been widely used in industrial and civil industries because of its characteristics of large transmission power and easy transmission and configuration.

A complete hydraulic system consists of five parts, namely, power element, executive element, control element, auxiliary element and working medium.

The function of the power element is to convert the mechanical energy of the prime mover into the pressure energy of the liquid. Power element refers to the hydraulic pump in the hydraulic system, which provides power for the whole hydraulic system. The structural forms of hydraulic pump generally include gear pump, vane pump, plunger pump and screw pump.