A complete hydraulic system consists of five parts, namely, power components, actuators, control components, auxiliary components and hydraulic oil.

The function of the power element is to change the mechanical energy of the prime mover into the pressure energy of the liquid. It refers to the oil pump in the hydraulic system, which provides power to the whole hydraulic system. The structure of hydraulic pumps usually include gear pumps, vane pumps and piston pumps.

The actuating elements (such as hydraulic cylinders and hydraulic motors) are used to convert the pressure energy of the fluid into mechanical energy and to drive the load in linear reciprocating or slewing motion.

Control elements (i.e. hydraulic valves) control and regulate the pressure, flow, and direction of the liquid in the hydraulic system. According to different control functions, the hydraulic valve can be divided into pressure control valve, flow control valve and directional control valve. Pressure control valve is divided into relief valve (An Quanfa), pressure relief valve, sequence valve; flow control valves including throttle valve, regulating valve, diversion valve; directional control valve includes a one-way valve one-way fluid control valve, shuttle valve, reversing valve, etc.. According to different control methods, the hydraulic valve can be divided into switching control valve, fixed value control valve and proportional control valve.

The auxiliary components include oil tank, oil filter, oil pipe and pipe joint, sealing ring, pressure gauge, oil level, oil temperature meter, etc..

Hydraulic oil is the medium of transmission of energy in hydraulic system. There are several kinds of mineral oil, emulsion and synthetic hydraulic oil.

Hydraulic technology uses the Pascal's Law: the pressure on a closed liquid can vary in size and pass in all directions. Then, a small force is applied to a small area of the piston, because the pressure is transmitted, so a greater force is exerted on the larger piston on the other side.