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

The function of the power element is to convert 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. Hydraulic pump structure generally has gear pump, vane pump and plunger pump, their performance comparison as shown in 1-1

Actuators (such as cylinders and hydraulic motors) convert the pressure energy of the fluid into mechanical energy to drive the load in linear reciprocating or rotary motion.

Control elements (that is, various hydraulic valves) control and regulate the pressure, flow and direction of the liquid in the hydraulic system. According to the different control functions, hydraulic valve can be divided into pressure control valve, flow control valve and direction control valve. Pressure control valve is divided into flow valve (safety valve), reducing valve, sequence valve, pressure relay, etc. The flow control valve includes throttle valve, adjustment valve, shunt and collecting valve, etc. Directional control valve includes one-way valve, liquid control one-way valve, shuttle valve, reversing valve and so on. According to different control mode, hydraulic valve can be divided into switch type control valve, fixed value control valve and proportional control valve.

Auxiliary components include oil tank, oil filter, oil pipe and connection, sealing ring, pressure gauge, oil level oil thermometer, etc.

Hydraulic oil is the working medium to transfer energy in the hydraulic system. There are various kinds of mineral oil, emulsion and forming hydraulic oil.

Advantages of hydraulic system:

Compared with mechanical and electrical transmission, hydraulic transmission has the following advantages:

1. Various components of hydraulic transmission can be conveniently and flexibly arranged according to requirements.

2. Light weight, small volume, low inertia and fast reaction speed.

3, easy to control, can achieve a wide range of stepless speed regulation (speed regulation range up to 2000:1).

4. It can automatically realize overload protection.

5. Mineral oil is generally used as the working medium, which can be lubricated by itself relative to the moving surface and has a long service life.

6. It's easy to move in a straight line.

7, it is easy to achieve the automation of the machine, when using electro-hydraulic joint control, not only can achieve a higher degree of automatic control process, but also can achieve remote control.