The function of the hydraulic system is to increase the force by changing the pressure. A complete hydraulic system consists of five parts: power elements, actuating element, control elements, auxiliary components (accessories) and hydraulic oil. The hydraulic system can be divided into two types: hydraulic transmission system and hydraulic control system. The main function of the hydraulic transmission system is to transmit power and motion. The hydraulic control system should make the output of the hydraulic system meet the specific performance requirements (especially dynamic performance), usually the hydraulic system refers to the hydraulic transmission system.
The function of the power element is to transform the mechanical energy of the prime mover into the pressure energy of the liquid, which means the oil pump in the hydraulic system, and it provides power to the whole hydraulic system. The structural forms of hydraulic pumps are gear pumps, vane pumps, plunger pumps and screw pumps.
The functions of executive elements, such as hydraulic cylinders and hydraulic motors, are to convert the pressure energy of the liquid into mechanical energy, and to drive the load in straight reciprocating motion or rotary motion.
Control components (i.e. 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 valves can be divided into pressure control valves, flow control valves and directional control valves. The pressure control valves include the relief valve (An Quanfa), the pressure relief valve, the order valve, the pressure relay and so on; the flow control valves include the throttle valve, the adjusting valve and the shunting valve, and the direction control valves include the one-way valve, the liquid controlled one-way valve, the shuttle valve, the reversing valve and so on. According to different control modes, hydraulic valves can be divided into switch control valves, fixed value control valves and proportional control valves.
Auxiliary components include oil tank, oil filter, cooler, heater, accumulator, oil pipe and pipe joint, seal ring, quick change joint, high pressure ball valve, hose assembly, pressure gauge, pressure meter, oil level meter, oil thermometer, etc.
Hydraulic oil is the working medium for transmitting energy in the hydraulic system, and there are several kinds of mineral oil, emulsion and synthetic hydraulic oil.