Hydraulic cylinders have been gradually standardized, serialized, and its specifications, varieties, quality, performance have greatly improved, especially the use of electronic technology, servo technology and other new technology and new technology, the hydraulic system has been significantly improved the quality, It has played a significant role in the national economy and military industry.

From a different perspective, the hydraulic system can be divided into four different forms.

(1) According to the oil circulation, hydraulic system can be divided into open system and closed system. Open system refers to the hydraulic pump oil sucked from the tank, the oil after a variety of control valves, hydraulic actuators, back to the oil through the valve back to the tank. This system structure is relatively simple, you can play the tank heat, sediment impurities, but often due to oil and air contact, so that air can easily penetrate the system, resulting in instability and other consequences of institutions. Open system fuel tank, pump self-priming performance. In the closed system, the oil inlet pipe of the hydraulic pump is directly connected with the oil return pipe of the execution component, and the working liquid is closed and circulated in the pipeline of the system. Its compact structure, less chance of contact with air, the air is not easy to infiltrate the system, so the transmission is relatively stable. The speed change and changeover of the working mechanism are realized by adjusting the variable mechanism of the pump or the motor so as to avoid the hydraulic impact and energy loss that occur during the open system commutation. However, the closed system is more complicated than the open system. Because of no oil tank, the cooling and filtering conditions of the oil are poor. To compensate for leaks in the system, a small flow charge pump and tank are usually required. Due to the single-rod double-acting cylinder size chamber flow range, the work process will make the power use decline, so the closed-system actuators are generally hydraulic motors.

(2) According to the number of hydraulic pumps in the system, it can be divided into single pump system, double pump system and multi-pump system.

(3) according to the hydraulic (hydraulic cylinder) pump used in different forms, can be divided into quantitative pump system and variable pump system. The advantage of variable displacement pump is that it can take full advantage of the power of the engine within the adjustment range, but its structure and manufacturing process are complicated and the cost is high. It can be divided into manual variable, variable control variable, servo variable, pressure compensation variable, constant pressure variable , Hydraulic variables and many other ways.

(4) According to the implementation of different components of the oil supply can be divided into series system and parallel system. In a tandem system, the oil return of the last actuator is the oil into the next actuator, and the pressure is reduced once by one actuator. In a tandem system, when the main pump supplies oil to each actuator controlled by the multi-way valve, the movement of each actuator can be combined as long as the outlet pressure of the hydraulic pump is sufficient. However, due to the pressure of the actuator is superimposed, so to overcome the load capacity will decrease as the number of actuators increases.

Almost all modern engineering machinery used hydraulic system (hydraulic cylinder), and with electronic systems, computer control technology, has become an important part of modern engineering machinery.