Hydraulic components have gradually achieved standardization, serialization, and transformation, and their specifications, varieties, quality, and performance have been greatly improved. Especially after the use of new technologies and new processes such as electronic technology and servo technology, the quality of the hydraulic system has been significantly improved. It has played an important role in the national economy and military industry.

From different perspectives, the hydraulic system can be divided into different forms.

(1) According to the oil circulation mode, the hydraulic system can be divided into an open system and a closed system. Open system means that the hydraulic pump sucks oil from the oil tank. After the oil passes through various control valves, it drives the hydraulic actuators, and returns the oil to the oil tank through the reversing valve. This kind of system has a relatively simple structure and can play the role of heat dissipation of the fuel tank and precipitation of impurities, but because the oil is often in contact with air, it is easy for air to penetrate the system, resulting in unsteady movement of the mechanism. The open system has a large oil tank and the oil pump has good self-priming performance. In a closed system, the oil inlet pipe of the hydraulic pump is directly connected with the oil return pipe of the actuator, and the working fluid is closed in the system pipeline. Its structure is compact, there is less chance of contact with air, and air is not easy to penetrate the system, so the transmission is relatively stable. The speed change and reversal of the working mechanism are realized by adjusting the variable mechanism of the pump or the motor, which avoids the hydraulic shock and energy loss in the reversing process of the open system. However, the closed system is more complicated than the open system, because there is no oil tank, the oil heat dissipation and filtering conditions are poor. To compensate for leaks in the system, a low-flow charge pump and fuel tank are usually required. Due to the unequal flow rate of the single-rod double-acting oil cylinder, the power utilization will be reduced during the working process, so the actuator in the closed system is generally a hydraulic motor.

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

(3) According to the different types of hydraulic pumps used, it can be divided into fixed pump system and variable pump system. The advantage of the variable pump is that it can make full use of the power of the engine within the adjustment range, but its structure and manufacturing process are complex, and the cost is high. It can be divided into manual variables, control variables as much as possible, servo variables, pressure compensation variables, and constant pressure variables. , Hydraulic variable and other methods.

(4) According to the different ways of supplying oil to the actuators, it can be divided into series system and parallel system. In a tandem system, the oil return of the previous actuator is the oil intake of the next actuator, and the pressure will be reduced once every time it passes through an actuator. In the tandem system, when the main pump supplies oil to the actuators controlled by the multi-way valve, as long as the outlet pressure of the hydraulic pump is sufficient, the movement of the actuators can be combined. But because the pressure of the actuator is superimposed, the capacity to overcome the external load will decrease as the number of actuators increases.

In a parallel system, when a hydraulic pump supplies oil to a group of actuators, the flow into each actuator is only a part of the output flow of the hydraulic pump. The distribution of flow varies with the different external loads on each part. First, it enters the actuator with a smaller external load. Only when the external load on each actuator is equal can it achieve simultaneous action.

The mechanical performance of full hydraulic transmission mainly depends on the performance of the hydraulic system, including the quality of the components used, and whether the basic circuit is appropriate. The performance of the system, in addition to meeting the functional requirements, should be carried out in terms of the efficiency of the hydraulic system, power utilization, speed range and fine-tuning characteristics, vibration and noise, and whether the installation and debugging of the system is convenient and reliable.

Almost all modern construction machinery adopts hydraulic system, and combined with electronic system and computer control technology, it has become an important part of modern construction machinery.