The development of hydraulic technology is closely related to the theoretical research achievements of fluid mechanics and the development of related disciplines such as engineering materials and hydraulic media. In 1650, Pascal proposed Pascal's principle of pressure transmission in a closed, static liquid; in 1686, Newton revealed the law of internal friction of viscous fluids; by the 18th century, two important equations in fluid mechanics—the continuity equation and the Bernoulli energy equation—were established successively. These theoretical achievements laid the theoretical foundation for the development of hydraulic technology.

 

In 1795, the British inventor J. Bramah invented the world's first hydraulic press. He was the first to use water not only for energy transmission but also for control signals, marking the beginning of the engineering application of modern hydraulic technology. The invention of the hydraulic press was also closely related to the emergence of engineering materials such as cast iron and some new manufacturing methods at that time. After W. C. Amst invented the gravity-type accumulator in 1851, the application of hydraulic transmission increased rapidly. By the 1890s, hydraulic transmission had been applied to many industrial sectors, including presses, cranes, winches, packaging machines, and testing machines. Due to the poor lubricity of water and its susceptibility to rust, the rise of electric power transmission once reduced the application of hydraulic transmission. It was not until 1905-1908, when American engineers H. Williams and R. Janney invented an axial piston hydraulic transmission device using oil as the working medium, that the stagnation of hydraulic technology began to improve. In addition, in 1910, H. Shaw developed a radial piston pump using oil as the medium, and H. Vickers invented the pilot-operated relief valve in 1936. The emergence of oil-resistant sealing materials such as nitrile rubber in the 1930s allowed hydraulic transmission to gradually replace hydraulic transmission and develop rapidly.

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During World War II, due to the urgent need for military industry for hydraulic transmission systems and servo mechanisms with fast response, accurate action, and high power to arm various military equipment, various high-pressure components were further developed. After the war In the 1950s, hydraulic technology quickly transitioned to civilian industries, and was widely used in machine tools, construction machinery, shipbuilding machinery, pressure machinery, metallurgical machinery, rolling machinery, agricultural machinery, and the automotive industry. Because servo valves are expensive and have poor anti-pollution capabilities, electro-hydraulic proportional valves, which are cheaper, easier to maintain, and have a certain degree of control accuracy, emerged at the end of the 1960s. Because mineral oil is flammable, in special environments such as high temperatures, open flames, and mines, fire-resistant fluids gradually replaced mineral oil as the working medium for hydraulic systems. After further development over the past half-century, hydraulic technology has become a basic technology that includes transmission, control, and detection, and has a significant impact on the technological progress of modern machinery and equipment. It has been widely used in various industrial sectors. For example, 95% of construction machinery, 90% of CNC machining centers, and over 95% of automated production lines produced abroad use hydraulic transmission. The adoption of hydraulic technology has greatly promoted and ensured the improvement of the quality and level of electromechanical products. The degree of adoption of hydraulic technology has become an important indicator of a country's industrial level, and advanced industrial countries around the world attach great importance to the development of hydraulic technology.

Currently, hydraulic technology has made significant progress in achieving high pressure, high speed, high power, high efficiency, low noise, high reliability, and high integration. There have also been many new achievements in improving proportional control, servo control, developing digital control technology, and mechatronics integration.

With the advancement of science and technology and in order to meet the requirements of the host and enhance its own competitiveness, hydraulic technology continues to develop, some shortcomings are constantly being overcome, and its application range is constantly expanding.

The current main development trends are as follows: :

1) Improve efficiency and reduce energy consumption.

Reduce energy consumption through reducing friction and internal leakage, energy recovery, accumulator application, secondary adjustment of load pressure, flow and power matching, and adaptive control of the hydraulic system using microcomputers.

2) Improve control performance to meet the needs of the development of mechatronics integrated hosts.

This requires the development of low-control-power valves, the development of electro-hydraulic proportional valves suitable for field conditions, remote-controlled multi-way valves, electro-hydraulic servo valves suitable for various operating conditions, low-cost proportional valves, and A/D, D/A conversion is not required, and digital valves that can be easily connected to computer interfaces and easily digitally displayed.

3) Develop integrated, composite, miniaturized, and lightweight components.

With the increasing complexity of hydraulic systems and the increasing requirements for mechatronics integration, hydraulic components are required to have high reliability, reduce piping, reduce pressure loss, improve efficiency, save installation space, and be easy to maintain. To this end, it is necessary to widely develop integrated, composite, miniaturized, and lightweight components. Following integrated block-type stacked valves and plug-in types, in recent years, integrated composite hydraulic devices have emerged that add hydraulic control components to hydraulic actuators or hydraulic systems.

4) Strengthen research and development aimed at improving safety and protecting the environment.

This includes the research, development, and application of water-based fire-resistant media and pollution-free pure water hydraulic technology, noise reduction, improved sealing performance, and reduced leakage.

5) Improve the reliability of hydraulic components and systems.

All countries in the world regard reliability as the primary criterion for selecting hydraulic products. Improving reliability is a systematic project. In addition to relying on scientific design, advanced materials, and perfect processes, attention should also be paid to the reliability of application and maintenance. Conducting research on hydraulic failure mechanism analysis, system status monitoring, fault diagnosis, and reliability prediction, reducing component pollution sensitivity, strengthening pollution control, and applying new engineering materials are all of great significance to improving reliability.

6) Standardization and diversification.

Due to frequent technological innovations, expanding application fields, and shorter product life cycles, it is necessary to continuously develop new components, resulting in an increasing variety of hydraulic components. Due to product diversification, it is not conducive to specialization and is not suitable for traditional mass production methods. In order to resolve the contradiction between diversification and specialization, in the design, standardized design methods that meet the requirements of diversification should be studied, and the minimum number of elements should be fully utilized to achieve multiple varieties through combination. That is, on the basis of standard unit combination, add variable parts to form diversification ; the internal structure remains unchanged, only the connection and installation dimensions are changed; the product processing methods and production systems. To this end, foreign countries widely use production lines composed of numerical control (NC), machining centers (MC), and flexible manufacturing units (FMC) to achieve automated batch production, improve efficiency, and ensure quality.

7) Explore new application fields.

New materials, processes, and working fluids should be widely adopted to improve product performance and reliability, and new components should be developed to meet the special needs of some new application areas. China's hydraulic industry began to develop in the late 1950s. Particularly from the 1980s to the 1990s, the state implemented key reforms in the hydraulic industry and successively introduced nearly fifty foreign technologies, resulting in significant improvements in product level, R&D capabilities, and process equipment levels. Hydraulic technology has been widely applied in various industrial sectors. However, there is a large gap compared with advanced international levels, mainly manifested in: low product level, few varieties and specifications, weak self-development capabilities, poor integration, and particularly insufficient supporting rates for major technical equipment and key projects; unstable product quality, poor reliability, and short lifespan; and a near-total absence of some special components urgently needed in new application areas such as aerospace, marine engineering, biomedical engineering, robotics, micro-machinery, and high-temperature/open-flame environments.

The hydraulic industry has become a bottleneck industry affecting China's machinery industry and expanding international exchanges of electromechanical products. Rapidly changing this backward appearance is an urgent task facing China's hydraulic technology and industrial sectors.