The history of hydraulic control technology can be traced back to 240 BC. An ancient Egyptian invented the first hydraulic servo system in human history-the water clock. However, in the long historical stage, the hydraulic control technology remained stagnant until the end of 18 and the beginning of 19. On the eve of World War II, with the needs of industrial development, hydraulic control technology has developed by leaps and bounds, and many early control valve principles and patents are the products of this era. For example, Ascani Asia Control Valve Company and Ascani Asia-Walker invented and applied for the patent of jet pipe valve principle. Similarly, Foxboro applied for a patent for the principle of nozzle flapper valve. Siemens Company of Germany invented a dual-input valve with permanent magnet motor and receiving mechanical and electrical signals, which was creatively applied in aviation field.
At the end of World War II, the servo valve is a single-stage open-loop control valve, and the solenoid directly drives the spool to move. However, with the maturity of control theory and the need of military application, great achievements have been made in the research and development of servo valve. 1946, Tinsiey of the United Kingdom obtained the patent of the secondary valve; Raytheon and Bell Airlines invented a two-stage valve with feedback; MIT uses torque motor instead of solenoid, which makes the motor consume less power and have better linearity. 1950, W.C.Moog was the first to invent a single nozzle two-stage servo valve. From 1953 to 1955, T.H. Carson invented the mechanical feedback two-stage servo valve; W.C.Moog invented a two-stage servo valve with two nozzles; Walpin invented the dry torque motor, which eliminated the reliability problem caused by oil pollution of the original torque motor immersed in oil. 1957 R.Atchley developed a two-stage jet tube servo valve based on Askania jet tube principle. 1959 developed a three-stage electric feedback servo valve.
1February, 959, a foreign hydraulic and pneumatic magazine reported the situation of servo valves at that time on page 12, which shows the vigorous development of servo valves at that time. At that time, there were more than 20 manufacturers producing various types of servo valves. In order to compete for the dominant position of servo valve production, various manufacturers have launched fierce competition. Looking back at history, we can see that several manufacturers finally won, and most of them produced two-stage servo valves with feedback and torque motors. We can see that the servo valve of 1960 has many characteristics of modern servo valve. For example, the feedback from the second stage to the first stage forms closed-loop control; Adopt dry torque motor; The pressure recovery from the front stage to the power stage can usually reach 50%; The mechanical symmetry structure of the first stage reduces the influence of temperature and pressure changes on the zero position. At the same time, the direct-acting two-stage closed-loop control servo valve developed from the early direct-acting open-loop control valve also appeared. At that time, servo valves were mainly used in the military field. With the advent of the space age, servo valves have been widely used in the space field, and cutting-edge products such as high-reliability redundant servo valves have been developed.
At the same time, with the continuous expansion of the industrial application of servo valves, some manufacturers have developed industrial servo valves specifically for industrial applications. For example, in 1963, Moog Company introduced the first 73 series servo valve products specially used in industrial occasions. Subsequently, more and more servo valves developed specifically for industrial use appeared. They have the following characteristics: large volume, easy to manufacture; The valve body is made of aluminum (steel can also be used if necessary); The independent first stage is easy to adjust and maintain; Mainly used in low-pressure occasions below 14MPa; Try to form serialized and standardized products. However, the branch of Moog in Germany mainly focuses on the application of servo valves in high-pressure situations. Generally, the working pressure is 2 1 MPa, and some even reach 35MPa, which makes the design of valves focus on the reliability under high pressure. With the wide application of servo valves in industrial occasions, companies have introduced proportional valves suitable for industrial occasions. Its characteristic is low cost. Although the control accuracy is not as good as that of servo valve, its shortcomings are made up by advanced control technology and advanced electronic devices, making its performance and efficacy close to that of servo valve. 1973, Moog company converted some servo valves into standard interfaces of proportional valves for industrial applications. Bosch has developed its iconic ejector pilot stage and flat servo valve with live feedback. 1974, Moog company introduced a three-stage electric feedback servo valve with low cost and large flow. Vickers Company has developed a KG proportional valve with pressure compensation. Rexroth, Bosch and other companies have developed proportional valves with two coils to control the bidirectional movement of the valve core, and so on.