The valve is the control device of the fluid pipeline. Its basic function is to turn on or off the circulation of the pipeline medium, change the circulation of the medium, change the flow direction of the medium, adjust the pressure and flow of the medium, and protect the normal operation of the equipment of the pipeline. The large-scale application of industrial valves is after Watt invented the steam engine. In the past two or three decades, due to the needs of petroleum, chemical, power station, metallurgy, shipbuilding, nuclear power, aerospace, etc., higher requirements were placed on the valve, prompting people to study And the production of high-parameter valves, operating temperature from ultra-low temperature -269 ° C to high temperature 1200 ° C, even up to 3430 ° C, working pressure from ultra-vacuum 1.33x10-8Mpa (1x10-1 mm Hg) to ultra-high pressure 1460MPa, valve diameter from From 1mm to 600mm, even up to 9750mm, the valve material is developed from cast iron and carbon steel to titanium and titanium alloy, high-strength corrosion-resistant steel, etc. The driving mode of the valve is from manual development to electric, pneumatic, hydraulic, program control, numerical control, Remote control, etc. With the continuous development of modern industry, the demand for valves is increasing. A modern petrochemical plant requires tens of thousands of valves and a large amount of valves. Frequent opening and closing, but often due to manufacturing, use selection, improper maintenance, bubble, take-off, dripping, leakage, resulting in flame, explosion, poisoning, burns, or resulting in poor product quality, energy consumption, equipment corrosion Increased material consumption, environmental pollution, and even accidents such as production stoppages have become commonplace. Therefore, people hope to obtain high-quality valves, and also require the use of valves and maintenance levels. At this time, they are engaged in valve operators, maintenance personnel, and engineers. In addition to careful design, reasonable selection, and correct operation of the valve, it is necessary to timely maintain and repair the valve, so that the valve "bubble, take, drip, leak" and various accidents to a minimum.