The basic principle of electric plug valve is based on the plug sealed in the conical plug body. The valve can not be opened or closed without this plug. The plug is screwed into the valve seat to open or close the valve, thus causing friction between the plug and the middle valve seat. The operating torque is affected by the magnitude of this friction. The pressure on the fluid does not affect the operating torque, but it plays a vital role in the torque of other operating processes. 　　

With the rapid development of industrial technology, more stringent requirements have been put forward for the valve industry, especially for the use of butterfly valves in cryogenic media. In addition to meeting the performance of general valves at room temperature, more importantly, the reliability of valve sealing, flexibility of action and other special requirements for cryogenic valves at low temperature. Because butterfly valves have a series of advantages, such as compact structure, small volume, light weight (40%~50% less fluid resistance than gate valves with the same pressure and diameter), quick opening and closing, they are widely used. However, more than 80% of the valves used in some cryogenic devices in China, such as natural combustion liquefaction equipment, air separation equipment, pressure swing adsorption equipment and other chemical industries, are still stop valves or gate valves, and the number of butterfly valves is very small. The main reason is that the sealing performance of the metal seal butterfly valve of the plug valve is poor under the low temperature condition, as well as the internal and external leakage of the medium caused by other reasons such as unreasonable structure, which seriously affects the safety and normal operation of these low-temperature equipment and cannot meet the requirements of low-temperature equipment.