Ultra-low temperature ball valves are mainly used in the installations of liquefied natural gas, liquefied petroleum gas and air separation industries. The output liquid cryogenic medium includes: liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc. These media are not only flammable and explosive, but also gasification occurs when they are heated or flashed, and their volume expands sharply during gasification. If the valve conveying these fluids has a closed valve cavity and the structural design is unreasonable, it will cause the valve cavity to exceed Pressure, resulting in media leakage, and even valve cracking, causing accidents.