As the name suggests, a cryogenic valve is a valve that can work in cryogenic low temperature conditions. To demarcate its working temperature, a valve with a working temperature lower than -40 °C is usually called a cryogenic valve, which is mainly used for gas liquefaction, Separation, transportation and storage equipment, the operating temperature can reach below -270 ℃, there are gate valve, globe valve, check valve, ball valve,  butterfly valve and throttle valve and other types.

In recent years, the use of ultra-low temperature valves has become more and more extensive, and it is one of the indispensable and important equipment in petrochemical, air separation, natural gas and other industries. , and the permeability is strong, so it determines many special requirements for valve materials and design. It is not only required to work normally at the set temperature, but also to ensure the working performance at normal temperature.

Compared with the normal temperature valve, the low temperature valve has a higher packing part and an extended valve stem. Its purpose is to reduce the heat introduced from the outside into the device; to ensure that the temperature of the stuffing box is above 0 °C, so that the stuffing can work normally; to prevent the valve stem and the upper part of the valve cover from being in the stuffing box due to the overcooling of the stuffing box. parts are frosted or frozen.

The design of the long-neck bonnet is mainly the design of the neck length L. L refers to the distance from the bottom of the stuffing box to the upper surface of the upper sealing seat, which is related to the thermal conductivity, thermal conductivity area, surface heat dissipation coefficient, heat dissipation area and other factors of the material. , the calculation is more complicated, and it is generally obtained by the experimental method. Ferritic stainless steel can be used when the temperature is higher than -100℃, austenitic stainless steel can be used when the temperature is lower than -100℃, copper alloy or aluminum alloy can be used for low pressure and small-diameter valves, and the valve body should be able to fully withstand temperature changes caused by expansion and contraction, and the structure of the valve seat part will not be deformed due to temperature changes.