As the name suggests, low-temperature valves are valves that can work in cryogenic low-temperature conditions. The demarcation of their working temperature usually refers to valves with working temperature lower than - 40 ℃ as low-temperature valves. They are mainly used in gas liquefaction, separation, transportation and storage equipment. The operating temperature can reach below - 270 ℃. At present, there are gate valves, globe valves, check valves, ball valves Butterfly valve and throttle valve.

近年来，超低温阀门的用途越来越广，是石油化工、空气分离等工业不可缺少的重要设备之一，其工作介质不仅温度低，而且大部分或有毒性，又或易燃易爆，因此决定了对阀门用材及设计等诸多特殊要求。不仅要求在设定的温度下能正常工作，同时也要保证在常温下的工作性能。

In recent years, ultra-low temperature valves are used more and more widely. They are one of the indispensable and important equipment in petrochemical industry, air separation and other industries. Their working medium is not only low temperature, but also most of them are toxic, flammable and explosive. Therefore, many special requirements for valve materials and design are determined. It is required not only to work normally at the set temperature, but also to ensure the working performance at room temperature.

低温阀阀门与常温阀门相比，低温阀门填料部位都是加高的，并且采用加长阀杆。其目的是减少外界传入装置中的热量；保证填料箱部位的温度在0℃以上，使填料可以正常工作；防止因填料函部分过冷而使处在填料函部位的阀杆以及阀盖上部的零件结霜或冻结。

Compared with normal temperature valves, the packing parts of low temperature valves are raised, and the extended valve stem is adopted. The purpose is to reduce the heat from the outside into the device; Ensure that the temperature of the stuffing box is above 0 ℃, so that the stuffing can work normally; Prevent the valve stem at the stuffing box and the parts on the upper part of the bonnet from frosting or freezing due to the undercooling of the stuffing box.

长颈阀盖的设计主要是颈部长度L的设计，L指的是填料函底部到上密封座上表面的距离，它和材料的导热系数、导热面积及表面散热系数、散热面积等因素有关，计算比较繁琐，一般由实验法求得。 温度高于-100℃时可选用铁素体不锈钢，温度低于-100℃时选用奥氏体不锈钢，低压和小口径阀门可选用铜合金或铝合金，阀体应能充分承受温度变化而引起的膨胀、收缩，且阀座部分的结构不会因温度变化而产生变形。

The design of the long neck bonnet is mainly the design of the neck length L, which refers to the distance from the bottom of the stuffing box to the upper surface of the upper sealing seat. It 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 cumbersome, which is generally obtained by the experimental method. Ferritic stainless steel can be selected when the temperature is higher than - 100 ℃, austenitic stainless steel can be selected when the temperature is lower than - 100 ℃, copper alloy or aluminum alloy can be selected for low-pressure and small-diameter valves, the valve body shall be able to fully withstand the expansion and contraction caused by temperature change, and the structure of the valve seat will not be deformed due to temperature change.

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