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.

近年來，超低溫閥門的用途越來越廣，是石油化工、空氣分離等工業不可缺少的重要設備之一，其工作介質不僅溫度低，而且大部分或有毒性，又或易燃易爆，因此決定了對閥門用材及設計等諸多特殊要求。不僅要求在設定的溫度下能正常工作，同時也要保證在常溫下的工作性能。

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.

低溫閥閥門與常溫閥門相比，低溫閥門填料部位都是加高的，并且采用加長閥桿。其目的是減少外界傳入裝置中的熱量；保證填料箱部位的溫度在0℃以上，使填料可以正常工作；防止因填料函部分過冷而使處在填料函部位的閥桿以及閥蓋上部的零件結霜或凍結。

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.

長頸閥蓋的設計主要是頸部長度L的設計，L指的是填料函底部到上密封座上表面的距離，它和材料的導熱系數、導熱面積及表面散熱系數、散熱面積等因素有關，計算比較繁瑣，一般由實驗法求得。 溫度高于-100℃時可選用鐵素體不銹鋼，溫度低于-100℃時選用奧氏體不銹鋼，低壓和小口徑閥門可選用銅合金或鋁合金，閥體應能充分承受溫度變化而引起的膨脹、收縮，且閥座部分的結構不會因溫度變化而產生變形。

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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