Reasons for using long-neck valve covers in low-temperature valves

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Reasons for using long-neck valve covers in low-temperature valves (purely personal opinion). Additional information from fellow sailors: Valves that can handle medium temperatures ranging from -40°C to -196°C are referred to as low-temperature valves, and such valves generally use long-neck valve covers. Low-temperature valves include low-temperature emergency shut-off valves, low-temperature globe valves, low-temperature check valves, as well as valves designed specifically for LNG and NG; they are mainly used in chemical plants that produce 300,000 tons of ethylene or liquefied natural gas. The liquid cryogenic media produced, such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, and liquefied petroleum products, are not only flammable and explosive but also vaporize when heated; during this vaporization process, their volume expands by hundreds of times. The use of a long-neck valve cover is specified because: (1) it provides protection for the packing box of low-temperature valves, as the sealing performance of the packing box is one of the key factors in low-temperature valves. If there is a leak at this stuffing box, it will reduce the insulation effect, causing the liquefied gas to vaporize. At low temperatures, as the temperature drops, the elasticity of the packing gradually disappears, resulting in a decline in its sealing performance. The leakage of fluid causes freezing at the junction between the packing and the valve stem, which hinders the proper operation of the valve stem. Additionally, the up and down movement of the valve stem can scratch the packing, leading to severe leaks. Therefore, it is necessary to ensure that the temperature at the filler nozzle area remains above 8°C. (2) The long-neck valve cover structure facilitates the wrapping of insulation material to prevent heat loss from the valves at low temperatures. (3) The long-neck structure of the low-temperature valve facilitates the quick replacement of the valve’s main components by removing them through the valve cover. Since the process pipes and valves in the cold section of the equipment are often installed within the ’cold box’, the long-neck valve cover can extend through the wall of the ’cold box’. When replacing the main components of the valve, it is sufficient to carry out the replacement through the valve cover, without the need to disassemble the valve body. The valve body is welded to the pipeline, which minimizes leaks in the cryogenic tank and ensures the seal integrity of the valve.