A valve is necessary for supply of water, sewage, pipe gas, liquefied petroleum gas, gasoline, light oil, and also for fueling industrial plants, whether the state of gas is vapor or liquid. The type and structure of valve varies from one application to another, and valves are roughly categorized into three types: globe valve, gate valve, ball valve, and butterfly valve. If classified by operation method, they are divided into self-operation type and actuator-operation type. Moreover, if classified by purpose, they are divided into stop valve, pressure-reducing valve, safety valve, etc. Although there is especially no classification of valve by the type of fluid, it matters what type of material is to be used for what part of the valve: what type of metal should be used for valve body and what type of material should be used for sealing. In this sense, the specification of hydrogen valve is special. In case of valve for compressed hydrogen, its structure and material is specially designed and selected for brittleness of compressed hydrogen, and in case of valve for liquefied hydrogen, its structure and material is so specially designed and selected that it can be used under cryogenic condition..
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