2. Classification according to sealing surface material
(1) Soft seal butterfly valve 1) The sealing pair is composed of non-metallic soft materials and non-metallic soft materials. 2) The sealing pair is composed of metal hard materials and non-metallic soft materials.
(2) Metal hard seal butterfly valve. The sealing pair is composed of hard metal material to hard metal material.

Basically, gate valve and globe valve can be selected if the temperature of valve suitable for steam pipeline is less than 425 ℃. Select alloy valve above 400 ℃. The gate valve is mainly used for the main steam valve of the steam pipeline, that is, the valve that is not normally opened and closed. The stop valve is mainly used for the valve close to the equipment by the user, because this valve has a good regulating effect on the flow. The selection of valves for steam pipeline mainly depends on temperature, pressure, function and installation position.