The structural feature of the midline butterfly valve is that the stem axis, the center of the disc, and the center of the body are at the same position. The structure is simple and convenient to manufacture. A common rubber-lined butterfly valve belongs to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of being squeezed, scraped, large in resistance and fast in wear. In order to overcome the extrusion, scratching and sealing performance, the valve seat is basically made of elastic materials such as rubber or Teflon, but also because the sealing material is limited in temperature, which is why the butterfly valve is not considered to be intolerant. The reason for the high temperature.