DD343 worm gear flange multi-level metal hard seal butterfly valve butterfly valve in addition to retaining the original butterfly valve has compact structure, small size, light weight, convenient operation, reliable performance, simple maintenance, but also has the characteristics of anti-aging, anti-irradiation, durable, long life, temperature and high pressure resistance, wide application range and so on. Widely used in thermal pipelines, boiler auxiliary systems, petrochemical and metallurgical industries, used to cut off and adjust various non-corrosive and corrosive media.