Ventilation butterfly valve welded steel plate manufacturing, with a short structural size, light weight, easy installation and so on. The valve driving torque is small, open and close flexible, easy to operate. The sealing ring set on the valve body sealing oil, no visible gap between side, the leakage rate is small. The butterfly plate and the body of the expansion gap, can effectively prevent thermal expansion and contraction caused by the blocking phenomenon. The valve can be equipped with a variety of driving devices, such as manual devices, worm gear transmission, pneumatic devices, electric devices. The ventilation valve is widely used in metallurgy, chemical, electric power, building materials, division of mines and other industrial pipelines, gas control or regulation medium.