The cast iron butterfly valve, also known as the flap valve, is a simple regulating valve and can also be used for switching control of low pressure pipeline media.A butterfly valve is a type of valve in which the closing member (valve or disc) is a disc that rotates around the valve shaft to open and close, and is mainly used for cutting and throttling on the pipeline. The butterfly valve opening and closing member is a disc-shaped butterfly plate that rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjusting. The butterfly valve is normally less than 90° from full opening to full closing. The butterfly valve and the butterfly rod have no self-locking capability. For the positioning of the butterfly plate, a worm gear reducer is added to the valve stem. The use of a worm gear reducer not only enables the disc to have a self-locking capability, but also stops the disc at any position and improves the valve's operating performance.The characteristics of the industrial special butterfly valve can withstand high temperature, the applicable pressure range is also high, the valve has a large nominal diameter, the valve body is made of carbon steel, and the sealing ring of the valve plate uses a metal ring instead of the rubber ring. Large high temperature butterfly valves are manufactured by steel plate welding and are mainly used for flue ducts and gas pipes of high temperature media.