The structural feature of the butterfly valve is that the stem axis, butterfly plate center and body center are in the same direction. The structure is simple and easy to make. The common rubber lined butterfly valve belongs to this kind. The defect is that the butterfly plate and valve seat are always in kneading, scraping condition, large resistance distance and fast wear. In order to overcome kneading, scratching and ensure the sealing function, the valve seat is basically made of elastic materials such as rubber or polytetrafluoroethylene.

　　butterfly valve
　　But it is also limited by temperature in operation, which is the reason why butterfly valve is not resistant to high temperature. In order to solve the kneading problem between the butterfly plate and valve seat of concentric butterfly valve, single migraine butterfly valve is produced. Its structural feature is that the axis of valve stem violates the center of butterfly plate, so that the upper and lower ends of butterfly plate no longer become reverse axis, disperse and reduce the pressure of butterfly valve Excessive kneading between the upper and lower ends of the plate and the valve seat.
　　However, due to the scratch phenomenon between the butterfly plate and the valve seat in the whole opening and closing process of the valve, the application range of the single migraine butterfly valve is quite different from that of the concentric butterfly valve, so the selection is not much. The double migraine butterfly valve, which is further improved on the basis of the single migraine butterfly valve, is now widely used. Its structural feature is that the axis of the valve stem violates not only the center of the butterfly plate, but also the center of the body.
　　After the valve is opened, the butterfly plate can quickly break away from the valve seat, which greatly eliminates the unnecessary excessive kneading and scratching between the butterfly plate and the valve seat, reduces the open resistance distance, reduces the wear and improves the service life of the valve seat. The scraping is greatly reduced, at the same time, the metal valve seat can also be selected for the double migraine butterfly valve, which improves the application of the butterfly valve in the field of high temperature.