The concentric butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve, and triple eccentric butterfly valve reflect a process of increasingly labor-saving opening and closing, and less and less wear on the sealing surface. By setting the position of the butterfly valve plate shaft, the sealing and opening status of the butterfly valve can be changed.

Concentric Butterfly Valves
The structural feature of a concentric butterfly valve is that the valve stem axis, butterfly plate center, and valve body center are in the same position. Generally speaking, if a concentric butterfly valve can be used, try to use it as much as possible. Because the sealing requirements of the concentric butterfly valve are not high in terms of structure or operation, it belongs to conventional products. To overcome squeezing, scraping, and ensure sealing performance, the valve seat of the concentric butterfly valve is made of elastic materials such as rubber or polytetrafluoroethylene, which is a soft sealing butterfly valve. This places temperature limitations on the use of the concentric butterfly valve. In order to solve the squeezing between the butterfly plate and valve seat of the concentric butterfly valve, a single eccentric butterfly valve has also been produced. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate.

Double Eccentric Butterfly Valves
Double eccentric butterfly valves are the most widely used. Their structural feature is that the axis of the valve stem deviates from both the center of the butterfly plate and the valve body. It deviates from two central positions, so it is called a double eccentric butterfly valve. Many double eccentric butterfly valves are line sealed, causing friction between the butterfly plate and the valve seat when the sealing surface is closed, resulting in excellent sealing effect. It has the characteristics of small area and high pressure. After the valve is opened, the butterfly plate can quickly detach from the valve seat, greatly eliminating unnecessary excessive compression and scraping between the butterfly plate and the valve seat, reducing the opening resistance distance and wear, and improving the service life of the valve seat.

Triple Eccentric Butterfly Valves
The triple eccentric butterfly valve has undergone a third eccentricity on the basis of the double eccentric butterfly valve, and the shape of the sealing pair is not a straight cone, but an inclined cone. The stem shaft of a three eccentric butterfly valve is a three section shaft structure. The two shaft segments of this three section shaft stem are concentric, and the axis centerline of the center segment deviates by one center distance from the axes of both ends. The butterfly plate is installed on the intermediate shaft section. This eccentric structure makes the butterfly plate double eccentric when in the fully open position, and single eccentric when it rotates to the closed position. Because of the action of the eccentric shaft, when approaching closure, the butterfly plate moves a distance into the sealing cone of the valve seat, and the butterfly plate matches the sealing surface of the valve seat, achieving reliable sealing performance. It compensates for the contradiction between the poor sealing performance of hard seals and the good sealing effect of soft seals, but they are not resistant to high temperatures.