According to the different structures of butterfly valves, we distinguish four types of butterfly valves: concentric butterfly valves, single eccentric butterfly valves, double eccentric butterfly valves and triple eccentric butterfly valves.

Concentric butterfly valves, single eccentric butterfly valves, double eccentric butterfly valves and triple eccentric butterfly valves actually reflect a process of opening and closing with less and less effort and less and less wear on the sealing surface. By setting the position of the rotating shaft of the butterfly valve wedge, the sealing and opening states of the butterfly valve can be changed. Under the same conditions, the torque of the valve is greater than that of each opening. When the valve is opened, the rotation angle required for the valve plate to separate from the seal is smaller than the other.

The structural feature of the concentric butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate and the center of the valve body are at the same position. Generally, if concentric butterfly valves can be used, they should be used as much as possible. Because the concentric butterfly valve does not require high sealing performance in terms of structure or operation, it is a conventional product. To overcome squeezing, scraping, and ensure sealing performance, the valve seat of the concentric butterfly valve is basically made of elastic materials such as rubber or polytetrafluoroethylene, which is a soft sealing butterfly valve. This limits the use of concentric butterfly valves to temperature. In order to solve the squeezing problem 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 are the most widely used. Its structural feature is that the valve stem axis deviates from both the center of the butterfly plate and the center of the valve body, thus 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, reducing wear, and improving the service life of the valve seat.

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. It is mostly short distance force and surface sealing. The stem shaft of a three eccentric butterfly valve is a three section shaft structure. The two shaft sections of this three section shaft stem are concentric, and the center line of the center section shaft deviates by one center distance from the two end axes. 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. Due to 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 effect of hard seals and the good sealing effect of soft seals, but they are not resistant to high temperatures.

When to use concentric butterfly valves, double eccentric butterfly valves, or triple eccentric butterfly valves depends mainly on the operating conditions and budget.