In the past few years, due to the imperfect manufacturing technology of valves in China, the application of butterfly valves in early production has been greatly limited because they can not withstand high temperature and pressure and have large leakage. In order to meet the requirements of various working conditions, butterfly valves have evolved from concentric butterfly valves to single eccentric butterfly valves, Triple Eccentric Butterfly Valve and Double Eccentric Butterfly Valve. The structure of concentric butterfly valve is characterized by the same position of stem axis, butterfly plate center and body center. It is simple in structure and easy to manufacture. The disadvantage is that the butterfly plate and valve seat are always in the state of extrusion and scratch, with large resistance distance and fast wear and tear. In order to solve the extrusion problem of butterfly plate and seat of concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the axis of the stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotation axis, and the excessive extrusion of the lower and lower ends of the butterfly plate and the seat is dispersed and alleviated. However, due to the single eccentricity structure in the whole process of valve switching only to a certain extent, but did not eliminate the phenomenon of butterfly plate and seat scratch, in the application scope and concentric butterfly valve are much the same, so the use is not much.

On the basis of single eccentric butterfly valve, the double eccentric butterfly valve which is widely used at present is further improved. Its structural characteristics are that the axis of the stem deviates from the center of the butterfly plate and the center of the valve body.

The effect of double eccentricity enables the butterfly plate to detach from the seat immediately after the valve is opened, greatly eliminating unnecessary over-extrusion and scratch between the butterfly plate and the seat, reducing the opening resistance, reducing wear and prolonging the service life of the valve seat. The scratch is greatly reduced. At the same time, metal seats can be used for double eccentric butterfly valves, which improves the application of butterfly valves in high temperature field. But because its sealing principle is position sealing structure, that is, the sealing surface of butterfly plate and seat is in line contact, and the elastic deformation caused by butterfly plate extruding the seat produces sealing effect, it requires high closing position (especially metal seat) and low pressure bearing capacity, which is the reason why butterfly valve is traditionally considered not to withstand high pressure and large leakage.
To withstand high temperature, hard seals must be used, but the leakage is large; to zero leakage, soft seals must be used, but not high temperature. In order to overcome the contradiction of double eccentricity butterfly valve, the third eccentricity of butterfly valve was carried out.
Triple Eccentric Butterfly Valve is characterized by elliptic cone shape of the valve plate. The conical axis of the sealing surface of the butterfly plate is oblique to the cylinder axis of the body while the axis position of the double eccentric stem is eccentric. That is to say, the sealing section of the tri-eccentric butterfly plate is no longer circular, but ellipse. The shape of the sealing surface is asymmetric, one side inclines to the body center line, the other side is parallel to the body center line. The greatest characteristic of three eccentricity is that it fundamentally changes the sealing structure, not the position seal, but the torsional seal, that is, it does not rely on the elastic deformation of the seat, but completely relies on the contact surface pressure of the seat to achieve the sealing effect.
Triple Eccentric Butterfly Valve have evolved successively through Single-eccentric and double-eccentric butterfly valves, and their performances have been continuously optimized and improved to form a Triple Eccentric Butterfly Valve with good performances in the current market.