Eccentric butterfly valve is divided into single eccentric butterfly valve, double offset butterfly valve, Three eccentric butterfly valve and variable eccentric butterfly valve. Opposite of concentric butterfly valve. Butterfly valves whose stem axis deviates from the center of the disc and the center of the body at the same time, and the sealing pair is an oblique cone are called eccentric butterfly valves.
(1) Single offset butterfly valve
In order to solve the extrusion problem between the disc and the valve seat of the concentric butterfly valve, the single offset butterfly valve is produced. Disperse and reduce the excessive extrusion of the upper and lower ends of the butterfly plate and the valve seat.
(2) Double offset butterfly valve
On the basis of the single eccentric butterfly valve, the most widely used double offset butterfly valve is further improved and formed. Its structural feature is that the shaft center of the valve stem deviates from the center of the disc and the center of the body. The effect of double eccentricity enables the disc to break away from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching between the disc and the valve seat, reduces the opening resistance, reduces wear, and prolongs the seat life.
(3) Three eccentric butterfly valve
To withstand high temperature, a hard seal must be used, but the amount of leakage is large; to zero leakage, a soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of the double offset butterfly valve, the butterfly valve was eccentric for the third time. The so-called three eccentric butterfly valve means that the shape of the sealing pair is not a positive cone, but an oblique cone.
(4) Variable eccentric butterfly valve
The unique feature of the variable eccentric butterfly valve is that the stem shaft on which the disc is installed is a three-segment shaft structure. The two shaft segments of the three-segment shaft valve stem are concentric, and the center line of the center shaft is deviated from the axes at both ends by a center distance. , the butterfly plate is installed on the intermediate shaft section. Such an eccentric structure makes the disc become double eccentric when the disc is fully open, and becomes single eccentric when the disc is rotated to the closed position. Due to the action of the eccentric shaft, when it is close to closing, the disc moves a distance into the sealing cone surface of the valve seat, and the disc matches the sealing surface of the valve seat to achieve reliable sealing performance.
The butterfly valve and the upper and lower valve shafts are connected by special-shaped holes and special-shaped shafts. During the opening and closing process of the butterfly plate, the function of pinless connection of the butterfly plate floating up and down, left and right is realized, and the interference area between the butterfly plate and the valve seat is reduced. This greatly reduces torque. The floating structure of the butterfly plate realizes the production process of single eccentricity and the function of variable eccentricity. The inner cavity of the valve body is provided with an anti-disc overrun stopper to ensure that the disc is not in place when closed. The upper and lower valve shaft holes of the eccentric butterfly valve body cavity and the upper and lower valve shaft holes of the butterfly plate are protected by bushings to prevent large particles in the medium from entering the valve shaft holes.
