Butterfly valve sealing pair has metal to metal hard seal, also have metal to rubber or plastic soft seal. The sealing ring can be placed on the butterfly plate or on the valve body. This paper divides the sealing butterfly valve structure in detail.
According to the placement position of the butterfly plate in the valve, the butterfly valve can be made into a symmetrical center (type I), called the import center line butterfly valve, offset (type H) (single eccentric, double eccentric and three eccentric, respectively called the import single eccentric butterfly valve, double eccentric butterfly valve, three eccentric butterfly valve) or variable eccentric butterfly valve.
Butterfly valve sealing structure form: single eccentric seal, double eccentric seal, three eccentric seal, variable eccentric seal, various types of structure butterfly valve sealing principle is described as follows:
(1) Centrelined butterfly valve
The center line butterfly valve, the stem axis line and the butterfly plate center plane in the same plane and the valve body pipe center line vertical intersection, and the butterfly plate on both sides of the area for the stem axis symmetry. The middle line butterfly valve is generally made of the form of rubber lining, because of the simple structure, the center symmetry (type I) two-way sealing effect is the same, and the flow resistance is small, the switching torque is small, so it is widely used in the medium and small butterfly valve. But because the shaft head is often in a state of friction, wear faster than other parts, easy to leak here, so the rubber lining butterfly valve sometimes in the shaft head lined with PTFE film to reduce friction or increase the spring to compensate for wear. Obviously, the middle line such as metal to metal, to seal some difficulties, oblique plate and bias plate butterfly valve shaft head without friction, but their flow resistance and sealing torque are greater than the center symmetric butterfly plate. VTON water for the conventional butterfly valve, generally adopt the middle line structure.
2, single eccentric seal butterfly valve sealing principle
Because on the basis of single eccentric butterfly valve, the rotary center of the butterfly plate (both valve shaft center) and the center line of the body form size offset, make the butterfly valve in the process of opening, the butterfly plate sealing surface will be more quickly than single eccentric sealing butterfly valve from the valve seat sealing surface, butterfly plate rotation to 8 ° ~ 12 °, the butterfly plate seal face completely from the valve seat seal, when fully open, A larger gap is formed between the two sealing faces. The design of the butterfly valve greatly reduces the mechanical wear and crowding deformation between the two sealing faces, so that the sealing performance of the butterfly valve is improved.
3, double eccentric seal butterfly valve sealing principle
Due to a β Angle bias between the center line of the valve seat and the center line of the valve body on the basis of the double eccentric butterfly valve, the sealing surface of the butterfly plate is immediately detached from the sealing surface of the valve seat at the opening moment of the butterfly valve in the process of valve opening, and it will contact and compress the sealing surface of the valve seat at the closing moment. When fully opened, a gap is formed between the two sealing faces and the double eccentric seal butterfly valve. The design of the butterfly valve completely eliminates the mechanical wear and abrasion between the two sealing faces, so that the sealing performance and service life of the butterfly valve have been greatly improved. VTON hard seal butterfly valve and clamp hard seal butterfly valve, welding butterfly valve, generally used is double eccentric structure.
4, three eccentric butterfly valve
The three eccentric butterfly valve rotates the positive cone Angle by an Angle to the oblique cone Angle, so that the eccentricity E can be reduced, and the opening torque will also be reduced. Of course, this is just an intuitive understanding of where the actual axis should be set or three-dimensional motion analysis should be used to determine whether the sealing pair will interfere. Worth pointing out that not only is the triple eccentric butterfly valve sealing ring can be designed into multi-layer type, also can make U like Neles or o-ring, sometimes even can use the non-metallic materials such as rubber, ptfe, but using non-metallic elastic sealing material, is it necessary to make it triple eccentric questionable (double eccentric).
5, variable eccentric seal butterfly valve sealing principle
The unique feature of the variable eccentric butterfly valve is that the valve stem shaft of the butterfly plate is a three-section shaft structure. The three-section shaft shaft of the valve stem is concentric, and the center line of the center axis and the two ends of the axis deviate from a center distance, and the butterfly plate is installed on the middle shaft. This eccentric structure makes the butterfly plate become double eccentric in the fully open position and single eccentric when the butterfly plate turns to the closed position. Due to the action of the eccentric shaft, when close to closing, the butterfly plate moves into a distance to the sealing cone of the valve seat, and the butterfly plate and the sealing surface of the valve seat are consistent to achieve reliable sealing performance.
Because the rotary center of the disc (i.e., the valve shaft center) and disc sealing section according to the eccentric set, make the butterfly valve in the process of opening, the butterfly plate sealing surface gradually from the valve seat sealing surface, butterfly plate rotation to 20 ° ~ 25 °, the butterfly plate seal face completely from the valve seat sealing surface, fully open, the formation of space between the two sealing surface, making the butterfly valve in the process of opening and closing, The relative mechanical wear and extrusion between the two sealing faces are greatly reduced, thus ensuring the seal of the butterfly valve.
