1. Concentric butterfly valve. The structure of the butterfly valve is characterized by the spindle of the stem, the center of the butterfly plate and the center of the body in the same position. Simple structure and convenient manufacture. The disadvantage is that the butterfly plate and seat always in the extrusion, scraping state, resistance distance, wear fast. In order to overcome extrusion, scraping, to ensure the sealing performance, the seat is basically made of rubber or PTFE and other elastic materials, but it is also limited by temperature, which is usually considered as the reason why the butterfly valve is not resistant to high temperature.
2. Single eccentric butterfly valve
. In order to solve the problem of extrusion between butterfly plate and seat of concentric butterfly valve, the single eccentric butterfly valve
is produced. Its structure is characterized by the axis of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate are no longer the rotation axis, dispersing and reducing the excessive extrusion of the upper and lower ends of the butterfly plate and the cold night. But because of the single eccentric structure into the whole switching process of the valve on the butterfly plate and the scraping phenomenon of the seat and not disappear, in the application of the garden and the concentric butterfly valve is much the same, so not much.
3. Double eccentric butterfly valve
. In the single eccentric butterfly valve on the basis of further improved molding. It is also the most widely used butterfly valve form. Its structure is characterized by the shaft of the valve stem that deviates from the center of the butterfly plate, also deviates from the center of the body. The effect of double eccentricity makes the butterfly plate can be quickly removed from the seat after the valve is opened, it eliminates the unnecessary excessive extrusion of the butterfly plate and the question seat. Scratch phenomenon, reduce the opening resistance, reduce wear, improve the service life. The SIGNIFICANT REDUCTION in SCRATCHING also enables double eccentric valves to use metal seats, improving butterfly valve applications in high temperature areas. It is also true that the sealing principle is based on the position sealing structure, that is, the butterfly plate is in line contact with the sealing surface of the valve seat, and the sealing effect is produced by the elastic deformation caused by the butterfly plate extrusion of the valve seat: therefore, the closing bit egg is highly required. The low bearing capacity is also the reason why butterfly net can not withstand high pressure and leakage is large.
4. Triple offset butterfly valve. To resist high temperature must use a hard seal, and to zero leakage must use a soft seal. In order to overcome these contradictory two points, three eccentric butterfly valve was developed. That on the premise of double eccentric butterfly valve, butterfly plate type sealing face of the cone axis deflection in ontology garden column axis, that is to say, after the third eccentric butterfly plate sealing section is no longer true circle, but the ellipse, and so its sealing surface switch asymmetry, tilting the center line of the ontology, on the other side is equal to the center line of the ontology. The biggest feature of this third eccentric is to fundamentally change the seal structure, no longer a position seal, but a torque seal. That is, it does not depend on the elastic deformation of the seat, but completely depends on the contact surface pressure of the seat to achieve the sealing effect. Therefore, it solves the problem of zero leakage of metal seat at one stroke. And because the contact surface is proportional to the pressure of the medium, the high pressure resistance problem is also solved. However, in theory, three eccentric butterfly sea can achieve zero leakage. But it also depends on careful design, precision manufacturing.