Butterfly valve single, double, three eccentric butterfly valve
The structural characteristics of the central butterfly valve are that the stem axis, the disc center and the body center are in the same position.Simple structure and convenient manufacture.Common rubber - lined butterfly valve belongs to this category.Disadvantages are due to disc and seat always in the squeezing, scraping state, large resistance distance, wear fast.In order to overcome the squeeze, scratch, to ensure the sealing performance, the seat is basically rubber or ptfe and other elastic materials, but also in the use of temperature restrictions, which is why traditionally people do not think the butterfly valve high temperature.
In order to solve the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve, the single-eccentric butterfly valve is produced. Its structural feature is that the valve stem axis deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotary axis, and the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat is reduced.But because of the single eccentric structure in the valve in the whole switching process of the butterfly and seat scraping phenomenon did not disappear, in the application range and concentric butterfly valve with little difference, so the use of less.
Double eccentric butterfly valve
Based on the single eccentric butterfly valve further improved molding is currently the most widely used double eccentric butterfly valve.Its structure characteristic is in the valve stem axis both deviates from the butterfly plate center, also deviates from the body center.The effect of double eccentricity makes the butterfly plate can be removed from the seat immediately after the valve is opened, greatly eliminating the butterfly plate and seat unnecessary excessive extrusion, scraping phenomenon, reduce the opening resistance, reduce the wear, increase the life of the seat.
The significant reduction of the scratch, but also makes the double eccentric butterfly valve can also use metal seats, improve the butterfly valve in the high temperature field of application.But because its sealing principle is the position sealing structure, that is, the sealing surface of the butterfly plate and the seat is line contact, through the butterfly plate squeezing the seat caused by the elastic deformation of the sealing effect, so the requirements for the close position is high, the ability to bear pressure is low, which is why traditionally people think that the butterfly valve is not resistant to high pressure, leakage is large.
Eccentric butterfly valve
To withstand high temperature, must use a hard seal, but large leakage;To zero leakage, must use a soft seal, but not resistant to high temperature.In order to overcome the contradiction of double eccentric butterfly valve, the third eccentric butterfly valve was carried out.The structure characteristics of the double eccentric eccentric axis of the stem position at the same time, make the butterfly plate type sealing face of the cone axis deflection in the cylindrical axis of ontology, that is to say, after the third eccentric, butterfly plate sealing section is no longer true circle, but the ellipse, and so the seal face shape asymmetry, tilt to the center line of the ontology, on the other side is parallel to the centerline of ontology.
This the third time that the biggest characteristic of eccentric fundamentally changed the seal structure and seal position is no longer, but the torque seal, namely not rely on the elastic deformation of the seat, but completely rely on the seat of the contact pressure to achieve sealing effect, thus solved the problem of metal seated zero leakage at a stroke, and because of the contact pressure and interface stress is proportional to the, resistance to high pressure high temperature is solved.