Butterfly valve single. Double. Triple eccentric butterfly valve difference
The structural features of the butterfly valve are stem axis, disc center and body center in the same position.Simple structure and convenient manufacture.Common rubber lined butterfly valves belong to this category.The disadvantage is that the butterfly plate and the seat are always in the state of extrusion, scraping, resistance distance is large, wear fast.In order to overcome extrusion, scratch, to ensure the sealing performance, the valve seat is basically made of rubber or polytetrafluoroethylene and other elastic materials, but also therefore in use by the temperature limit, this is why traditionally people think butterfly valve is not high temperature resistant reason.
2.Single eccentric butterfly valve
In order to solve the extrusion problem between butterfly plate and seat of concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the stem axis deviates from the center of butterfly plate, so that the upper and lower ends of butterfly plate are no longer rotary axis, and the excessive extrusion between the upper and lower ends of butterfly plate and seat is reduced.But because the single eccentric structure in the valve in the entire switching process of the butterfly plate and the seat of the scraping phenomenon does not disappear, in the application range and concentric butterfly valve is similar, so the use of little
On the basis of the single eccentric butterfly valve is further improved shape is currently the most widely used double eccentric butterfly valve.The structure is characterized by that the valve stem axis deviates from both the disc center and the body center.The double eccentric effect enables the butterfly plate to detach from the seat immediately after the valve is opened, greatly eliminating unnecessary excessive squeezing and scraping between the butterfly plate and the seat, reducing the opening resistance distance, reducing wear and increasing the life of the seat.The greatly reduced scraping also enables double eccentric butterfly valves to use metal seats, improving the application of butterfly valves in the high temperature field.But because its sealing principle belongs to the position sealing structure, namely butterfly plate and seat sealing surface for line contact, through butterfly plate extrusion seat caused by elastic deformation to produce sealing effect, so the close position requirements are very high, low pressure capacity, this is why traditionally people think butterfly valve is not resistant to high pressure, the leakage of large reason.
To withstand high temperature, must use a hard seal, but the leakage of large;To have zero leakage, a soft seal must be used, but cannot withstand 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.