Triple eccentric butterfly valves' development and use
Development and Application of triple eccentric Butterfly valve? In many Asia-Pacific regions, there is still a strong bias against Butterfly valves due to the limitations of domestic valve design and manufacturing levels and the influence of traditional textbooks. At the same time, Europe and the United States is the advanced developed industry is vigorously promoting the use of butterfly valves.
The reason is simple. Butterfly valves are not what they used to be. The triple eccentric butterfly valve can withstand pressure up to 2500 LBS., temperature as low as -196 ℃, as high as 700℃, seal up to 0 leakage, control ratio up to 100:1 above. That is to say, in a variety of harsh, critical process control pipeline, whether the switch valve or control valve, as long as the proper selection, can now safely use butterfly valves, and low cost.
The excellent performance of butterfly valve is closely related to its eccentricity, evolution and development. In order to meet the requirements of various working conditions, the butterfly valve has experienced the evolution from concentric to single eccentric, double eccentric and triple eccentric. The evolution of butterfly valve and the development and application of triple eccentric butterfly valve are briefly introduced as follows
The structural features of this butterfly valve are stem axis, butterfly plate 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.
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.
Double eccentric butterfly valve in the single eccentric butterfly valve on the basis of further improving the shape is widely used in the current 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 position belongs to the sealing structure, namely the butterfly plate and valve seat sealing surface of line contact, through the butterfly plate extrusion seat sealing effect caused by the elastic deformation, therefore, to the closed position requirement is very high (especially metal seated), low bearing capacity, which is why people traditionally butterfly valve leakage in high pressure resistance, no major reasons.
Triple eccentric butterfly valve to be high temperature resistant, need to use hard seal, but the leakage of large; Zero leakage, need to use a soft seal, but not high temperature resistance. 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.
Characteristic of triple eccentric butterfly valve is fundamentally changed the seal structure and seal position is no longer, but the torque seal, which is not dependent on the elastic deformation of the seat, but 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 the medium is proportional to the pressure, resistance to high pressure high temperature is solved.
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