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One, the center line butterfly valve (concentric butterfly valves)
Structure characteristics of the center line butterfly valve as the axis of the stem and disc center, ontology in the same position.
Simple structure, convenient manufacturing.
Common line with rubber butterfly valve which belongs to and so on.
Defect is due to the butterfly plate and valve seat remain the state of extrusion, scratches, is apart from the big, fast wear.
To overcome the extrusion, scratches, ensure the sealing performance, basically use the elastic material such as rubber or ptfe seat, but also because of the sealing material in use is limited by temperature, which is why people traditionally butterfly valve is not the cause of the high temperature resistant. 
Second, the single eccentric butterfly valve
Structure characteristics of single eccentric butterfly valve as the axis of the stem off the butterfly plate center, so that the butterfly plate up and down side is no longer a rotary axis, scattered, reduced the butterfly plate and end and the seat of the excessive extrusion, solved the concentric butterfly butterfly plate and the seat of the extrusion problems.
But as a result of single eccentric structure adjustment in the process of the switch valve plate and valve seat scratches phenomenon did not disappear, on the application scope and concentric butterfly valves are the same, is not much. 
Three, double eccentric butterfly valve
Double eccentric butterfly valve in single eccentric butterfly valve on the basis of further improvement, which is the most widely used.
Its structure characteristics is in the center of the axis of the stem is deviating from the butterfly plate, also deviates from the center of ontology.
The effect of the double eccentric butterfly plate can immediately after the valves are open from the seat, greatly eliminates the butterfly plate and valve seat of unnecessary phenomenon of excessive extrusion, scratches, reduce the opening distance, reduces the abrasion resistance, improve the seat life.
Scraping slash, but also makes the double eccentric butterfly valve can also use a metal seat, improves the application in the field of high temperature.
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.
Four, three eccentric butterfly valve
To high temperature resistant, hard seal must be used, but the large amount of leakage;To zero leakage, must use the soft seal, but it is not resistant to high temperature.In order to overcome this contradiction, double eccentric butterfly valve and eccentric butterfly valve for the third time.
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.
The biggest characteristic of the third eccentric is 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 the medium is proportional to the pressure, resistance to high pressure high temperature is solved.