Butterfly valve single, double, triple eccentric butterfly valve difference

First, the center butterfly valve

    The structural characteristics of the butterfly valve are the stem center, disc center and body center at the same position. The structure is simple and easy to manufacture. The common lining butterfly valve belongs to this category. The disadvantage is that the butterfly plate and the valve seat are always in the state of squeezing, scraping, large drag, and fast wear. In order to overcome the squeezing, scratching, and guaranteeing the sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but is also subject to temperature restrictions in use, which is why it is conventionally considered that the butterfly valve is not resistant to high temperatures. the reason.

Two, single eccentric butterfly valve

 

    In order to solve the problem of the extrusion of the butterfly plate and the valve seat of the concentric butterfly valve [ http:// ], a single eccentric butterfly valve has been produced. Its structural feature is that the stem axis deviates from the center of the butterfly plate so that the butterfly plate is not It becomes the axis of rotation, dispersion, and reduces the excessive extrusion of the lower end of the butterfly plate and the valve seat. However, due to the single eccentric structure, the scraping phenomenon of the butterfly plate and the valve seat has not disappeared during the entire switching process of the valve, and the application scope and the concentric butterfly valve are similar, so it is not used much.

Three, double eccentric butterfly valve

The most widely used double-eccentric butterfly valve is currently further improved on the basis of single-offset butterfly valves. Its structural feature is that the stem axis is both offset from the center of the disc and away from the center of the body. The effect of double eccentricity makes the butterfly plate quickly disengage from the valve seat after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scraping of the butterfly plate and the valve seat, reduces the open distance, reduces wear, and improves Seat life. The drastic reduction of the scratches also allows the use of metal seats for double-offset butterfly valves, which increases the application of butterfly valves in high temperature applications. However, because its sealing principle is a position seal structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, and the sealing effect is caused by the elastic deformation caused by the disc pressing the valve seat, so the requirement for the closed position is very high (especially the metal Seat), low pressure capability, which is why traditionally people think that the butterfly valve is not resistant to high pressure and large leakage.

 

Four and three eccentric butterfly valves

 

    To be resistant to high temperatures, hard seals must be used, but leakage is large; for zero leakage, soft seals must be used but not high temperatures. In order to overcome the contradiction of the double eccentric butterfly valve, the third eccentricity of the butterfly valve was performed. The structural feature is that the double-eccentric valve stem axis position is eccentric and the cone-shaped axis of the butterfly plate sealing surface is skewed to the body cylinder axis. That is, after the third eccentricity, the sealing profile of the butterfly plate is not In addition, the shape of the sealing surface of the circle is oval, and the shape of the sealing surface is therefore asymmetrical. One side is inclined to the centerline of the body, and the other side is parallel to the centerline of the body.

    The biggest feature of this third eccentricity is that it fundamentally changes the seal structure, no longer the position seal, but the torque seal, that is, not relying on the elastic deformation of the valve seat, but completely rely on the contact surface pressure of the valve seat to achieve sealing The effect, therefore, solves the problem of zero leakage of the metal valve seat in one stroke, and the pressure and pressure of the contact surface are proportional to the pressure, and the high pressure and high temperature are also solved .