Butterfly valve development history
First, the concentric butterfly valve is characterized by having the stem axis, the butterfly center, and the body center all aligned in the same position. This design offers a simple structure, making it easy to manufacture. Common examples include rubber-lined butterfly valves. However, one major drawback is that the disc and the seat are constantly under squeezing and scraping, leading to high resistance and rapid wear. To reduce this issue and ensure good sealing performance, the seat is typically made of elastic materials like rubber or PTFE. But these materials have temperature limitations, which is why traditional concentric butterfly valves are not suitable for high-temperature applications.
Next, the single eccentric butterfly valve was developed to address the squeezing problem between the disc and the seat. In this design, the stem axis is offset from the center of the butterfly plate, so the disc no longer rotates around the same axis as the seat. This helps reduce the over-squeezing and scraping during operation. However, even with this improvement, the disc and seat still experience some scraping throughout the entire opening and closing process. As a result, its application range is similar to that of the concentric type, and it is used less frequently.
Then comes the double eccentric butterfly valve, which is an advanced version of the single eccentric design. It features two offsets: the stem axis is not only off-center relative to the butterfly plate but also to the body center. This dual eccentricity allows the disc to quickly separate from the seat when the valve is opened, significantly reducing unnecessary squeezing and scraping. As a result, the opening resistance is lower, wear is minimized, and the seat life is extended. This design also enables the use of metal seats, making the valve suitable for high-temperature environments. However, because the sealing mechanism relies on line contact between the disc and the seat, the sealing effect depends on the elastic deformation of the seat. This leads to strict requirements for the closing position, limited pressure capacity, and higher leakage, which is why traditional butterfly valves are often seen as having poor sealing performance.
Finally, the three eccentric butterfly valve was developed to solve the conflict between high-temperature resistance and zero leakage. While hard seals allow for high-temperature use, they often result in significant leakage, and soft seals provide tight sealing but cannot withstand high temperatures. The three eccentric design introduces a third offset, where the conical axis of the sealing surface is shifted relative to the body’s cylindrical axis. This results in an asymmetric sealing surface, which is oval-shaped rather than rectangular. The seal is achieved through torque rather than elastic deformation, meaning the valve relies entirely on contact pressure for sealing. This approach eliminates the need for elastic deformation, enabling true zero leakage with metal seats while also handling high pressures and temperatures effectively. Overall, the three eccentric butterfly valve represents a significant advancement in sealing technology and is widely used in demanding industrial applications.
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