1.Concentric butterfly vlave.
The Concentric butterfly valve have this feature : central line of valve stem shaft, disc center, body center is in the same position. For easy construct, it's convenient to produce. The generally rubber lined butterfly valve belong to this category. But the disadvantage is the disc and valve seat is always in the squeeze, scratch status, resistance, wear fast. In order to overcome the squeeze, scratch, and ensure the sealing performance, the seat is basically made of rubber or PTFE and other flexible materials, this is why the kind of butterfly valve can not be used for high temperature.
2.Triple offset butterfly valve.
Triple offset is also named three eccentric butterfly valve. The first eccentric is the center of stem rotates off from the centerline of seat to ensure tight seat between the seat and the disc. The second eccentric is stem rotation center and seat center deviation, when the valve open, it makes the disc rapidly separated fro the sealing surface. The third eccentric is the center of the cone of the sealing ring deviates from the central line of valve, thus completely eliminating the friction between the disc and the valve seat.
Comparing concentric butterfly valve, the triple offset butterfly valve have the advantage that , valve can be used in high temperature which more than 200 degree C; the valve can be used for partical service; the valve is also zero-leakage. Because of these advantages, triple offset have better performance than concentric butterfly valve.
Zhejiang Zhengfeng Valve