Butterfly valves are commonly used valves in industrial water systems, and have become commonly used valves in pipelines due to their small sizes and high cost-effectiveness. Although butterfly valves have fewer types compared to gate valves, they also have a wide range of applications and are suitable for various working conditions. Butterfly valves have replaced gate valves, globe valves, throttle valves, and ball valves on a large scale, and are one of the rapidly developing valve varieties in recent years.

Performance Principles
The butterfly valve adopts a structure where the valve plate rotates along the centerline, so the valve volume is small. By rotating the handle 90 degrees or driving with a worm gear, the valve can be opened by making the valve plate parallel to the flow direction of the medium. Therefore, butterfly valves have the characteristics of simple structure, small volume, light weight, small installation size, convenient operation, and quick opening and closing. They also have sealing and flow regulation characteristics. However, it is not suitable for use in high-pressure environments due to the high resistance of the valve disc and the significant impact of medium pressure on valve opening and closing.
 
In recent years, with the rapid development of technology, new structural forms of butterfly valves have been developed, and eccentric metal seated butterfly valves are one of them. The seat and sealing surface of the eccentric metal seated butterfly valve are made of metal hard alloys, or the butterfly plate soft and hard materials (non-metallic layers sandwiched with metal layers), making the butterfly valve resistant to high temperature, low temperature, wear, erosion, and have good sealing performance, and long service life, which is widely used.
 
Classifications
Butterfly valves are mainly classified into the centerline type and eccentric type according to their structure, with eccentric type divided into single eccentric, double eccentric, and triple eccentric butterfly valves.
 
The sealing performance and service life of centerline butterfly valves, single eccentric butterfly valves, double eccentric butterfly valves, and triple eccentric butterfly valves have been successively enhanced, but the structural difficulty and cost have also increased. Therefore, unless there are special operating conditions, it is often better to choose a more economical and suitable butterfly valve.