Butterfly Valve
Butterfly valves are a form of quarter turn valve, used to control flow in pipes or process lines. They operate using a rotating disc to separate or allow flow, and differ from ball and plug valves due to their use of low torque to operate, but also because of their flat and disc-shaped closure element. Between their relatively simple operation and lower head loss, butterfly valves provide flow control in a wide variety of applications, from slow to fast moving fluids, usually working at a multi-turn angle of 90 degrees or less.
Types of Butterfly Valves
There are two major types of butterfly valves: concentric and eccentric. Concentric butterfly valves feature a disc that is positioned in the center line of the valve body, while eccentric butterfly valves feature a disc that is slightly off center, resting at an angle to create a control damper with less head loss and greater flow control.
Concentric Butterfly Valves
Concentric butterfly valves are the simplest, most economical option. Inside the valve, a disc with a hole in its center moves along the axis of the pipe line. The disc is rotated up to open it fully and allows maximum flow. To cut off all flow, the disc is rotated down until it collides with the valve body. Because of their simple design, most concentric butterfly valves are unidirectional, meaning that the flow of material passes only in one direction. This makes them ideal for applications such as water treatment, water supply and drainage systems.
Eccentric Butterfly Valves
Eccentric butterfly valves differ from concentric valves because the hole in the disc is not in the same center line as the valve body. This design feature causes the disc to move off-center when it is rotated to seal off the flow. The result is a double damper effect, which helps to further reduce the turbulence and noise caused by the flow of material. This allows for greater control of material flow, making it ideal for controlling pressure, media velocity or volume. Eccentric butterfly valves are also bidirectional, meaning that they can be used to cut off the flow of material from either direction. This makes them ideal for applications such as chemical and petroleum products, natural gas and other applications where bidirectional flow is required.
Summary
The major difference between butterfly valves is the design of the disc. Concentric valves have a disc with a hole in its center, while eccentric valves feature a disc that is slightly off center. While both types are used for flow control, eccentric valves are superior in controlling fluid flow, pressure and media velocity. Concentric valves are simpler, more economical and are often unidirectional, while eccentric valves are bidirectional and provide greater control of flow. No matter which valve you choose, butterfly valves are a great choice for controlling and regulating flow in a wide range of applications.
