A butterfly valve is a valve which can be used for isolating or regulating flow. 

The closing mechanism takes the form of a disk. Operation is similar to that of 

a ball valve, which allows for quick shut off. Butterfly valves are generally favored 

because they are lower in cost to other valve designs as well as being lighter in 

weight, meaning less support is required. The disc is positioned in the center of 

the pipe; passing through the disc is a rod connected to an actuator on the 

outside of the valve. Rotating the actuator turns the disc either parallel or 

perpendicular to the flow. Unlike a ball valve, the disc is always present within 

the flow, so a pressure drop is always induced in the flow, regardless of valve 

position.

Types

1. Concentric butterfly valves - this type of valve has a resilient rubber 

   seat with a metal disc.

2. Doubly-eccentric butterfly valves (high-performance butterfly valves or 

   double-offset butterfly valves) - different type of materials is used for 

   seat and disc.

3. Triply-eccentric butterfly valves (triple-offset butterfly valves) - the 

   seats are either laminated or solid metal seat design.