Butterfly valves are typically used to isolate or regulate the flow of water. There are three main types of butterfly valves: concentric, double eccentric, and triple eccentric. The concentric butterfly valve usually has a rubber seat with a metal disc.
A double eccentric, or high performance butterfly valve, can have a variety of materials for the seat and disc. A triple eccentric butterfly valve, also known as triple offset butterfly valve, can be made with either a laminated or solid metal seat design. The triple offset valve design are used solely in applications that require bi-directional shut-off, such as in oil and gas, chemical factories, and ship building.
The role of a butterfly valve is to regulate the flow in which the disc takes the form of the disk. This process is similar to the process of the ball valve. The disc is positioned in the center of the pipe, and has a rod passing through, which is connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel of perpendicular to the flow. The disc is always present within the flow, which means a pressure drop is then induced in the flow, no matter what the valve position is. This is the major difference from the ball valve.