Butterfly valves are a type of quarter-turn valve used to regulate the flow of a fluid. The valve mechanism requires a 90-degree turn to go from the fully open to the fully closed position. The basic butterfly valve has three primary components: A disc, a stem, and a seat.

The disc is a thin, typically circular, metal plate that opens or closes the valve. When the valve is opened, the disc is aligned parallel to the fluid flow, allowing unrestricted flow. When the valve is shut, the disc is perpendicular to the fluid movement, using its surface area to prevent flow through the pipe.

The stem is a shaft that transmits motion from the handle or actuator to the disc. In some applications, the stem may be combined with the handle or disc as a single component.

The valve seat seals the gap between the pipe flange and the valve disc to provide shut-off. The performance of butterfly valves is heavily dependent on the quality of the seat construction and its ability to seal.

There are several types of end connections that allow for easy installation of these valves, but the most common are lug and wafer style, both fitting between flanges.

Lug style butterfly valves are similar to 3-piece ball valves -they allow adjacent piping to be removed independently. This is achieved by using two different set of bolts, with each attaching the pipe flanges at either end of the valve body. With this connection to the valve, the ends of the pipe sections can be removed and replaced independently. Installation is also fool-proof as the number of lugs make centering the valves easy.

Wafer valves, in contrast to lug style, use only one set of bolts to align the valve and the connecting pipelines. This allows the valve to be installed faster for an experienced installer. They can be more difficult to get centered for the less experienced and the larger valves are more cumbersome to install. Taking the valve out of line is also simpler than a lug style.