Butterfly valves have been around for a long time, and are used for a variety of applications. They made their first appearance during the 1930s, and have been utilized by several industries ever since. Often made out of cast iron, butterfly valve's name is based from the functionality of its disc. There are a few different types of butterfly valves, however, they fall into two basic types - Lug and Wafer valves.
MORE ABOUT BUTTERFLY VALVES
Butterfly valves are classified as "quarter-turn" valves. When the metal disk that's part of the valve’s design is rotated a quarter of a turn, it opens or closes. The disk, referred to as the "butterfly" is attached to a rod. When the butterfly valve is opened all the way, the disc rotates (a 1/4 turn), allowing for a nearly unrestricted passing of the fluid. You can also open the valve gradually to reduce flow. Turning the butterfly (disk), to close the valve, blocks the passage of the fluid. This is due to the disc always being perpendicular or parallel to the flow, resulting in a pressure decrease regardless of the position it is in.
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