Valves are fluid flow control devices used in a variety of industries. There are many different types of valves, with two major categories being multi-turn valves (typical home water faucet as an example) and quarter-turn valves (typical gas shut off on a home furnace as an example). This article deals with a butterfly valve, a quarter turn type valve, depicted in Figure 1. A butterfly valve incorporates a circular disk that when rotated perpendicular to the long axis of the pipe blocks the flow of fluid (Figure 1A). The valve handle indicates this condition when it is placed perpendicular to the long axis of the pipe. When the disk is parallel to the long axis of the pipe (Figure 1B), it offers little resistance to fluid flow. The handle is parallel to the water pipe indicating wide open and maximum flow. The butterfly valve can act as a control valve with the handle in intermediate positions.

Figure 1 - Valve handle

Figure 1

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