Valves are simple machines that are used to regulate the flow of liquid by obstructing a pipe or passageway. They’re found anywhere liquids flow, including indoor plumbing systems—more specifically, your faucet. When you turn the sink handle, out comes water. Turn it back, and it stops flowing. This is the basic job of a valve. They’ve been in use for thousands of years, and are one of the most useful mechanical inventions of all time. Valves are divided into two families—the stop valves, which provide an on, off and partially on setting, and check valves, which only restrict the flow of liquid in one direction.
Butterfly valves are one type of stop valve. The name conjures images of a double-wing shaped insect, right? Well, for whatever reason, the butterfly valve in no way resembles a butterfly. In fact, a butterfly valve is actually composed of a flat, round piece which is supported in the middle that opens or closes when the shaft is rotated. When opened, the edge does provide some resistance to the flow of water. While closed, it perfectly fits the shape of the pipe and provides full obstruction. Because it is able to pivot and stay in more than two positions, the amount of liquid flow can easily be changed as necessary.