Butterfly valve

[1] A small metal disc located in the carburetor that controls the flow of air into the carburetor. It is so named due to its resemblance to the insect of the same name.
[2] A disk turning on a diametral axis inside a pipe; used as a throttle valve in a gasoline engine.
[3] A valve consisting of a pair of semicircular plates hinged to a common diametral spindle in a pipe; by hinging axially, the plates permit flow in one direction only.