Concentric Butterfly Valve

butterfly valve
a valve in a carburetor that consists of a disc that turns and acts as a throttle
A valve consisting of a disk rotating on an axis across the diameter of a pipe to regulate the flow, as in the throttles of many engines
A valve consisting of a pair of semicircular plates that are attached to a spindle across a pipe and hinged to allow flow only one way
A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off.
(Butterfly Valves) A valve consisting of a cylindrical body with a rotating vane to control flow. Tight Shutoff is obtained by an elastomer body liner into which the vane seats.

concentric
having a common center; "concentric rings"
Having a common center; (of a motion) in the direction of contraction of a muscle. (E.g. extension of the lower arm via the elbow joint while contracting the triceps and other elbow extensor muscles; closing of the jaw while flexing the masseter)
Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another. Concentric objects generally have different radii, as concentric objects with the same radius are equal.
Of or denoting circles, arcs, or other shapes that share the same center, the larger often completely surrounding the smaller