Rubber Flap Valve

rubber
rubberize: coat or impregnate with rubber; "rubberize fabric for rain coats"
A tough elastic polymeric substance made from the latex of a tropical plant or synthetically
Rubber boots; galoshes
An oblong piece of rubber or similar material embedded in the pitcher's mound, on which the pitcher must keep one foot while delivering the ball
an elastic material obtained from the latex sap of trees (especially trees of the genera Hevea and Ficus) that can be vulcanized and finished into a variety of products
returned for lack of funds; "a rubber check"; "a no-good check"

valve
A membranous fold in a hollow organ or tubular structure, such as a blood vessel or the digestive tract, that maintains the flow of the contents in one direction by closing in response to any pressure from reverse flow
a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it
A cylindrical mechanism in a brass instrument that, when depressed or turned, admits air into different sections of tubing and so extends the range of available notes
A device for controlling the passage of fluid through a pipe or duct, esp. an automatic device allowing movement in one direction only
device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone
control consisting of a mechanical device for controlling the flow of a fluid

flap
(of something attached at one point or loosely fastened) Flutter or wave around
Move (one's arms or hands) up and down or back and forth
roll: move in a wavy pattern or with a rising and falling motion; "The curtains undulated"; "the waves rolled towards the beach"
any broad thin and limber covering attached at one edge; hangs loose or projects freely; "he wrote on the flap of the envelope"
(of a bird) Move (its wings) up and down when flying or preparing to fly
dither: an excited state of agitation; "he was in a dither"; "there was a terrible flap about the theft"