a simple valve with a hinge on one side; allows fluid to flow in only one direction | one of the paired hinged shells of certain molluscs and of brachiopods |
| the entire one-piece shell of a snail and certain other molluscs |
| control consisting of a mechanical device for controlling the flow of a fluid |
| device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone |
| a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it |