valve

any device that shuts off, starts, regulates, or controls the flow of a fluid

anatomy a flaplike structure in a hollow organ, such as the heart, that controls the one-way passage of fluid through that organ

Also called: tube.�� vacuum tube.��an evacuated electron tube containing a cathode, anode, and, usually, one or more additional control electrodes. When a positive potential is applied to the anode, electrons emitted from the cathode are attracted to the anode, constituting a flow of current which can be controlled by a voltage applied to the grid to produce amplification, oscillation, etc See also diode triode tetrode pentode

zoology any of the separable pieces that make up the shell of a mollusc

music a device on some brass instruments by which the effective length of the tube may be varied to enable a chromatic scale to be produced

botany

1. any of the several parts that make up a dry dehiscent fruit, esp a capsule

2. either of the two halves of a diatom cell wall

archaic��a leaf of a double door or of a folding door

Any of various structures that prevent the backward flow of a body fluid, such as blood or lymph. Valves in the heart, veins, and lymphatic vessels contain flaps (known as cusps) that close in response to pressure created by the backflow of fluid.

One of the paired hinged shells of certain mollusks, such as clams and oysters.

See electron tube