is a device that regulates the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. http://www.bolev-hydraulics.com/Xinwenzhongxin/

A door; especially, one of a pair of folding doors, or one of the leaves of such a door.

A lid, plug, or cover, applied to an aperture so that by its movement, as by swinging, lifting and falling, sliding, turning, or the like, it will open or close the aperture to permit or prevent passage, as of a fluid.

One or more membranous partitions, flaps, or folds, which permit the passage of the contents of a vessel or cavity in one direction, but stop or retard the flow in the opposite direction; as, the ileocolic, mitral, and semilunar valves.

One of the pieces into which a capsule naturally separates when it bursts.

A small portion of certain anthers, which opens like a trapdoor to allow the pollen to escape, as in the barberry.

one of the segments produced by the splitting of a ripe capsule ( q.v.)

one of the portions into which a capsule separates when ripe.

One of the two similar portions of the shell of a diatom.

One of the pieces or divisions of bivalve or multivalve shells.

One of two, usually identical, more or less flattened and ornamented, plates.

one of the two halves of the shell of a bivalve mollusk

Glass tube which amplifies sound using a cathode and anode.

The original device used to amplify an audio signal consisting of electrodes in a sealed, gas filled glass tube. Now found on some high end amplifiers, they produce a warm, involving sound.

Short for Thermonic Valve, or in Britain, electron tube. - Category: Recording

glass tube which amplifies sound (signal), very much like the modern day transistor.

or vent - opening in the top (or, in some models, sides) of the balloon through which hot air can be released to initiate a descent or a landing.

A move which simultaneously opens one line of play while closing another.

These open or close to admit air to the pipe. Their movement is controlled through the keys on the keyboard. Pressing a key down pulls the valve open. Each key has a spring underneath it so that the key returns to the "up" position, allowing the valve to close.