valve / valv/ • n. a device for controlling the passage of fluid through a pipe or duct, esp. an automatic device allowing movement in one direction only. ∎  (in full ther·mi·on·ic valve) Electr. British term for thermionic tube. ∎  Mus. 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. ∎  Anat. & Zool. 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. ∎  Zool. each of the halves of the hinged shell of a bivalve mollusk or brachiopod, or of the parts of the compound shell of a barnacle. ∎  Bot. each of the halves or sections into which a dry fruit (esp. a pod or capsule) dehisces.DERIVATIVES: valved adj. [in comb.] a branchiopod has a two-valved outer covering valve·less adj.

valve

valve
1. Any of various structures for restricting the flow of a fluid through an aperture or along a tube to one direction. Valves in the heart (see bicuspid valve; semilunar valve; tricuspid valve), veins, and lymphatic vessels consist of two or three flaps of tissue (cusps) fastened to the walls. The cusps are flattened to the walls to allow the normal passage of blood or lymph, but a reverse flow causes them to block the vessel or aperture, so preventing further backflow.

2. Any of the parts that make up a capsule or other dry fruit that sheds its seeds.

3. One of the two halves of the cell wall of a diatom.

4. Either of the two hinged portions of the shell of a bivalve mollusc.

valve (valv) n. a structure found in some tubular organs or parts that restricts the flow of fluid within them to one direction only (see cusp). Valves are important structures in the heart, veins, and lymphatic vessels (see vein). See also aortic valve, mitral valve, pulmonary (valve), tricuspid valve.

valve (Fr. piston; Ger. Ventil; It. pistone). Mechanism invented c.1813 by the horn-player Heinrich Stölzel and improved in 1818 in collaboration with Friedrich Blühmel, whereby all the notes of the chromatic scale were made available to brass instr. Pitch altered by increasing or decreasing length of tube through which wind must go to produce sound (except normal trombones, for which slide is sufficient). 2 types in use, piston, in which piston works up and down in casing, and rotary, a 4-way stop-cock turning in cylindrical case and governed by a spring. Credit for the first type of valve must go to Charles Clagget, an Irishman, who patented an invention in 1788 which enabled pitch to be altered by means of a lever.

valve
1. One of the two halves of the hinged shell of brachiopods (Brachiopoda), or molluscs (Mollusca) of the class Bivalvia.

2. One half of the cell wall of a diatom.

3. A flap or other constriction that can close to ensure that a fluid flows in only one direction.