any device that shuts off, starts, regulates, or controls the flow of a fluid
anatomya 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 tubean 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, etcSee also diode (def. 2), triode (def. 1), tetrode, pentode
zoologyany of the separable pieces that make up the shell of a mollusc
musica device on some brass instruments by which the effective length of the tube may be varied to enable a chromatic scale to be produced
any of the several parts that make up a dry dehiscent fruit, esp a capsule
either of the two halves of a diatom cell wall
archaica leaf of a double door or of a folding door
late 14c., "one of the halves of a folding door," from Latin valva "section of a folding or revolving door," literally "that which turns," related to volvere "to roll" (see volvox). Sense extended 1610s to "membranous fold regulating flow of bodily fluids;" 1650s to "mechanical device that works like a valve;" and 1660s in zoology to "halves of a hinged shell."
Any of various mechanical devices that control the flow of liquids, gases, or loose material through pipes or channels by blocking and uncovering openings.
The movable part or element of such a device.
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.