1A device for controlling the passage of fluid or air through a pipe, duct, etc., especially an automatic device allowing movement in one direction only.

1. 1.1British Electronics
   short for thermionic tube

   Example sentencesExamples

   • Unlike delicate solid-state circuitry, valves are incredibly robust from an electrical perspective.
   • Equipped with transistors instead of valves, it could be operated for 80 hours on four hearing aid batteries, costing 2s 6d each.
   • You could even build a functional, if somewhat cumbersome, guitar amplifier with a hydraulic system replacing transistors or valves.
   • Silicon chips transformed the then slowly evolving world of electrical circuits and valves to the vibrant and fast developing world of electronics.
   • Electronic valves are no longer used and have been replaced by transistors and diodes which have a low current consumption, greater reliability and much smaller dimensions.
2. 1.2Music 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.
   〔乐〕（铜管乐器的）阀键
   Example sentencesExamples

   • The later introduction of valves extended the versatility of brass instruments to cover the full chromatic scale.
   • For trumpeters the left hand acts merely as a clamp holding the instrument whilst the three valves are operated by fingers of the right hand.
   • The soloists played on natural horns, instruments that have no valves and are not as powerful as their modern descendants.
3. 1.3Anatomy Zoology 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.
   〔剖，动〕瓣膜，瓣
   Example sentencesExamples

   • Veins become varicose when valves in the veins closest to the skin's surface don't function correctly.
   • During pregnancy, hormones relax the muscles in your digestive tract, including the valve in the esophagus.
   • If the heart valves can't open and close correctly, blood can't flow smoothly.
   • The condition results from problems with valves in the veins of the leg.
   • When crocodiles are completely submerged, the ears and nostrils are closed by valves, and the eyes covered by membranes.
4. 1.4Zoology 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.
   〔动〕壳板
   Example sentencesExamples

   • The brachiopods from the limestone unit are mostly preserved as shells, most with valves conjoined.
   • The two shell valves would have been rigidly fixed in place, and the dorsal margin could not have been more than a poorly elastic structure, if that.
   • Note that each shell valve is symmetrical about the midline, but the two shell valves are often unequal in size.
   • All these plates that attach to the floor of the brachial valve may have been thickened by secondary overgrowth.
   • The remains usually consisted of a large piece of one valve plus a fragment of the other valve attached by a virtually intact hinge.
5. 1.5Botany Each of the halves or sections into which a dry fruit (especially a pod or capsule) dehisces.
   〔植〕裂爿
   Example sentencesExamples

   • The fruit is a small oblong capsule with two valves containing many small seeds.
   • The brush-like hairs at the end of the anther tube are not bent, and they enclose the valve.
   • As the pollinator pushes back the brush-like hairs, the valve opens releasing the pollen onto the back of the pollinator.
   • Fruits were harvested just prior to dehiscence of the capsule valves.
   • Dehiscence of the anther valves begins at the distal end.