General English

General Science

  • noun a flap in the heart, blood vessels or lymphatic vessels or other organs, which opens and closes to allow liquid to pass in one direction only


  • noun a mechanical device for controlling the flow of a fluid

Cars & Driving

  • noun any device that starts, stops, regulates or controls the flow of a fluid, gas, etc.
  • noun a valve which opens the respective ports during the induction and exhaust strokes and seals the compression chamber during the compression and expansion strokes
  • symbolV


  • Device that regulates a liquid or gas flowing through piping.


  • An active device consisting of a hermetically sealed envelope within which electrons are conducted between electrodes. The cathode is the source of electrons, the positive electrode to which they travel is the anode or plate, while other electrodes that may be present include control grids and screen grids. electron tubes may or may not contain a gas, and its presence and concentration affects the characteristics of said tubes. Such tubes have many applications, including their use in amplification, modulation, rectification, and oscillation. There are many examples, including CRTs, phototubes, pentodes, mercury-vapor tubes, and so on. When such a tube is evacuated to a degree that any residual gas present does not affect its electrical characteristics, it is called vacuum tube. Better known as electron tube, or tube (1).

Origin & History of “valve”

The etymological notion underlying valve is of a door opening and closing. The word was adapted from Latin valva, which denoted one of the sections of a folding or revolving door, and may have had links with volvere ‘roll’ (source of English revolve). It carried its original meaning with it into English, but it was not used at all widely until various metaphorical senses, such as ‘flap controlling the flow of a fluid’ and ‘half of a shell’, evolved. The electronic valve is so called because current can flow in only one direction through it; the usage dates from the early 20th century.