from The Century Dictionary.

  • noun In an engine-cylinder, and particularly on the locomotive engine, a valve which is held shut by steam-pressure when the throttle-valve is open, but which opens by a spring to admit atmospheric air when the throttle is closed and the pistons keep on moving from the momentum of the mass of engine and train.
  • noun In general, a valve designed to control the flow of air. Specifically
  • noun A valve placed upon a steam-boiler to admit air, and thus prevent the formation of a vacuum by the condensation of steam within when the boiler is cooling off, and the consequent tendency to collapse.
  • noun A valve placed at bends and summits of water-pipes, etc., for the outflow of air, as when the pipes are being filled, and for the ingress of air to prevent the formation of a vacuum when the water is drawn out.


Sorry, no etymologies found.



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