snifting valve

From the noise of its action.

snifting valve (plural snifting valves)

1. (rail transport) A small valve opening into the atmosphere from the cylinder or condenser of a steam engine, to allow the escape of air when the piston makes a stroke.
   • 1946 March and April, “The Why and The Wherefore: Snifting Valves”, in Railway Magazine, page 127:

     The small mounting behind the chimney of many L.N.E.R. locomotives is the "snifting" valve, or vacuum relief valve, provided to keep the superheater elements cool when the engine is running with steam shut off. When the engine is steaming, these valves, which are carried in small chambers connecting with the superheater header, are kept closed by the pressure of the steam; but as soon as the regulator is shut, the valves open, and admit cold air to the superheater pipes. Apart from this provision, the latter, when empty of steam, would be in danger of burning out by the action of the hot gases surrounding them, especially at the firebox end.

• blow valve
• snifter valve
• tail valve