Draft (boiler)

From TrainSpottingWorld, for Rail fans everywhere

Draft (as related to a fire-tube boiler) is the flow of combustion products going from the firebox, through the boiler and up the stack. Draft may be natural, produced by the rising of the combustion gases in the stack, or by mechanical means, for example a blower. Since the stack of a locomotive is too short to provide natural draft, during normal running forced draft is achieved by directing the exhaust steam from the cylinders through a cone (“blast pipe”) upwards and into a skirt at the bottom the stack. When the locomotive is stationary or in a restricted space “live” steam from the boiler is directed through an annular ring surrounding the blast pipe to produce the same effect.

See also