Why do steam locomotives "chuff"?

[wva-usa]

As noted on page 297 of the book "A Text-Book of Physics" (pub. 1911), the "chuffing" sound produced by steam locomotives is produced in the smokebox, by the firing of exhaust gases (from each exhaust stroke from the cylinders) through the exhaust pipe (which is actually a nozzle called a blastpipe) into the smokestack.

One of principles of acoustic resonance tells us that the resonance (frequency) of a tube of air is related to the length of the tube and its shape. In general, the larger the (volume of the) smokebox and smokestack, the lower the (fundamental) frequency of the "chuffs" produced by the locomotive. In other words, in general, the "chuffs" produced by small switching locomotive are typically higher in pitch than the "chuffs" produced by a larger locomotive. However, the size of the nozzle opening, the distance of the nozzle from the smokestack's chimney, and other factors will also effect the pitch and timbre of the "chuff" sounds.

 

[EnginneerJoe]

There's more to the boiler than what's being shown. There are a bunch of pipes inside the boiler that the steam runs through, in these pipes the steam is compressed or pressurized. This pressurization is what causes later model steam engines have greater haul, faster speeds, and less water usage. Also, some steamies had water reclamators or condensers on the front or underneath of the boiler assembly. One of the most famous and successful condensers was on the Big Boy. It reclaimed 45% of the used steam from each piston assembly. With 4 piston assemblies that's 100% out of 400% steam usage. Cool huh?