""Although the steam that is admitted to the cylinder is hot and dry, it very soon cools and, as it cools, water condenses out. Water is not very compressible, and if enough of it accumulates in the cylinder it may prevent full piston travel. If full-pressure steam is admitted to a cylinder whose piston cannot move properly, there is an excellent chance that this will blow the end of the cylinder off. So cylinders invariably have either safety valves or drain cocks. Drain cocks allow water that has condensed to run out, and are usually operated from the cab by the driver. As most drivers keep the drain cocks open whenever the train is stationary, you'll see a blast of steam from the cylinders as the train comes to a halt, and another blast of steam when it pulls away. Normal practice is to keep the drain cocks open for about six wheel revolutions. "" -[ http://kevinboone.net/steam101_parts.html]
""The world is full of obvious things which nobody by any chance ever observes…""
— Arthur Conan Doyle
“The Hound of the Baskervilles”
""Mathematics...
