How does steam power steam trains?

Answer 1

Believe it or not, all that hard work shovelling coal into a blazing furnace, those mighty towers of smoke and ash, and all those beautiful mechanical joints moving at mighty speed, is just to turn water into steam. Mind you - lots of steam.

When coal is thrown into that hole on the footplate of the train, it falls into the 'firebox' to burn at a phenomenal rate. The locomotive boiler is basically a drum filled with water. Tubes, called firetubes, run through the boiler full of hot gases generated in the firebox. It is these gases which transfer heat to the water to generate steam. The top portion of the boiler is where the steam is collected in what is called the dome. This steam runs through pipes to the front of the locomotive, and is injected into the cylinders, the incredible pressure generated pushes a piston forwards. This piston is connected to the drive wheels, and they begin to turn and move the train forwards. This process, accelerated and repeated over and over again, pushes the train onwards.

The used steam is taken out of the cylinder, and ejected out into what is known as the blastpipe located in a drum shaped space at the front of the engine called the smokebox. it is then ejected into the atmosphere through the chimney. The blast generated aids the passage of hot gases through the firetubes. The vacuum created in the smokebox was in some countries at one time, used for braking on the engine and its train.

There two ways to control the speed of the train, the first is a stopcock in the cabin called the regulator which controls the steam pressure applied to the cylinders. When the regulator is shut there no steam gets to the cylinders and the engine stops. The second is called the "cut-off" is more of a power control which uses the expansive properties of steam. The steam is "cut-off" before the piston reaches full stroke allowing the steam to expand. Early or short cut-offs are used when the engine is travelling at speed. Late or long cut-offs when the engine is moving slowly perhaps when slogging up a steep gradient.

I might add that some of the larger American-made steam locomotives were equipped with mechanical stokers. A screw elevator would feed coal into the firebox. The fireman would turn a control valve that would send steam to a motor connected directly or indirectly to the two screw augers. As the coal exited the augers it would be slung through the firebox. This allowed for even burning of the coal.

George Stevenson disccovered the effect of steam, by watching a kettle boil, as a young man. Realising that water expanded, when heating to steam, he realsied, experimented and found that steam expands with enormous power.