How do steam locomotives work?
A steam locomotive needs water, fuel (coal or fuel oil) and fire. The fuel is burnt in the firebox (a kind of furnace) (1). The hot air (combustion gas) that this produces flows through pipes in the boiler and heats the water to over 205 degrees (2). This creates wet steam (3). The wet steam is heated again to 420 degrees via the distribution box through superheater coils (4) and fed into the slide valve (5). The incoming steam (6) creates so much pressure that the pistons connected to the driving rods (7) set the crankshaft and thus the gear wheel in motion. The steam locomotive moves. The spent steam is led out through the chimney (8). This produces the typical puffing, wheezing and blowing. When going downhill, the steam engine is operated as an air pump (counter-pressure brake), it brakes the whole train. In addition, the steam brake and hand brake provide extra safety.