Steam engine

A steam engine is a machine  that produces  mechanical work using steam. It needs a hot source to  transform water into steam. On the left, a simple steam engine. There is an inlet valve ( in the middle )   and two Outlet valves.

Below this valves, there is a Fp ( front port ) and a Bp ( Back port) allow high-pressure steam to act alternately on both faces of the piston.

Phases in a Steam engine

Phase a ) The opening of the front port allows superheated steam from the boiler to enter the cylinder and push the piston back. As the piston move backwards, used steam from the previous stroke is exhausted through the back port.

Phase b). The valve starts to move backwards while the steam in the cylinder continues to expand and pushes the piston back.

Phase c) The front port opens to exhaust steam and at the same time the back port closes. This creates some back pressure before the next stroke is made.

Phase c) The back port opens  to allow “fresh” steam into the cylinder which then push the piston forward. A new sweep begins again and the process repeats

As you may appreciate on Figure c, there is a brief  time that both valves are close. The rest of time, the exhaust steam, just  vents out into the air. It explains why old fashioned trains  have to take on water from deposits from time to time.

The intermittent  realise of steam also explains the famous ” choo, choo, choo”.  When the Fp or the Bp valve opens  the steam exhaust escapes under a great  pressure and makes a “choo!” sound. When Fp and Bp valves are closed, no steam is realise and no sound is produced. Later, the “choo” sound come back as a consequence of another pressured steam realise.

As faster the train moves, as more continuously the sound is.

The boiler

A boiler is a essential  component in all type of steam engine. The high-pressure steam needed to move the piston in  a steam engine comes from a boiler. Its job is to apply heat to water to create high-pressure steam.

The following  diagram shows you a typical  water-tube boiler. In this boiler, water flow through a rack of pipes that are placed in the path of hot gases from the fire.