The Newcomen steam engine is one of the most interesting pieces of technology developed during the 1700's. This engine is called "atmospheric engines" because the steam was under only slight pressure. The real driving force of these engines was a vacuum created when steam is condensed back into water. The diagram above explains the principle of operation of a Newcomen engine. In this drawing of a primitive engine (1712), the boiler sits directly below the cylinder. Steam is first admitted from the boiler to the cylinder. When the piston reaches the top, water is sprayed into the cylinder to cool the steam and hence form a vacuum. The piston is sucked down into the cylinder by the weight of the air on top of it and the cycle is started again.

Here is an animation of the Newcomen engine (from http://library.thinkquest.org/C006011/english/jsites/steam_thomas_newcomen.php3%3fv=2)

Source: http://technology.niagarac.on.ca/people/mcsele/newcomen.htm

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Last modified:  Wednesday, February 16, 2005 11:02 AM