The Newcomen atmospheric engine

technology · earth · West Midlands, England

The first steam engine to work reliably as a commercial machine, erected in 1712 by Thomas Newcomen, an ironmonger of Dartmouth, to pump water out of a coal working in the West Midlands. It is not a steam-pressure engine at all: steam fills the cylinder at little above atmospheric pressure, cold water sprayed inside condenses it, and the vacuum lets the weight of the atmosphere drive the piston down. Because the cylinder is heated and chilled on every stroke it wastes almost all the heat put into it, and its thermal efficiency is under one per cent. That did not matter, and understanding why is the point of the machine: it was installed at pitheads, where fuel was the waste product lying on the ground, so an engine that ate coal to raise water that let miners cut more coal was profitable at any efficiency. Several hundred were at work in Britain before Watt's improvements, and the design continued to be built long after, because where coal was free the more economical engine was not worth its higher first cost.