III.

Fire-Tube Boiler

Savery, Watt, and Newcomen engines all operated at pressures only slightly above atmospheric pressure. In 1800 the American inventor Oliver Evans built a high-pressure steam engine utilizing a forerunner of the fire-tube boiler. Evans's boiler consisted of two cylindrical shells, one inside the other; water occupied the region between them. The fire grate and flue were housed inside the inner cylinder, permitting a rapid increase in steam pressure. Simultaneously but independently, the British engineer Richard Trevithick developed a similar “Cornish” boiler. The first major improvement over Evans's and Trevithick's boilers was the fire-tube “Lancashire Boiler,” patented in 1845 by the British engineer Sir William Fairbairn, in which hot combustion gases were passed through tubes inserted into the water container, increasing the surface area through which heat could be transferred. Fire-tube boilers were limited in capacity and pressure and were also, sometimes, dangerously explosive.