Description:First Drawing of the 'Small Reciprocating Engine' (Double-acting Engine) by James Watt.
The idea of using steam to push a piston both up and down, thus allowing an engine to make a powered stroke in both directions, was a major development in steam technology. Such engines were called 'double-acting', as steam was being used twice. Watt had considered the idea around the time of the extension of his patent in 1775, and made a drawing which was laid before Parliament. However, the first double-acting engine was not made until 1783. Matthew Boulton encouraged Watt to take up double-acting engines again in 1781, as he could see that it would be needed to produce sucessful rotative engines. Watt included a double-acting engine in his patent of 12th March 1782, and later in the year began designing trial engines for Soho Manufactory. In 1783 an engine with an 18 inch cylinder was set to work powering corn-mill stones. This may also have served as a trial for the Albion Mill. The engine was later used for powering lathes and drills in the engine firm’s workshops. Note that the engine is shown with a rack and sector connection between the piston rod and beam, as Watt had not yet developed the parallel motion. It is also shown with an 'internal' sun and planet gear, with the planet wheel going round the inside of the sun. The first double-acting engine to be sold was that of Coates & Co. in 1784.
This drawing is part of the Archives of Soho collection, which is held by Birmingham City Archives [Ref. MS3147/Portfolio/5/1340]