Boulton and Watt Steam engine

Steam engine, double-acting beam type, cast iron / wrought iron, made by Boulton and Watt, Birmingham, England, 1785, used at Whitbread's Brewery, London, England, 1785-1887. The vertical cylinder is connected to a separate condensor (in a cooling tank with the air pump) to which spent steam is exhausted and cooled to form water, creating a partial vacuum. The piston, which is pushed up and then down by steam admitted to the cylinder below and then above it, is attached to the overhead beam via a set of 'parallel motion' linkages; this mechanism translates the vertical motion of the piston into the arc-wise motion of the end of the beam. The other end of the beam (which rocks up and down about a fixed pivot through its centre) transfers motion via a connecting rod to the 'planet' gear, which turns the horizontal drive shaft via the 'sun' gear; the names refer to the fact that the planet gear moves around the sun gear, which rotates but does not change position. A large flywheel, which maintains momentum between strokes, is attached to the horizontal drive shaft, which also carries the smaller toothed drive wheel and the governor pulley. The centrifugal governor controls the engine speed via a throttle (butterfly) valve in the steam supply pipe.

Cylinder bore is 635 mm (25 in), piston stroke is 1830 mm (6 ft), flywheel diameter is 4270 mm (14 ft), and the mass of the cast iron beam is 9.2 tonnes. Steam admission to the cylinder is via drop (poppet) valves, and a flap valve opens and closes the pipe between the condenser and the air pump.