Model of a double acting beam type condensing engine

Model of a double acting beam type condensing engine with conical drop valves worked by an eccentric.

The model of a beam engine was preserved by the firm James Watt & Company and represents a rotative engine of moderate size, perhaps one developing about 20 horse power. Several similar models exist, which suggests that they may have been built by apprentices as exercises. Essentially, this is the rotative engine as developed by Watt in the 1780s. However, it has a plain crank, adopted in about 1800 in place of the sun-and-planet gear, and valve-gear with concentric 'socket valves' worked from an eccentric, a feature taken up soon after that. Other improvements of the early nineteenth century include the use of cast iron for the beam, connecting rod and central column of the framing. The plinth under the central column is original but has been altered in its appearance. The present eccentric may be modern although it has the original strap.