David Hulse displayed this model of the Arnold Mill Engine at the Midlands Model Engineering Exhibition, where he regularly displays his fine models.

This engine was designed by Francis Thompson an engineer from Ashover, Derbyshire in 1797, to drive a worsted mill in Arnold, Nottingham in a way to avoid any patent litigation with Boulton and Watt. Power was supplied from two open-ended cylinders one positioned directly above the other. Thompson had reverted to the principles first used in 1712 by Thomas Newcomen in this design.

The engine was double acting, each cylinder was filled in turn with low pressure steam at 3psi and, after a spray of cold water a vacuum was formed, which drew each piston in turn through a powered stroke, with the upper piston pushing the main oscillating beam vertically  and the lower one pulling it down again. 

When the Arnold mill was built in 1790, the only drive to the spinning machines was from an undershot water wheel. With the outbreak of the Napoleonic Wars demand for worsted cloth increased and the factory started to work round the clock. However, the mill pond would empty after two and a half days working and the engine was used for the remainder of the week, allowing the millpond to refill. 

This engine at Arnold was huge. From the floor level to the top of the main beam measured 42’ and the assembled cylinders were 23’ high. The bore of each cylinder was 40” with a working stroke of six feet.

This engine worked from 1797 until 1810, when the mill was demolished and the engine broken up for scrap.

More details of David’s outstanding models are at http://www.davidhulse.co.uk