| The powering force for this engine was from two open-ended cylinders one positioned directly above the other. Thompson had reverted to the principles first used in 1712 and pioneered by Thomas Newcomen. This engine at Arnold was a double acting atmospheric engine, each cylinder was filled in turn with steam and, after the water spray a vacuum was formed, which drew each piston through a powered stroke. The upper piston pushed the main beam up and, the lower piston then pulled it down again. |
| When the mill at Arnold was built in 1790, the only drive to the spinning machines was from the waterwheel. With the outbreak of the Napoleonic Wars the demand for worsted increased and the factory started to work twenty four hours per day to supply the increased demand. However, after two and a half days working the mill pond was empty. The engine was then used for the remainder of the week, allowing the mill pond to refill. |  |
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This engine at Arnold was made to enormous proportions,
from the floor level to the top of the main beam measured 42 feet. The assembled cylinders had an overall height of 23 feet. The bore of each cylinder was 40 inches with a working stroke of six feet. This engine only worked from 1797 until 1810, and the mill at Arnold was then demolished. In 1811 and the engine was broken up and sold for scrap. |
The remaining information needed to make the model was gathered together by studying all that is known about Francis Thompson, who also made many of the engines which were used in the Derbyshire lead mines. Only eight rotary atmospheric engines were made by Thompson, and the one at Arnold is the largest he ever made. For demonstration purposes the model can be seen working as it would have originally done in 1797, it is the only working double acting atmospheric rotary beam engine in the world.
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