Model (Scale 1:8) of a semi-portable overtype engine made by Robey & Co. The idea of a portable steam engine became practicable with the introduction of high-presure non-condensing engines, pioneered by the Cornish engineer Richard Trevithick (1771-1833) in 1802. This type of engine was quite easily transported (being self-contained) and needed practically no foundations. However, not being mounted on wheels it was intended for more permanent situations than the fully portable engine. It is called an 'Overtype' engine as the cylinder is mounted on top of (or over) the boiler.
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