Description

A 1/2 inch scale model of a James Watt’s industrial rotative condensing beam engine, modelled from the engine built by Boulton and Watt in about 1786-8 and erected in a Birmingham works for driving machinery used for lapping or polishing ornaments, where it became known as the "lap" engine, continuing to work until 1858. The model was built by E.C. Roderick, Bedford, over a period of two years - a triumph with regard to the almost impossible difficulties connected with achieving Watt valve gear working on so small a scale as 5-10 psi. The gunmetal cylinder is 7/8 inch bore by 2-inch stroke correctly mounted. The valve gear consists of a group of four poppet valves, two admission and two exhaust (full stroke admission), controlled through the condensing air pump plug rod. Tappets engage with the keyed handling arms alternately rotating the exhaust and the admission cross shaft. A third shaft, situated between them, carried a double ended latch, the ends shaped with toe pieces. As the tappets act on the handling arms in turn, detent levers on the cross shafts engage with the latch, locking on end and releasing the other alternately. The locking of each shaft holds the valves in a closed position, whilst the shaft that is released is caused to revolve by means of the weights, opening the valves. Further details include a working jet condenser and air pump, chain driven working Watt governor, sun and planet gear connection between connection rod and main shaft, wooden frame with correct square and hexagon headed coach bolts, wooden toothed eight-spoke flywheel and Watt parallel motion.