Smeaton's improvments on Newcomen steam engines

Mr. Smeaton's improvements on Newcomen's engine consisted only in proportioning its parts, but without altering anything in its principle : it was still Newcomen's, though perfected [1].

The renowned engineer Mr. John Smeaton conducted research on the Newcomen steam engine around the year 1772, just as he had previously done with regard to water and windmills. He started in 1765 in Austhorpe, near Leeds, with an experimental steam engine that had a cylinder of 10 inch diameter and a 38 inch stroke. In an engine which he constructed for the New River Co. at River Head Islington, in 1767, he put his ides into practice but found that they did not answer his expectations. He accordingly went to work systematically, with the aid of William Brown of Throckley, and obtained from him a list with about 100 engines, mainly in the North of England. He also collected particulars of eighteen large engines in Cornwall. Based on this data he designed and superintended the construction of quite a number of engines. [2]

While not adding anything to Newcomen's invention, he did establish proportions for engines of all sizes and their performance, allowing him to select the ideal dimensions for a given requirement. Although not an inventor his systematic research is the typical approach of an engineer. He created many of these very large engines after experimentally determining the right proportions and improving on details to reduce friction and reducing leakage of the piston. For instance Smeaton built an improved boring mill at Varon Iron Works to built the cylinder with improved precision [3]. But Smeaton also had an eye on preventing heat losses.

Smeaton constructed his engines with steam cylinders that had longer strokes than were used before and gave them such lengths that he could substantially enhance the piston's speed by applying a bigger excess of steam pressure. [4] Smeaton enhanced the effect of condensation by allowing the water to flow in at a greater speed. The piston was provided with an oil-soaked hemp pack and was covered with about 60mm thick wooden planks at the bottom to prevent premature condensation of the steam. The injection tube was, as far as it was in the cylinder, protected by wood cladding against excessive heating. Through the center of the balancier went a cast-iron axle, whose pins were mounted in gun metal (red brass) casting blocks, which were suitably drilled.

The first of Smeaton's new design of engines was built in 1774, at Long Benton, not far from Newcastle upon Tyne. [5]. The cylinder of this atmospheric machine that delivered approximately 40 horse powers had a diameter of 1320 mm and the stroke was 2100 mm. Before the conversion of the machine carried out by Smeaton, the steam engine made 7¾ strokes per minute, and after the conversion 12 strokes per minute. The mentioned measures had improved the coal consumption in relation to the same power by the factor 2.19 (!). [6]

The performance of the engines built by Smeaton was far superior to the common type of engines that were typically made before his time [6]. The Smeaton steam engines survived long after the introduction of the Watt steam engines in places where coal was cheap to get. One of the largest of the steam engines built by Smeaton was the one at the Chacewater Pit in Cornwall, built in 1775. The cylinder had a diameter of 1.82m and weighed 6600 kg, the stroke was 3m. This steam engine delivered around 80 horse powers. The balancier was composed of 20 beams of fir wood, was 8.3m long and 1.8m high in the middle. The axle around which it moved was 210mm in diameter. The axle was mounted in drilled bronze blocks, which in turn were mounted in thick granite blocks. [7]