Newcomen Steam Engine - Successor

Successor

The main problem with the Newcomen design was that it was very expensive to operate. After the cylinder was cooled to create the vacuum, the cylinder walls were cold enough to condense some of the steam as it was admitted. This meant that a considerable amount of fuel was being used just to heat the cylinder back to the point where the steam would start to fill it again. As the heat losses were related to the surfaces, while useful work related to the volume, increases in the size of the engine increased efficiency. Newcomen engines became larger in time. However, efficiency did not matter very much within the context of a colliery, where coal was freely available.

Newcomen's engine was only replaced when James Watt improved it in 1769 to avoid this problem (Watt had been asked to repair a model of a Newcomen engine by Glasgow University. A model exaggerated the scale problem of the Newcomen engine). In the Watt steam engine, condensation took place in a separate container, attached to the steam cylinder via a pipe. When a valve on the pipe was opened, the vacuum in the condenser would, in turn, evacuate that part of the cylinder below the piston. This eliminated the cooling of the main cylinder, and dramatically reduced fuel use. It also enabled the development of a double-acting cylinder, with upwards and downwards power strokes more suited to transmitting power to a wheel.

Watt's design, introduced in 1769, did not eliminate Newcomen engines immediately. Watt's vigorous defence of his patents resulted in the desire to avoid royalty payments as far as possible.

The expiry of the patents led to a rush to install Watt engines in the 1790s, and Newcomen engines were eclipsed, even in collieries.