Watt's steam engine diagram

Classic Projects: Watt steam engine

Sir James Watt’s steam engine 250 years on after he produced the first practical and efficient design, which was to play a central role in the Industrial Revolution and the emergence of Great Britain as one of the first modern economic superpowers.

When James Watt was born in the first half of the 18th century, there was nothing new about the steam engine. However, his name will be forever associated with the first practical and efficient design, which was to play a central role in the Industrial Revolution, and the emergence of Great Britain as one of the first modern economic superpowers. When Watt was a boy, early versions of the steam engine were used for pumping water out of mines in the UK’s mineral extraction industry. Look back further into the mists of time and we find that the Ancient Greeks had produced a rudimentary and yet recognisable prototype.

Although he didn’t invent the steam engine, Watt’s improvements were so significant that his name has become the eponym for the machine that shaped the modern world. As with Newton’s early realisations about gravity, Watt’s precise part in the story is now shrouded in myth. What we do know is that at the age of 28, the Scottish instrument maker started to realise the shortcomings of the contemporary Newcomen engine while setting out to repair one, and that his own innovations would lay the claim for the modern machine being Watt’s work.

Arguably, Watt’s greatest improvement over the Newcomen engine was the invention of the separate condenser in 1765, exactly a quarter of a millennium ago. Newcomen engines were incredibly inefficient. Users constantly complained about how much fuel was needed - largely because the steam cylinder needed to be repeatedly heated and cooled, which not only caused inefficiencies, but introduced thermal stress.

Watt’s answer was not to change the way the engine worked, as both versions operated on the principle of a pressure difference created by a vacuum on one side of the piston to push the steam piston down. Instead, he isolated the condenser from the piston chamber, allowing it to remain hot at all times. This, along with other innovations, increased efficiency by a factor of five and reduced the associated consumption of coal by about 75 per cent.

By 1873, Watt had improved on his earlier model and introduced the double-acting rotative type, including centrifugal governor, parallel motion and flywheel. What this meant was that Watt’s machines could now directly drive the rotary machinery of a factory or mill.

But it wasn’t plain sailing for Watt, whose trials were hampered by lack of financial muscle. Enter Matthew Boulton, a venture capitalist whose investment in the project allowed Watt to commercialise his work and eventually retire on its proceeds. By the turn of the century, the company formed by the two men had produced 496 engines and was powering more than 300 mills, generating a total of 11,200 horsepower. Impressive as this might sound, it was a drop in the ocean compared with the total power generated by Britain’s water and windmills - less than 10 per cent of the country’s output. It was also less than half of what the inefficient Newcomen engines were generating in total.

Watt continued his engineering research, venturing into copying machines and chemical engineering. However, it is his work with steam that means his name has been immortalised in the SI unit of power - the watt. His own term, horsepower, contributed to standardising power measurement but is now a ‘supplementary unit’. Despite that, the legend lives on. His portrait graces the current £50 note, and in 2011 he became one of the first seven inductees to the Scottish Engineering Hall of Fame.

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