Following a summer in which we have commemorated 50 years since the end of British Railways main line steam, Brian Sharpe looks back to the beginnings of steam traction. In the first of a new series, he investigates the background to how the position of chief mechanical engineer came about in the early days of steam power – leading to the evolution of steam locomotive design.
The beginnings of the steam age were 100 years earlier than the first railway locomotives – in 1712, when Thomas Newcomen invented the atmospheric engine, the first practical device that used steam power to perform mechanical work.
The Newcomen engine was a stationary machine that was used mainly for pumping water out of mines. It operated in the opposite way to the accepted manner of the steam locomotives that were eventually developed from it, by condensing steam drawn into the cylinder and creating a partial vacuum that allowed the atmospheric pressure to push the piston into the cylinder.
Hundreds of Newcomen engines were constructed during the 18th century for use throughout Britain and Europe.
Attempts were made to drive machinery by Newcomen engines by converting the vertical motion into rotary motion, but these were unsuccessful, as the single power stroke produced a very jerky motion.
James Watt later improved on Newcomen’s design and roughly doubled its fuel efficiency. He made the condenser separate and reduced heat loss, while at the same time making the cylinder double-acting.
Many atmospheric engines were then converted to the Watt design and he usually gets the credit for having designed the steam engine.
Richard Trevithick, born in Cornwall in 1771, was heavily involved in mining and engineering from an early age.
His most significant contribution was the development of the first ‘high-pressure’ steam engine.
He was not the first to think of using steam at a pressure of about 30psi. William Murdoch had developed and demonstrated a model steam carriage as early as in 1784 and he demonstrated it to Trevithick in 1794.
As his experience grew, Trevithick realised that improvements in boiler technology permitted the safe production of high-pressure steam that could move a piston in a steam engine on its own account, instead of using pressure only just above atmospheric in a condensing engine.
Not only would a high-pressure steam engine eliminate the condenser, but it would allow the use of a smaller cylinder, saving space and weight.
He even thought that his engine could now be so much lighter and more compact that it could be small enough to move its own weight, even with a carriage attached.
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