The High Pressure Engine
As his experience grew, he realised that improvements in boiler technology now permitted the safe production of high pressure steam, which could move a piston in a steam engine on its own account, instead of using pressure near to atmospheric in a condensing engine.
He was not the first to think of so-called "strong steam". William Murdoch had developed and demonstrated a model steam carriage, starting in 1784, and demonstrated it to Trevithick at his request in 1794. In fact, Trevithick lived next door to Murdoch in Redruth in 1797 and 1798. Oliver Evans in the U.S. had also concerned himself with the concept, but there is no indication that his ideas had ever come to Trevithick's attention.
Independently of this, Arthur Woolf was experimenting with higher pressures whilst working as the Chief Engineer of the Griffin Brewery (proprietors Meux and Reid). This was an Engine designed by Hornblower and Maberly, and the proprietors were keen to have the best steam engine in London. Around 1796, Woolf believed he could save substantial amounts of coal consumption.
According to his son Francis, Trevithick was the first to make high pressure steam work in England in 1799. 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 reasoned that his engine could now be more compact, lighter and small enough to carry its own weight even with a carriage attached. (Note this did not use the expansion of the steam, so-called "expansive working" came later).
Read more about this topic: Richard Trevithick
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