In Cornwall the ingression of water was the worst problem in shaft mining. A deep mine is a bit like a water well. You have to pump the water out constantly. The staem engine driving a pump was the answer to allowing deep mining in Cornwall.
By the late 1700s huge beam engines dotted Cornwall. By 1760, most steam engines were of a type developed by Thomas Newcomen . They had a vertical open-topped cylinder inside which a close-fitting piston was hung by a chain attached to a rocking beam. From the other end of the beam, pump rods were attached to a water pump. Steam entered the cylinder at very low pressure, was quickly condensed by a jet of cold water, this created a vacuum. The difference from atmospheric pressure drove the piston down, which in turn raised the pump rods and operated the pump action.
In 1763-4 James Watt, working as instrument-maker for Glasgow University, carried out experiments on a model Newcomen engine and realised that he could improve the fuel efficiency of the Newcomen engine. Watt discovered in 1765, that fuel could be saved by condensing the steam in a separate condenser. This allowed the cylinder to remain at a constant temperature.
This simple innovation reduced the coal consumption of the Newcomen engine by two-thirds. Such a saving was wonderful for a place like Cornwall, where coal had to be expensively transported to operate the steam engines. Watt formed a partnership with Matthew Boulton in 1775 and started to produce his own engines for mine pumping. He then went on to develop a 'rotative' steam engine suitable for driving machinery in factories.
In 1780, James Pickard of Birmingham patented the crank, which converted the vertical motion of the piston into the rotary motion of a flywheel. Watt had to develop an alternative gearing system and made these engines until 1802. These engines could drive the machinery in the textile mills, and represented around 60 percent of the 500 engines built by Boulton and Watt before 1800.
Boulton and Watt found it difficult to keep up with the demand for steam engines. As orders for their engines increased, a shortage of skilled engine erectors meant that engines could not be installed quickly enough. In addition Boulton and Watt offered little after-sales service, so a breakdown could mean a lengthy stoppage. After 1800 the situation improved; Boulton & Watt began to standardise their engine designs and working procedures, making assembly quicker and easier.
James Watt, like the Wright brothers a hundred years later, slowed technological developments by his guarding of his patent rights. However the end of Watt's patent in 1801 allowed local engineers to experiment with further improving the beam engine. The development of the Cornish boiler and high pressure working by Richard Trevithick was significant and the beam engines which emerged in the early part of the 19th century were to power Cornish and Devon mines for the whole of the following century.