From the perspective of the 21st century the steam engine invented by Thomas Newcomen (1663-1729) of Darmouth seems pathetically primitive, particularly after its replacement with the steam engine of James Watt. But in its time the Necomen engine was a major technological advance. There had been steam power devices before Newcomen, some going back to the time of the ancient Greeks but these were toys and gadgets without practical uses. Others that were not toys were laboratory models not suitable for industry. The closest anyone came to creating a real working steam engine was the device created by Thomas Savery. Savery's engine could lift water but only a distance of fifty feet and could not operate continuously. The most pressing need for an engine was to pump water from the deep mines. This the Savery engine could not do but the Newcomen engine could.
The Savery engine operated using a boiler that would through steam pressure lift water up to about thirty feet. The higher pressures required to lift water higher created too much strain on the boiler and the temperatures required to get those pressures melted the solder in the joints of the equipment. When the boiler's load of water had been forced up the pipes the valve was closed and another valve opened which was connected to a pipe immersed in water about twenty feet below the boiler. The fire under the boiler was put out. As the boiler cooled a vacuum was created in the boiler which sucked up water through the connecting pipe. More correctly the vacuum in the boiler resulted in the atmospheric pressure pushing water up the pipe and into the boiler. There is a theoretical limit of about 32 feet for distance water can be lifted by a vacuum and a practical limit of about twenty feet due to the imperfection of the vacuum and the connections. This was not nearly enough for the deep copper, tin and coal mines of England. The time required for the boiler to cool meant the pumping rate was severely limited.
The Savery steam engine could not be improved to solve the problem of water pumping. A new design and principle of operation was required.
Thomas Newcomen provided that design. Newcomen was a merchant, an iron monger who dealt in metal parts and bulk iron. He dealt with the needs of the mines in southwest Britain and knew of need for pumps in the deep mines. He also fabricated equipment for his customers. His assistant and partner, Cawley, was a plumber. Between the two of them they uniquely had the skills required to fabricate a pump operated by steam power. Other more learned men attacked the problem but did not have the practical skills that Newcomen had. In effect, Thomas Newcomen was a businessman-engineer, just what was needed to solve the problem.
The way the Newcomen engine work, as is illustrated below, what with a piston in a cylinder connected to a rocker arm attached to a pump. first the cylinder was filled with steam from a boiler. This pushed the piston up. Then water was sprayed into the cylinder creating a vacuum. This pushed the piston down pulling the pump rod on the other side of the rocker arm up, thus lifting the water.
The opening and closing of valves for the alternating injection of steam and water was self-actuating so the engine and pump could operate continuously.
The Newcomen engine solved the problem of pumping water from the deep mines. Despite a high cost of £1000 about 1500 were put into operation. Many of these Newcomen engines were built after the invention of the Watt engine.