Number of words – 369

Thomas Newcomen was an iron monger and blacksmith in Devonshire. With a local plumber, John Kelly, Newcomen experimented on a different kind of engine during the first decade of the 18th century. The first successful installation was in Staffordshire in 1712. By 1720, the engine was being widely used, and continuously being improved by the work of engineers and natural philosophers.

What Newcomen introduced should properly be called a steam operated atmospheric engine. A piston in a cylinder was connected to a pivoted beam, whose other end was connected to a long rod that operated conventional lift pump. In the resting position the piston was at the top of its travel. Then the operator opened the valve connecting the cylinder to a steam boiler. Once the cylinder was full of steam, the operator closed the steam valve and opened the valve briefly to admit a jet of cold water. Condensing of the steam would reduce the pressure in the cylinder to atmospheric pressure, forcing the piston down, raising the pump rods and the other end of the beam. A valve at the bottom of the cylinder allowed the water to leave the cylinder. Then the operator opened the steam valve again, atmospheric pressure returned to the cylinder and the weight of the rods forced the piston up in the cylinder. Before long, Newcomen made the action of the valves automatic by attaching them to cams worked by the motion of the beam.

Notice that at no time did pressure exceed atmospheric. The power stroke was provided by the pressure of the outside atmospheric pressure pushing the piston against the reduced pressure within the cylinder. For the return stroke, the force of gravity on the pumping gear lever pushed the piston up.

Newcomen’s engine was greatly superior to Savery’s. In particular, it could be installed at the mine head, with no need to have fire in the mine. However it was an extremely inefficient engine. In the early years, the mechanical work output was only 0.34 % of the energy available in the burning coal. Early engines had a power of only a couple of kilowatts.

Excerpted from ‘Children of Promotheus: A history of Science and Technology’ by James McLachlan