Watt Steam Engine - Introduction

Introduction

In 1698, the English mechanical designer Thomas Savery invented a steam pumping appliance that drew water directly from a well by a vacuum, then sent it up to a higher level by steam pressure. The appliance was also proposed for draining mines, but its pumping height was limited, making this impracticable. It consumed a large amount of fuel compared with later engines.

The solution to draining deep mines was found by Thomas Newcomen who developed an "atmospheric" engine also working on the vacuum principle. It employed a cylinder containing a movable piston connected by a chain to one end of a rocking beam that worked a mechanical lift pump from its opposite end. The top of the steam cylinder was open to the atmosphere. At the end of each stroke, steam was introduced into the cylinder below the piston, followed by water. This water condensed the steam and created a partial vacuum below the piston, drawing it down and thus raising the opposite end of the beam.

The Newcomen engine was more powerful than the Savery engine. For the first time water could be raised from a depth of over 150 feet. The first example from 1711 was able to replace a team of 500 horses that had been used to pump out the mine. Seventy-five Newcomen pumping engines were installed at mines in Britain, France, Holland, Sweden and Russia. In the next fifty years only a few small changes were made to the engine design.

While Newcomen engines brought practical benefits, they were inefficient in terms of the use of energy to power them. The system of alternately sending jets of steam, then cold water into the cylinder meant that the walls of the cylinder were alternately heated, then cooled each stroke. As each charge of steam was introduced, it would continue condensing until the cylinder approached working temperature once again. So at each stroke part of the potential of the steam was lost.