TEXT: Steam Engines

Steam was used to provide power for a kind of mechanical toy in ancient times by an ingenious Greek inventor named Hero of Alexandria. But it was not until the end of the seventeenth century that steam was harnessed for machines that could perform work. The development of these machines is usually regarded as the beginning of the Industrial Revolution. The first steam engines were designed for the practical purpose of pumping water out of mines; the first one to be sold commercially was called the Miner's Friend.

When water is boiled it creates a volume of steam greater than the original amount of water. This greater volume can burst a boiler unless it is released. When the vessel is cooled the steam condenses rapidly so that it returns to its liquid state. The result is a partial vacuum in the vessel that contained the steam. It was this vacuum that was put to work by Thomas Savory and later Thomas Newcomer in the earliest practical steam engines.

In the Savory engine steam from a boiler entered a container. When the container was filled cold water was poured over it there­by creating a partial vacuum that sucked water up into the con­tainer. When the container was refilled with steam the water was forced up to a higher level. The valves that controlled the admission of steam to the container as well as the cold water to cause con­densation had to be worked by hand on this engine.

The Newcomer engine was an important advance over the Savory engine. The piston was attached by a chain to a walking beam, a heavy lever that worked on the seesaw principle. The other end of the walking beam was attached to a shaft that worked a pump deep in a mine. When the piston was at the top of the steam-filled cylinder, water was shot into the cylinder condensing the steam. Atmospheric pressure forced the piston down, simultaneous­ly raising water from the mine. Steam was allowed to fill the cylinder and the piston moved up to the top, ready for another stroke.

After the Newcomer engine had been in service for a time, it was discovered that the valves that controlled the steam and cold water could be automated—that is, they could be attached to the walking beam in such a way as to turn them on or off by the action of the beam at certain points during the cycle.

The next important figure in the development of the steam engine was James Watt. He is often credited with being the inven­tor of the steam engine but what he did in fact was improve on the preceding machines. Watt's contributions were of enormous importance in the history of machines and mechanical engineering. One great disadvantage of the Newcomer engine was the amount of fuel it used because so much heat was lost through the alternate heating and cooling of the cylinder. Watt's solution was to separate the cylinder and the condenser so that the cylinder could be kept hot and the condenser cool at the same time. Watt's engine was a great success since it used only one-third as much fuel as the Newcomer engine.

James Pickard, who had been employed by Watt, took t he next big step in the develop­ment of the steam engine. This was to change the reciprocating motion of the piston to rotary motion that could turn wheels. Pickard attached the piston to a connecting rod that turned a crankshaft to produce rotary motion.

Pickard took out a patent on his crankshaft design so Watt had to evolve other devices to produce rotary motion. One of his ideas was the arrangement called sun-and-planet gears. A smaller gear (the planet) rotates around the outer face of a larger gear (the sun).

In these early days of steam engines the technical accomplishments we take for granted were difficult to achieve. Machining of parts was not exact and it was impossible to build boilers that could withstand steam at high pressure. In Watt s day it was the vacuum created by condensing steam that actually performed work. As boiler making improved it was possible to superheat the water and thus increase the steam pressure. This, in combination with safety valves, made steam engines far more effi­cient by putting the pressure to work.

The nineteenth century was the age of steam. The machines of Savory, Newcomer, Watt, and their successors were used not only for pumping water out of mines but for an increasing number of industrial advances. Many early applications were in the man­ufacture of textiles but inven­tors were soon at work on the problem of using steam engines for transportation. By the middle of the century trains with steam powered lo­comotives were becoming the world's most important form of transportation and steam­ships had become common on inland waterways. Before the end of the century the diffi­culties of building trans­oceanic steamships had been solved. Thousands of factories manufacturing hundreds of products used steam power. A familiar sight at the end of the century was the factory or workroom with a whole network of belts that provided drives for oilier devices such as lathes, drill presses, and sewing machines. Thesebelts were a cause of frequent industrial accidents.

By the end of the century the preeminence of steam power was being threatened by two new power sources: electricity and inter­nal combustion. Electric motors come within the field of electrical engineering and will not be discussed at any length in this book. It should be pointed out, however, that they provided greater safety in industrial operations since the shafts and belts used with steam engines were replaced by wires inside walls or under floors. The in­ternal combustion engine will be examined in the following unit.

The twentieth century has seen the displacement of steam from many of its former uses in transportation and industry. We now take for granted the fact that cars are powered by internal combustion engines that burn gasoline. In the early days of the automobile there was experimentation with steam cars; some steam automobiles were even marketed successfully for a number of years. With the world's supply of petroleum now in question there is some renewed interest in steam as one alternate source of energy.

Steam still plays one vital role today in generating electricity. In an electric power plant a turbine drives the shaft of a generator which creates electricity by turning through a magnetic field. In a relatively small proportion of electric plants the turbine is activated by water power; in the majority it is steam that drives the turbine. A blast of steam strikes the blades of the turbine to make them revolve at a high rate of speed.

Even in electric generating plants that use nuclear energy it is steam that actually moves the turbines. The heat released by nuclear fission—the breaking apart of the particles in the center of an atom—is used to boil water. When the water is converted to steam at high pressure it drives the blades of a turbine, just as in a conventional power plant.