Watt, James

James Watt, FRS, FRSE (19 January 1736 – 25 August 1819) was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.

While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. He realised that contemporary engine designs wasted a great deal of energy by repeatedly cooling and re-heating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. Eventually he adapted his engine to produce rotary motion, greatly broadening its use beyond pumping water.

Watt attempted to commercialize his invention, but experienced great financial difficulties until 1775 he entered a partnership with Matthew Boulton. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none were as significant as his steam engine work. He died in 1819 at the age of 83. Watt has been described as one of the most influential figures in human history.

He developed the concept of horsepower and the SI unit of power, the watt, was named after him.

Early experiments with steam

In 1759 Watt's friend, John Robison, called his attention to the use of steam as a source of motive power. The design of the Newcomen engine, in use for almost 50 years for pumping water from mines, had hardly changed from its first implementation. Watt began to experiment with steam though he had never seen an operating steam engine. He tried constructing a model. It failed to work satisfactorily, but he continued his experiments and began to read everything he could about the subject. He came to realize the importance of latent heat in understanding the engine, which, unknown to Watt, his friend, Joseph Black, had previously discovered some years before. Understanding of the steam engine was in a very primitive state, for the science of thermodynamics was not in place for another 100 years or so.

In 1763, Watt was asked to repair a model Newcomen engine belonging to the University. Even after repair, this engine only barely worked. After much experimentation, Watt demonstrated that about three quarters of the heat of the steam was being wasted - consumed in heating the engine cylinder on every cycle. This energy was wasted because later in the cycle, cold water was injected into the cylinder to condense the steam to reduce its pressure. Thus the engine expended much of its energy in repeatedly heating the cylinder rather than in delivering mechanical force.

Watt's critical insight, arrived at in May 1765, was to cause the steam to condense in a separate chamber apart from the piston, and to maintain the temperature of the cylinder at the same temperature as the injected steam (by surrounding it with a "steam jacket"). This meant that very little heat was absorbed into the cylinder itself on each cycle, and thus more heat from the steam was made available to perform useful work. Watt had a working model later that same year.

Despite a potentially workable design, there were still substantial difficulties in constructing a full-scale engine. This required more capital, some of which came from Black. More substantial backing came from John Roebuck, the founder of the celebrated Carron Iron Works, near Falkirk, with whom he now formed a partnership. Roebuck lived at Kinneil House in Bo'ness, during which time Watt worked at perfecting his steam engine, in a cottage adjacent to the house. The shell of the cottage, and a very large part of one of his projects, still exist to the rear.

The principal difficulty was in machining the piston and cylinder. Iron workers of the day were more like blacksmiths than modern machinists and were unable to produce the components with sufficient precision. Much capital was spent in pursuing the ground-breaking patent on Watt's invention. Strapped for resources, Watt was forced to take up employment first as a surveyor, then as a Civil engineer for eight years.

Roebuck went bankrupt, and Matthew Boulton, who owned the Soho Foundry works near Birmingham, acquired his patent rights. An extension of the patent to 1800 was successfully obtained in 1775.

Through Boulton, Watt finally had access to some of the best iron workers in the world. The difficulty of the manufacture of a large cylinder with a tightly fitting piston was solved by John Wilkinson who had developed precision boring techniques for cannon making at Bersham, near Wrexham, North Wales. Watt and Boulton formed a hugely successful partnership (Boulton and Watt), which lasted for the next twenty-five years.

First engines

In 1776, the first engines were installed and working in commercial enterprises. These first engines were used to power pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft. The design was commercially successful, and for the next five years Watt was very busy installing more engines, mostly in Cornwall for pumping water out of mines.

These early engines were not manufactured by Boulton and Watt, but were made by others according to drawings made by Watt, who served in the role of consulting engineer. The erection of the engine and its shakedown was supervised by Watt, at first, and then by men in the firm's employ. These were large machines. The first, for example, had a cylinder with a diameter of some 50 inches and an overall height of about 24 feet, and required the construction of a dedicated building to house it. Boulton and Watt charged an annual payment, equal to one third of the value of the coal saved in comparison to a Newcomen engine performing the same work.

The field of application for the invention was greatly widened when Boulton urged Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling. Although a crank seemed the obvious solution to the conversion Watt and Boulton were stymied by a patent for this, whose holder, James Pickard, and associates proposed to cross-license the external condenser. Watt adamantly opposed this and they circumvented the patent by their sun and planet gear in 1781.

Over the next six years, he made a number of other improvements and modifications to the steam engine. A double acting engine, in which the steam acted alternately on the two sides of the piston was one. He described methods for working the steam "expansively" (i.e., using steam at pressures well above atmospheric). A compound engine, which connected two or more engines was described. Two more patents were granted for these in 1781 and 1782. Numerous other improvements that made for easier manufacture and installation were continually implemented. One of these included the use of the steam indicator which produced an informative plot of the pressure in the cylinder against its volume, which he kept as a trade secret. Another important invention, one which Watt was most proud of, was the Parallel motion which was essential in double-acting engines as it produced the straight line motion required for the cylinder rod and pump, from the connected rocking beam, whose end moves in a circular arc. This was patented in 1784. A throttle valve to control the power of the engine, and a centrifugal governor, patented in 1788, to keep it from "running away" were very important. These improvements taken together produced an engine which was up to five times as efficient in its use of fuel as the Newcomen engine.

Because of the danger of exploding boilers, which were in a very primitive stage of development, and the ongoing issues with leaks, Watt restricted his use of high pressure steam – all of his engines used steam at near atmospheric pressure.

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