Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 3

CHAPTER III. SMEATON AND WATT.

In forming an estimate of Richard Trevithick, sen., as the forerunner, and of his son as following Watt, in the improvement of the steam-engine, it is necessary briefly to refer to the engines of Smeaton and of Watt in Cornwall.

The question of rebuilding the Eddystone Lighthouse led Smeaton to visit Plymouth in 1756, when he probably saw the Cornish mines; ten years afterwards he erected several large atmospheric engines, one of which was sent to Russia. In 1775 he supplied the Chacewater Mine, in Cornwall, with an atmospheric engine, having a 72-inch cylinder, 9-feet stroke, working nine strokes a minute. The main beam was of twenty pieces of fir timber, bolted together, and the cylinder was supported on twelve pieces of fir, in place of the beam of oak used by Trevithick, sen. The cylinder bottom was a half sphere, instead of the flat bottom as in Dolcoath. Three hay-stack boilers, each 15 feet in diameter, sup- plied steam of 1 lb. on the inch above the atmosphere, one of which was placed under the cylinder. The piston bottom was cased with wood to prevent loss of heat. The low steam pressure reduced its power of quick motion, and' its hollow cylinder bottom increased the consumption of fuel. It was to do the work of a 62-inch and a 64-inch cylinder that before had drained the mine. Smeaton says that, prior to 1769, one hundred engines had worked in the Newcastle-upon-Tyne collieries fifteen of them averaged a duty of 5.59 million lbs., raised one foot high by 84 lbs. of coal: such was the use and the economic power of the steam-engine prior to the Watt patent in 1769.

My method of lessening the consumption of steam, and consequently fuel, in fire-engines, consists in the following principles: First, that the vessel in which the powers of steam are to be employed to work the engine, which is called the cylinder in common fire-engines, and which I call the steam-vessel, must, during the whole time the engine is at work, be kept as hot as the steam which enters it; first, by enclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor other substance colder than the steam to enter or touch it during that time.

Secondly, in engines that are to be worked wholly or partially by condensation of steam, the steam is to lie condensed in vessels distinct from the steam-vessel or cylinder, though occasionally communicating with them. These vessels I call condensers; and whilst the engines are working, these condensers ought at least to be kept as cold as the air in the neighbourhood of the engines, by application of water or other cold bodies.

Thirdly, whatever air or other elastic vapour is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps, wrought by the engines themselves or otherwise.

Fourthly, I intend, in many cases, to employ the expansive force of steam to press on the pistons, or whatever may be used, instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may he wrought by the force of steam only, by discharging the steam into the open air after it has done its office.

Fifthly, where motions round an axis are required, I make the steam-vessels in form of hollow rings, on circular channels, with proper inlets and outlets for Le steam, mounted on horizontal axles like the wheels of a water-mill; within them are placed a number of valves that suffer any body to go round the channel in one direction only. In these steam-vessels are placed weights so fitted to them as entirely to fill up a part or portion of their channels, yet rendered capable of moving freely in them by means hereinafter mentioned or specified.

When the steam is admitted in these engines between these weights and the valves, it acts equally on both, so as to raise the weight to one side of the wheel, and by the reaction of the valves successively to give a circular motion to the wheel; the valves opening in the directions in which the weights are pressed, but not in the contrary.

As the steam-vessel moves round, it is supplied with steam from the boiler, and that which has performed its office may either be discharged by means of condensers or into the open air.

Sixthly, I intend in some cases to apply a degree of cold not capable of reducing the steam to water, but of contracting it considerably, so that the engines shall be worked by the alternate expansion and contraction of the steam.

Lastly, instead of using water to render the piston or other parts of the engines air or steam tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state.

In 1770 Watt sent his drawings to Soho for his first engine. The castings were made at Coalbrookdale, but were found exceedingly imperfect, and were thrown aside as useless.

In 1776 the first Watt engine was built at Soho, after much difficulty in finding suitable workmen, and many inquiries for the new engine were coining from Cornwall.

In 1777 Watt went to Cornwall and erected an engine at Wheal Busy, near Chacewater, and another at Ting Tang, near Redruth. Here he met the Hornblowers, who had been erecting engines in Cornwall for fifty years, they having come from Staffordshire.

Bonze seems to have been one of the early practical men. Watt says he found five of Bonze's engines in Cornwall with cylinders of from GO to 70 inches in diameter.

In 1778 Watt was again in Cornwall, and says, 'The engine at Chacewater goes satisfactorily, making fourteen strokes per minute'.

Watt's close top to the cylinder, and parallel motion, were great improvements over the open-top cylinder and segment-headed beam before in use but the condensing away from the cylinder, and use of an air-pump, were the leading features of his claims as an improver of the steam-engine. These changes led to a saving of fuel, and the improved mechanical form gave greater control, but neither the speed nor power of the engine was materially increased. The pressure of steam remained about the same. The vacuum was more perfect in the cylinder, but the labour of working the air-pump reduced the net gain, and the engine was still a low-pressure steam vacuum engine, though greatly improved in usefulness.

Watt says, in 1761 or 1762 I made some experiments on the force of steam in a Pepin's digester, and formed a species of steam-engine. But I soon relinquished the idea of constructing an engine upon this principle, from being sensible it would be liable to some of the objections against Savery's engine from the danger of bursting the boiler, and the difficulty of making the joints tight, and also that a great part of the power of the steam would be lost, because no vacuum was formed to assist the descent of the piston.

In 1782, Watt patents an expansive engine, applicable both to double and single engines. In both these forms of the apparatus the steam acts not only to form the vacuum, but to depress the piston. But still, during the operation of the counterpoise, it produces no effect and when it was required to move machinery, this suspension of impulse was a great drawback on its utility. This, however, was not objected to its general merit when used as a mover of pumps, and the more so, as it was common to the atmospheric engine.

The power of the condensing engine is easily known by ascertaining the temperature of the steam which moves the piston, the area of the piston, and the temperature of the vapour which remains in the condenser. It is, however, found most expedient to raise the steam to a somewhat higher temperature than 212°, so as to produce a pressure between 17 and 18 lbs. on each square inch of the piston; yet in practice, from the imperfect vacuum which is made in the condenser, and after making allowance for the friction of the piston on the sides of the cylinder, and for the friction of the various parts of the intermediate machinery, this pressure of 18 lbs. on each square inch of the piston cannot raise more water per inch than would weigh about 8.5lbs., so that somewhat more than a half of the whole power of the steam is absorbed to give motion to the intermediate mechanism.

In 1778 Smeaton applied to Watt for a licence to attach the patent condenser and air-pump to the atmospheric engine, and received the following reply:—

By adding condensers to engines that were not in good order, our engines would have been introduced into that county (which we look upon as our richest mine) in an unfavourable point of view, and without such profits as would have been satisfactory, either to us, or to the adventurers. Besides, where a new engine is to be erected, and to be equally well executed in point of workmanship and materials, an engine of the same power cannot be constructed materially cheaper on the old plan than on ours. The idea of condensing the steam by injecting into the eduction-pipe, was as early as the other kinds of condensers, and was tried at large by me at Kinneal. We shall have four of our engines at work in Cornwall this summer; two of them are cylinders of 63 inches diameter, and are capable of working with a load of 11 or 12 lbs. on the square inch.

Such was the estimate by those two eminent men of the relative power of the Watt and the Newcomen engine, using steam of a pressure just sufficient to overcome the weight of the atmosphere, trusting to the condensation and vacuum for its effective power. The vacuum was more perfect in the Watt engine than in the earlier atmospheric engine of Newcomen, but this seeming gain was much reduced by the power required to work the air-pump. A gross power, made up of 14 or 15 lbs. from vacuum, and 2 or 3 lbs, steam pressure, was reduced to one-half by the numerous drawbacks in the movements of the engine.

In 1712 the Griff atmospheric engine had an effective force of 10 lbs. on each square inch of the piston. In 1746 the atmospheric engine at Pool Mine, with steam of 2 or 3 lbs. to the inch above the atmosphere, worked fifteen strokes a minute. In 1758 Borlase said that the quickness of movement of the atmospheric engine in Cornwall depended on the steam pressure driving the engine faster or slower. In 1775 the Bullan Garden atmospheric worked sixteen strokes a minute. In 1778 Watt's Chacewater engine, with steam about 1 lb, on the inch above the pressure of the atmosphere, worked fourteen strokes a minute.

The working therefore of an engine by the elastic force of steam was more advanced a quarter of a century before Watt's patent, than a quarter of a century after it. The Newcomen pumping engine, when at rest, had its piston at the bottom of the cylinder, under which the valve admitted steam of 2 or 3 lbs. on the inch, counterbalancing the weight of the piston, and raising it to the top of the cylinder; a jet of cold water produced a vacuum, and caused the piston to descend with a force of 14 lbs. of atmospheric pressure on each square inch of its surface, together with its own weight of 2 or 3 lbs. on the inch.

The Watt pumping engine had a close-topped cylinder, with its piston at the top when at rest; a valve admitted on it steam of 1 or 2 lbs. on the inch; the equilibrium valve then allowed the steam to pass also into the portion of the cylinder under the piston an exhaust-valve at the bottom of the cylinder then passed the steam from under the piston to the condenser, where a jet of cold water caused a vacuum, and the piston descended with a force of 14 lbs. from vacuum, and 1 or 2 lbs. of steam pressure on the piston, being together no more than the atmospheric engine.

It is beyond our comprehension that for fifty years the use of the steam-engine was confined to the pumping of water. In 1780 Mr. Matthew Wasbrough and Mr. James Pickard gave rotary motion from the steam-engine by a crank. Watt objected to the use of his patent engine, if the crank was attached to it, and invented sun-and-planet wheels in place of the crank.

The rivalry of patent claimants, or ignorance, retarded the use of the rotary steam-engine until 1784. This is the more remarkable when bobs with connecting rods attached to cranks on the axles of water-wheels were in common use in Cornwall before 1758, and must have been seen by Watt during his residence there in 1777. They were so used by Trevithick, sen., before the time of Watt, in Bullan Garden and other mines in which Watt erected engines. There is this difference, that in the one case the crank gave motion to the bob, and in the other the bob gave motion to the crank.

More effectual is the water-wheel and bob: an engine whose power is answerable to the diameter of the wheels, and the length of the bobs, fastened to its axis by large iron cranks; a perpendicular rod of timber to each end of the bobs works a piston in a wooden or (which is far better) a brass hollow cylinder.

The drawing of Bullan Garden in Chapter II, shows the cranks, connecting rods, and beams, in general use in Cornwall for half a century before Watt used them.

In 1781, Wasbrough having entered into an arrangement with the Commissioners of the Navy to erect a crank engine for grinding flour at the Deptford Victualling Yard, made a formal application to Boulton and Watt to supply their engines for the pure pose: Watt protested that he could not bring himself to submit to such an indignity.

Up to 1780, the use of the steam-engine was confined to the raising of water. The earliest of Mr. Watt's steam-engines, giving a rotatory movement, were erected in 1784 — one for Mr. Whitbread's brewhouse, and one for the Albion Mills.

The crank was also about that time applied to atmospheric engines, but the disputes between Watt and others, on their priority of claim and patent rights, on the new invention of the old crank, retarded its use in the steam-engine for several years. Watt's first rotary engine, in 1784, had his sun-and-planet wheels, and the simple but unfortunate crank, with its patent Honours, had to wait still longer before it was allowed to take its place as the most useful limb in the growing steam-engine.

Cook's Kitchen water-wheel, still at work, though well known before the time of Watt, was thus spoken of in 1778:—

The water-engine at Cook's Kitchen Mine is 48 feet in diameter, and works her tiers of pumps of 9-inch bore, which, being divided into four lifts, draw 80 fathoms under the alit. The water-wheel with bobs, whose power is answerable to the diameter of the wheel, and the sweep of the cranks, fixed in the extremities of the axis; over them the large bobs are bung, upon brass centre gudgeons, supported by a strong frame of timber, and rise and fall according to the diameter of the sweep of the crank.

To each crank is fixed a straight half-split of balk timber, that communicates with each bob above at the other end or nose of the bob, over the shaft, a large iron chain is pendent, fastened to a perpendicular rod of timber, that works a piston in an iron or brass hollow cylinder."

This wheel, used by Trevithick, sen., a hundred years ago, was at work before Watt erected' 63-inch cylinder engine in Dolcoath, from which it was distant but a stone's throw. Hunter renewed it under Trevithick, jun., in 1803. In the Valley smiths' shop near it, Trevithick, jun., constructed his globular tubular boiler of 1800, and also his cylindrical boiler of 1811 for the Dolcoath engine.

Cook's Kitchen Water Wheel and valley Smiths' Shop

• Life of Richard Trevithick by F. Trevithick
• Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 2
• Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 4

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