Sunday, November 1, 2015

A History of the Growth of the Steam Engine

A History of the Growth of the Steam Engine

Thomas SaveryThomas Savery was a member of a well known family of Devonshire, England, and was born at Shilston, about 1650. He was well educated, and became a military engineer. He exhibited great fondness for mechanics, and for mathematicians natural philosophy and gave much time to experimenting, to the contriving of various kinds of apparatus, and to invention. He constructed a clock, which still remains in the family, and is considered an ingenious piece of mechanism, and is said to be of excellent workmanship.
He invented and patented an arrangement of paddlewheels, driven by a capstan for propelling vessels in calm weather, and spent some time endeavoring to secure its adoption by the British Admiralty and the Wavy Board, but met with no success. The principal objector was the Surveyor of the Navy, who dismissed Savery, with a remark which illustrates a spirit which, although not yet extinct, is less frequently met with in the public service now than then:
"And have interloping people, that have no concern with us, to do to pretend to contrive or invent things for us?"
Savery then fitted his apparatus into a small vessel, and exhibited its operation on the Thames. The invention was never introduced into the navy, however.
It was after this time that Savery became the inventor of a steam engine. It is not known whether he was familiar with the work of Worcester, and of earlier inventors. Desaguliersu states that he had read the book of Worcester, and that he subsequently endeavored to destroy all evidence of the anticipation of his own invention by the marquis by buying up all copies of the century that he could find, and burning them. The story is scarcely credible. A comparison of the drawings given of the two engines exhibits, nevertheless, a striking resemblance; and, assuming that of the marquis's engine to be correct, Savery is to be given credit for the finally successful introduction of the "semi-omnipotent " and " water-commanding " engine of Worcester.
The most important advance in actual construction, therefore, was made by Thomas Savery. The constant and embarrassing expense, and the engineering difficulties presented by the necessity of keeping the British mines, and particularly the deep pits of Cornwall, free from water, and the failure of every attempt previously made to provide effective and economical pumping machinery, were noted by Savery, who, July 2, 1698, patented the design of the first engine which was ever actually employed in this work. A working model was submitted to the Royal Society of London.
Done in 1699, and successful experiments were made with it Savery spent a considerable time in planning his engine and in perfecting it, and states that he expended large sums of money upon it. Having finally succeeded in satisfying himself with its operation, he exhibited a model "Fire Engine," as it was called in those days, before King William III. and his court, at Hampton Court, in 1698, and obtained his patent without delay. The title of the patent reads:
"A grant to Thomas Savery of the sole exercise of a new invention by him invented, for raising of water, and occasioning motion to all sorts of mill works, by the important force of fire, which will be of great use for draining mines, serving towns with water, and for the working of all sorts of mills, when they have not the benefit of water nor constant winds; to hold for 14 years; with usual clauses."
Savery now went about the work of introducing his invention in a way which is in marked contrast with that usually adopted by the inventors of that time. He commenced a systematic and successful system of advertisement, and lost no opportunity of making his plans not merely known, but well understood, even in matters of detail. The Royal Society was then fully organized, and at one of its meetings he obtained permission to appear with his model " fire engine " and to explain its operation; and, as the minutes read;
"Mr. Savery entertained the Society with showing his engine to raise water by the force of fire. He was thanked for showing the experiment, which succeeded, according to expectation, and was approved of." 
Savery's Steam Engine 1702
What with the intention of making his invention more generally known, and hoping to introduce it as a pumping engine in the mining districts of Cornwall, Savery wrote a prospectus for general circulation, which contains the earliest account of the later and more effective form of engine. He entitled his pamphlet " The Miner's Friend; or, A Description of an Engine to raise Water by Fire described, and the manner of fixing it in 3 lines, with an account of the several uses it is applicable to, and an Answer to the Objections against it." It was printed in London in 1702, for S. Crouch, and was distributed among the proprietors and managers of mines, who were then finding the flow of water at depths so great as, in some cases, to bar further progress. In many cases, the cost of drainage left no satisfactory margin of profit. In one mine, 500 horses were employed raising water, by the then usual method of using horse gins and buckets.
It was also used for supplying water to towns; some large estates, country houses, and other private establishments, employed them for the same purpose. They did not, however, come into general use among the mines, because, according to Desaguliers, they were apprehensive of danger from the explosion of the boilers or receivers. As Desaguliers wrote subsequently:
" Savery made a great many experiments to bring this machine to perfection, and did erect several which raised water very well for gentlemen's seats, but could not succeed for mines, or supplying towns, where the water was to be raised very high and in great quantities; for then the steam required being boiled up to such a strength as to be ready to tear all the vessels to pieces." "I have known (Captain Savery, at York's buildings, to make steam eight or ten times stronger than common air; and then its heat was so great that it would melt common soft solder, and its strength so great as to blow open several joints of the machine; so that he was forced to be at the pains and charge to have all his joints soldered with hard solder."
Although there were other difficulties in the application of the Savery engine to many kinds of work, this was the most serious one, and explosions did occur with fatal results. The writer just quoted relates, in his " Experimental Philosophy;
" that a man who was ignorant of the nature of the engine undertook to work a machine which Desaguliers had provided with a safety valve to avoid this very danger, " and, having hung the weight at the further end of the steelyard, in order to collect more steam in order to make his work the quicker, he hung also a very heavy plumber's iron upon the end of the steelyard; the consequence proved fatal; for, after some time, the steam, not being able, with the safety cock, to raise up the steelyard loaded with all this unusual weight, burst the boiler with a great explosion, and killed the poor man."
This is probably the earliest record of a steam boiler explosion.
Savery proposed to use his engine for driving mills; but there is no evidence that he actually made such an application of the machine, although it was afterward so applied by others. The engine was not well adapted to the drainage of surface land, as the elevation of large quantities of water through small heights required great capacity of receivers, or compelled the use of several engines for each case. The filling of the receivers, in such cases, also compelled the heating of large areas of cold and wet metallic surfaces by the steam at each operation, and thus made the work comparatively wasteful of fuel. Where used in mines, they were necessarily placed within 30 feet or less of the lowest level, and were therefore exposed to danger of submergence whenever, by any accident, the water should rise above that level. In many cases this would result in the loss of the engine, and the mine would remain "drowned," unless another engine should be procured to pump it out. Where the mine was deep, the water was forced by the pressure of steam from the level of the engine station to the top of the lift. This compelled the use of pressures of several atmospheres in many cases; and a pressure of three atmospheres, or about 40 pounds per square inch, was considered, in those days, as about the maximum pressure allowable. This difficulty was met by setting a separate engine at every 60 or 80 feet, and pumping the water from one to the other. If any one engine in the set became disabled, the pumping was interrupted until that one machine could be repaired. The size of Savery's largest boilers was not great, their maximum diameter not exceeding two and a half feet. This made it necessary to provide several of his engines, usually, for a single mine, and at each level. The first cost and the expense of repairs were exceedingly serious items. The expense and danger, either real or apparent, were thus sufficient to deter many from their use, and the old method of raising water by horse power was adhered to.
The consumption of fuel with these engines was very great. The steam was not generated economically, as the boilers used were of such simple forms as only could then be produced, and presented too little heating surface to secure a very complete transfer of heat from the gases of combustion to the water within the boiler This waste in the generation of steam in these uneconomical boilers was followed by still more serious waste in its application, without expansion, to the expulsion of water from a metallic receiver, the cold and wet sides of which absorbed heat with the greatest avidity The great mass of the liquid w as not, however, heated by the steam, and was expelled at the temperature at which it was raised from below Savery quaintly relates the action of his machine in " The Miner's Friend," and so exactly, that a better description could scarcely be asked;
" The steam acts upon the surface of the water in the receiver, which surface only being heated by the steam, it does not condense, but the steam gravitates or presses with an elastic quality like air, and still increasing its elasticity or spring, until it counterpoises, or rather exceeds, the weight of the column of water in the force pipe, which then it will necessarily drive up that pipe; the steam then takes some time to recover its power, but it will at last discharge the water out at the top of the pipe You may see on the outside of the receiver how the water goes out, as well as if it were transparent; for, so far as the steam is contained within the vessel, it is dry without, and so hot as scarcely to endure the least touch of the hand; but so far as the water is inside the vessel, it will be cold and wet on the outside, where any water has fallen on it; which cold and moisture vanish as fast as the steam takes the place of the water in its descent."

After Savery's death, in 1716, several of these engines were erected in which some improvements were introduced.

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