The reader's attention has been very imperfectly drawn to the numeroussubjects touched on in these remnants of Trevithick's correspondencebetween the years 1804 and 1816; among them may be traced the portablehigh-pressure steam-engine, the tubular cylindrical boiler of wroughtiron, the economy of expansive working with steam of 100 lbs. on theinch, but limiting it to 20 lbs. when not in the charge of experiencedworkmen, and testing boilers by water pressure to four times theintended working pressure.
THE KING OF FIGHTERS XIV STEAM EDITION Free Download [portable Edition]l
"I received from Sir Charles Hawkins a copy of Dr. Logan's letter toyou, also a note from you to Sir Charles Hawkins, both respectingthe driving boats by steam; respecting the[Pg 41] engine for thrashing,chaff-cutting, sawing, &c. I am now making one of about two-thirdsthe size of Sir Charles Hawkins', which will be portable on wheels.By placing the engine in the farm-yard, and passing the rope from thefly-wheel through the barn-door, or window, and around the drum on themachine axle, it may be driven.
"Instead of a piston working in the main cylinder of the steam-engine,I do use a plunger-pole similar to those employed in pumps for liftingwater, and I do make the said plunger-pole nearly of the same diameteras the working cylinder, having[Pg 79] only space enough between the poleand the cylinder to prevent friction, or, in case the steam isadmitted near the stuffing box, I leave sufficient room for the steamto pass to the bottom of the cylinder, and I do make at the upperend of the cylinder for the plunger-pole to pass through a stuffingbox of much greater depth than usual, into which stuffing box I dointroduce enough of the usual packing to fill it one-third high. Uponthis packing I place a ring of metal, occupying about another thirdpart of the depth of the stuffing box, this ring having a circulargroove at the inside, and a hole or holes through it communicatingwith the outside, and with a hole through the side of the stuffingbox; or, instead of one ring containing a groove, I sometimes placetwo thinner rings, kept asunder by a number of pillars to about thedistance of one-third of the depth of the stuffing box, and I pack theremaining space above the ring or rings, and secure the whole downin the usual manner. The intention of this arrangement is to producethe effect of two stuffing boxes, allowing a space between the twostuffings for water to pass freely in from the boiler or forcing pumpthrough a pipe and through the hole in the side of the stuffing box,so as to surround the plunger-pole and form the ring of water for thepurpose of preventing the escape of steam by keeping up an equilibriumbetween the water above the lower stuffing and the steam in thecylinder. By this part of my said invention I obviate the necessity ofthat tight packing which is requisite when steam of a high pressureis used, and consequently I avoid a greater proportion of the usualfriction, because a very moderate degree of tightness in the packingis quite sufficient to prevent the passage of any injurious quantityof so dense a fluid as water. And I do further declare that I use theplunger-pole, working in a cylinder and through a double stuffing,either with or without a condenser, according to the nature of thework which the steam-engine is to perform."
"The great merit of establishing the practicability of so importantan application of steam, and the superiority of the high-pressureengine for this purpose, will perhaps more than any other circumstanceserve to do honour through all times to the name of Trevithick. Theexperiment which was made on the public road close by Camborne wasperfectly successful; and although many improvements in the detailsof such description of engines have been since effected, the leadingprinciples of construction and arrangements are continued, I believe,with little alteration, in the magnificent railroad-engines of thepresent day. Of his stamping engine for breaking down the black rock inthe Thames, his river-clearing or dredging machine, and his extensivedraining operations in Holland, I can only speak in general terms,that they were eminently successful, and displayed, it was considered,the highest constructive and engineering skill. As a man of enlargedviews and great inventive genius, abounding in practical ideas of thegreatest utility, and communicating them freely to others, he couldnot fail of imparting a valuable impulse to the age in which he lived;and it would be scarcely doing him justice to limit his claims as apublic benefactor to the inventions now clearly traceable to him,[Pg 111]important and numerous as these are. From my own impressions I may saythat no one could be in his presence without being struck with theoriginality and richness of his mind, and without deriving benefitfrom his suggestive conversation. His exploits and adventures in SouthAmerica, in connection with the Earl of Dundonald, then Lord Cochrane,will form an interesting episode in his career; and altogether, I am ofopinion that the Biography which you have undertaken will prove highlyinteresting and valuable, and I wish you every success in carrying itout.
At the period of those high-pressure pole-engine experiments,Trevithick had devoted twenty years of constant labour to theimprovement and extended use of the steam-engine, causing it toassume every variety of form except that of the Watt patent engine,an approach to which was unusual, as evidenced in the high-pressuresteam Kensington model of 1796, without beam, parallel motion,air-pump, or condenser, having no one portion either in principle ordetail similar to the Watt engine, being portable and not requiringcondensing water, with single and double cylinders,[Pg 113] placed verticallyor horizontally. Having during twelve busy years constructed over ahundred high-pressure steam-engines, scarcely any two of which wereexactly alike, he departed if possible still further from the Watttype, and went back apparently, though not in reality, to the Newcomenengine, simplifying it by the omission of the great bob, and use ofcondensing water, as in the nautical labourer and steamboat engineof about 1810,[43] and the South American mine engines of 1816,[44]which had open-top cylinders, more like a Newcomen than a Watt, butif possible even more simple and primitive-looking than the former.Again, compare the thrashing engine of 1812[45] with the Newcomen of1712:[46] the great and all-important difference being that one wasa high-pressure steam-engine, the other a low-pressure atmosphericengine. Then came the varieties of high-pressure steam pole-engines,working very expansively either as puffers or condensers, retaining thesame dissimilarity to the Watt engine: and lastly, the combination ofthe high-pressure pole with the Watt patent engine, thereby causing theold Watt engine to do more than double the work it had done when newfrom the hands of the maker, and also to perform this increase of workwith a decrease in the consumption of coal.
A great charm in Trevithick's character was his freedom and largenessof view in questions of competition. He was then making three enginesat Coalbrookdale, to be worked with high-pressure steam, combined withthe Watt air-pump and condenser; and though smarting from the contestwith his great rival, yet wrote, "I think it is better to make themourselves, for if we do not, some others will, for there must be asaving of coal by condensing. But with small engines,[Pg 137] or where coal isplentiful, the engine would be best without it."
The low price of tin and copper, which caused so many engines to ceaseworking about the close of the last century, had changed for thebetter, and the present century opened with an increasing demand forsteam power. Trevithick's high-pressure portable engines had workedsatisfactorily for several years; and as a means of making public therelative duty performed by Cornish pumping engines, and of solvingconflicting statements on the rival systems of low and high pressuresteam, it was determined that an intelligent person should examineand give printed monthly reports of the amount of duty done by thedifferent engines, and in 1810 Captain Andrew Vivian was requestedto take this work of engine reporter in hand; on his refusal it wasoffered to Trevithick. In August, 1811, Mr. Lean commenced such monthlyreports, showing that the duty of twelve pumping engines at the end ofthat year averaged seventeen millions, exactly the duty done by the[Pg 166]Boulton and Watt engines thirteen years before, as reported by DaviesGilbert and Captain Jenkin in 1798, proving the small inherent vitalityof the Watt engine.
Lean states that had the pumping engines at work in Cornwall in 1835remained unimproved since 1814, at which time they had benefited bythree years of continuous improvement, a yearly additional expenditureof 80,000l. for coal would have been the consequence, and that thefirst step was Trevithick's expansive steam from the cylindricaltubular boiler, engines using such steam performing a duty three orfour fold what Boulton and Watt had ever attained, or perhaps thoughtpossible of attainment.[118] The birth of the idea of using expansivesteam may in truth be traced back nearly one hundred years to the timeof Newcomen's atmospheric engine, and the hope expressed in 1746 ofa smaller boiler and more elastic steam[119] was partially realized inthe engine and boiler of Trevithick, sen., in Bullan Garden in 1775,followed in 1780 by the competing[Pg 192] engine erected by Watt in DolcoathMine, under Trevithick's management. Little further change was madeuntil 1799, when the globular boiler and internal tube of Trevithick,jun., gave a second start to the use in large engines of more expansivesteam; and even this partial move was the result of years of thoughtand practical experiment; for in 1792, when twenty-one years of age, hewas the elected judge on a competitive trial between the Watt engine atSeal-hole, patented in 1782, and Hornblower's double-cylinder engine atTin Croft. Each engine performed a duty of ten millions, both of themwere called expansive, while in fact neither of them were so, for thepressure of the steam in the boiler did not admit of it. As Lean says,"As the steam used was raised but little above the pressure of theatmosphere, it was found that the power gained did not compensate forthe inconvenience of a more complicated and more expensive machine."Or, as Watt said to Robert Hart, "We resolved to give up the expansionof the steam until we could get men that could work it," as he foundit more costly than profitable. Again in 1798, Trevithick's ownwriting records his experiment in Dolcoath between the Bullan Garden45-inch atmospheric engine and the Watt 63-inch great double-actingengine, when the latter did sixteen millions to ten millions by theatmospheric. At that very time he was constructing his high-pressuresteam portable engines, and in the following year, after seven years ofmost active experience, prompted by the Watt lawsuit against Cornishengineers, he in 1799 gave the beaten 45-inch engine steam of a higherpressure from the stronger globular boiler. People, following theideas of Watt, were still afraid of Trevithick's plans, distinctlylaid down in his letters of[Pg 193] 1806, recommending a cylindrical boilerfor the Dolcoath pumping engine, because similar boilers giving steamto his whim-engines have enabled them to beat the Watt whims. Thiscontinued until 1810, when the greatly-increased power and economyof the high-pressure expansive steam pumping engine at Wheal Prospercaused the neighbouring Dolcoath in 1811 to give Trevithick's plansfree scope. The long smouldering rivalry between low and high pressure,on the eve of the final discomfiture of the former, burst forth inloud words and evil prognostications, causing the mining interest ofCornwall to appoint an examiner who should publish monthly the dutyperformed by the various pumping engines, the first of which appearedin the autumn of 1811, when Trevithick was building his boilers inDolcoath, and preparing the engines, as far as was possible, to submitto strong steam. By expansive valves and suitable gear, balance ofpower between the engine and the pump-work necessitating balance-bobs,strengthening the pit-work to bear the more powerful and suddenmovement, and fifty other things, which we know must have presentedthemselves in such work, occupied the greater part of Trevithick's timefrom 1811 to 1814. That first report enumerates twelve pumping-engines,probably all of them Watt engines, averaging a duty of seventeenmillions. 2ff7e9595c