Report from the Select Committee on Steam Carriages/Trevithick2
Mercurii, 17o die Augusti, 1831.
Charles D.O. Jephson, Esquire,
in the chair.
Mr. Richard Trevithick, again called in; and Examined.
Are there any additional observations you wish to make to the Committee?—There are. I was asked what I had performed, and what was my opinion as to whether Steam power could be made useful on common roads in general, and the difference in effect between broad and narrow wheels on such roads, respecting their breaking up or settling down the surface, and what further advantages I might expect from my late improved Steam Engine. In answer, I beg to say, in 1804 I invented and introduced the high-pressure Steam and locomotive Engines, and also, in 1813, invented the Iron Tanks and Buoys for His Majesty's Navy. In 1814 I was engaged by the Spanish Government to construct in England nine high-pressure Steam Engines, and a mint, with pump-work, and everything complete for draining the great mines of Pasco, in Peru: they weighed 500 tons, in 20,000 pieces, the boilers each of six tons weight, all in single plates, and the cylinders each in six pieces, all carried up the mountains on mules' backs, and put together on the spot, by which the mines were effectually drained, the ores wound up, stamped, smelted, and coined; they remained in full work until the Spanish army retreated through the mines before the Patriots, and on their retreat broke the Engines, and threw them into the Engine pits. For a Report of my progress in Peru, see the first Number of the Geological Transactions of Cornwall, copied from the Lima Gazettes. In reply to the question put to me by the Committee of the House of Commons, respecting the probable progress of Steam power for locomotive purposes. I beg to say, on Railroads they have been proved to be useful to a certain extent, but are still defective, on account of their great weight of machinery and water, and the difficulty of getting water at all times, also a want of permanent safety against explosion; but, from a late improvement of mine, these obstacles are now removed, and when these late improvements are combined with my former locomotive Engines, they can be constructed so light as to travel at almost any speed, and thousands of miles, without a supply of water, and the risk of exploding is reduced to an impossibility, with a saving of considerably above fifty per cent, in fuel; all those improvements will appear in my statement hereafter. Travelling on common turnpike roads would be by far the greatest national advantage, but which, on the present plan, never can be accomplished, because the difficulties of getting a supply of water, and the inequalities of the surface of the roads, will always, under these circumstances, prevent the limited power to ascend the hills; and this objection is irremoveable, because, as the power at present increases, the weight increases in nearly the same ratio. At the present moment we have a proof of this, from the Engines travelling on common level roads being as nearly as possible in equilibrium, their power just capable of running their own weight at a fair speed, on a level surface; and they now only wait an increase of their power, independent of weight, to accomplish their general adaption to every purpose, both on the road and also to agriculture, and as the expence of fuel bears so small a proportion to horse labour, the removal of the present objections would accommodate their general use to unlimited advantages that the public are anxiously in search of. As the axles of Steam Carriages require to be straight, and the wheels perpendicular, there remains no objection to employing any width of wheel that the Road Inspectors require, which, to a certain extent, will reduce the resistance, instead of increasing it. It is my opinion, that all wheels now in use on common roads are much too narrow; but this ought to be accommodated to the materials that the road is formed with: for instance, narrow wheels on an iron road do not yield to the pressure of the weight, but keep themselves perfectly horizontal, and do not pulverize; but every Macadamized road, more or less, is subject to this inconvenience, and the narrower the wheels, the greater mischief is done to the road, and more resistance is given to the horses. The usual notion, that wheels grind the road, is wrong; if any difference, it is the roads grind the wheels, the road-material being generally the harder of the two; but the roads are injured by the wheels crushing the stone, by a narrow surface bearing on small points, or on single stones, the tenacity of which will not support the weight under narrow wheels; under wide ones, they would sustain no injury, because the wide wheel reduces its weight on each inch of surface in contact with the road, as the number of surface inches is increased by its additional width, and settles down the road firmly, and gives each stone a side support also, therefore by double the bearing on the road, half the weight is taken off from every bearing surface inch, and that in addition to the side support, by being bedded firmly, a wide wheel will. I have no doubt, save four out of five, if not nine out of ten stones that are crushed at present, and reduce the road expences in the same proportion; but while the fancy of having carriage-wheels out of upright with crooked axles is continued, wide wheels would be a serious objection; the inside and outside of the wheel being of different diameters, and going different speeds, must cause an increase of load to the horses, because their rubbing on the road and tendency to twist move the stones out of their bed in the road, and, instead of bedding them firmly, has the contrary effect; another great evil arises from the use of narrow wheels, they sink lower into the road, and the road being in part elastic, whatever that may be, is a resistance added to the horses according to its perpendicular rise and fall; the passing over sand or snow gives a proof of this on a larger scale, and wide surfaces will bed snow, and form a firm road, while narrow surfaces would defeat the effect. Another proof of wide surfaces bedding firmly, is seen in Cornwall, where the mills for stamping the ores in the mines have Steam Engines in constant work, lifting twelve inches high iron stampers of three or four hundred weight, of about seventy inches of bearing; at the bottom surface these form their own, bed, which is about a foot thick of Macadamized stones, and are an everlasting foundation, though the stamps pulverize at the surface as fine as sand. It would be advisable for the fore and hind wheels of Carriages to run about half the track out of a line from each other, because the bank that is formed by the fore wheel would be rebedded by the hind one, and the leveller the road is kept, the less the jolts, and of course the shoaler will be the ruts, while the surface of the road remains sound, and even the wear is scarcely any thing, and the crushing cannot take; place but in a very small degree; because the small gravel binding uniformly with the larger stones, supported on every side, brings the whole surface into uniform contact with the wheel, in which state but very little injury can be done; but when uneven or broken, the loose stones roll about without a support, and kept: so by narrow wheels, they independently receive the whole weight of the wheel, and instead of being bedded down are crushed to powder. The unnecessary, resistance given to Carriages and wear of roads by narrow wheels far exceeds all conception. As a proof that locomotive wheels will not injure the roads by slipping round. I give you the copy of a Report printed on the performance of the locomotive Engines on the Manchester Road for the premium. The following calculation, founded on the reported result, was made by Mr. Vignoles and Mr. Price, of Neath Abbey.—The maximum number of strokes was 142 per minute, while 440 yards were traversed in 43 seconds, diameters of wheels 50.1 inches, circumference 157.4 inches; 157.4×142 inches, equal to 621 yards, being, the velocity per minute of the circumference of the wheel, or 21 miles and 300 yards per hour; then as 60 seconds is to 621 yards, so is 43 seconds to 445 yards. Thus, the calculated distance of the run, considering the wheel as a perambulator, agrees within five yards with the space actually passed over, and this difference might arise from the most trifling in accuracy of noting the time, a quarter of a second at each end being sufficient to produce this discrepancy, so that it might fairly be concluded there was no slip ping of the wheels at a velocity of nearly 22 miles an hour with a load. If wheels will not slip round on iron roads, there can be no doubt but that they will be firm on common roads. A Steam Carriage never needs the wheel chained, or to be still in going down hill, because if a throttle cock is put between the dis charge pipe and the piston, it cannot go down hill any faster than the Steam is permitted to make its escape from before the piston, and if required would stand still instantly. Below is stated the commencement of both my high pressure and locomotive Steam Engines, with the advantages derived from them.— Since 1804, at which time I invented and erected this high pressure Engine, up to the present time, little improvement has been made in addition to my own. The first locomotive Engine ever seen was one that I set to work in 1804, on a rail-road at Merthyr Tydvil, in Wales, which performed its work to admiration, a correct copy of which is now in general use on the rail-roads; the advantages gained by this improvement was a detached Engine, independent of all fixtures, working with five times the power of Boulton and Watt's Engine, without condensing water, and the fire inclosed in the boiler surrounded with water, and a force draught created by the Steam for the purpose of working on the roads without a high chimney, and from this was copied all the boilers for Navigation Engines, which without it could not have been available; this being independent of brick-work, light, safe from fire, and occupying little room. In March 1830, Davies Gilbert. Esquire, then President of the Royal Society, wrote a Treatise on the improvement made in the efficiency of the largest Steam Engines in the world, then working in Cornwall, in which he states, that in 1798, he made trial of Boulton and Watt's Engines in that county, and found the average duty performed in the mines was 17,621,000lbs, lifted one foot high with one bushel of coals; and in 1830, when he published his Treatise on the improvements of the Steam Engines in the Cornish mines, he says, that the improvement was so great that a duty of 75,628,000l, lifted one foot high, with the same quantity of coals, was then performing in the mines; that when compared with the duty done in 1795, the improvement exceeded Boulton and Watt's Engines, as 3.865 to 1, or 27 to 7 nearly, and exceeded the standard of the old atmospheric Engines, that were at work in 1778, as 10.75 to 1, (at present some of the best Engines have performed a duty of 90 millions with a bushel of coals,) and the result of this great improvement has been, that not one Engine on Boulton and Watt's plan remains at work in Cornwall; and it is acknowledged by all the Cornish Miners that this improvement solely has been the salvation of their deep and extensive mines, without which the mines could not have continued to work; but from this increase of power and speed, a duty and saving both in fuel and size of four to one, which has caused the saving of coals in the Cornish mines alone to exceed one million sterling, and a constant saving of above one hundred thousand pounds per year. The saving of fuel in theory, by working with high steam, is 75 per cent, every time that the elasticity of the steam is doubled, because double the quantity of coals doubles the pressure, and increases the bulk three-eighths, and by working this steam expansively three-eighths more are gained, and not only theory but practice proves that gain on all the Cornish Engines; the usual height of steam is sixty pounds above the atmosphere, but if the boilers could be made safe against explosion and work with much higher steam, the advantages would almost exceed limit; the accidents that have taken place by explosion, do not appear to be, from overloading the safety valve, but from overheating the boiler, because low pressure boilers have often exploded, and this generally takes place immediately on setting the Engine to work; when the boiler is under water guage it must be red hot, and while the Engine is standing the water in the boiler is still, but the moment that the Engine starts, the sudden escape of steam from the boiler to the cylinder causes a great ebullition of the water, and splashes it over the red hot sides, which instantaneously generates a superabundant quantity of steam more than the strength of any boiler, however strong, can sustain, because one pound of melting iron will boil three pounds of water, therefore the red hot tubes of a boiler to be suddenly cooled by water splashing over them, would immediately generate a hundred times as much steam as the space of the boiler would contain, therefore while the feed is so uncertain and the height of water fluctuates so much in the boiler, no permanent safety can be relied on, however light the safety valve may be loaded, or strong the boiler may be; boilers fed with salt or even foul water are dangerous, they are often incrusted with salt, repeatedly heated red hot and quickly reduced in substance and strength. To prevent the salt accumulating, a constant stream of boiling water is ejected from, and cold water in its stead injected into the boiler, which occasions a constant fluctuation in the height of water in the boiler, and requires a constant caution in the Engineer to prevent mischief. A proof that boilers do not explode from the regular working pressure of steam, is by the portable gasholders of one sixteenth of an inch thick and ten inches diameter being regularly charged with thirty atmospheres, or 450 pounds to the inch without accident, and though this pressure is not one-half the pressure that the theory of the strength of iron would bear, yet boilers have often exploded, though the safety valves have never been loaded with one-eighth part of the pressure of the gasholders, or one sixteenth of the pressure of the theory of the strength of iron in proportion to the strength and diameter of boilers, when compared with the gasholders; therefore perfect safety can never be relied on under the present regulations. To remove these serious evils, save fuel; and give a considerable increase in the power of Engines with less space and weight. I have made an entire new Engine, both in principle and arrangements, the fire-place, boiler and condenser are formed of six wrought-iron tubes standing perpendicular on their ends, encircled the one within the other for the purpose of safety, and to occupy little room, also for keeping the boiler to one constant gauge, with fine distilled water, permanently working without loss, by condensing the steam and never suffering it to escape out of the Engine, but returning it from the condenser back again into the boiler every stroke of the Engine by a force pump, and where an Engine is perfectly tight it would work for ever without a re plenish of water; but to supply leaks a small evaporating apparatus is used for supplying the deficiency with distilled water, which effectually prevents any fluctuation in the height of water in the boiler or collecting sediment, and an impossibility of ever getting the boiler red hot, there being no space for the water to fly to out of the boiler but into the condenser; and this is so small, that if by any means the force pump did not return the water regularly from the condenser to the boiler, the space in the condenser, by taking one inch in depth of water out of the boiler, would fill-and glut the condenser so, that the Engine would stand still, and, as the water cannot diminish, it does not require a large quantity of water, or water space in the boiler, so necessary in other Engines, to guard against fluctuation in the feed, and prevent the boiler becoming red hot. The boiler being considerably less, the strength and room will be increased, and, never getting hot, the Engine might be worked with much higher steam; if so high as the gasholders are charged with, the theory gives a saving of fuel, weight and room over low-pressure Engines of sixteen to one, without a supply of water. I state this, to show the probable advantages that will arise from this new Engine. For my Engine to be one hundred horse power, to raise sufficient Steam, the fire tube must be three feet diameter, which would give the boiler a diameter of three feet eight inches, and that a half inch thick, according to the theory of the strength of iron, would sustain a pressure of 1,736 pounds to the inch, which is four times as great as the gasholders are charged with, and thirty-two times the pressure that the high-pressure Engines work with at present, which is still farther proof that the explosions have been solely occasioned by the boilers being under water gauge, and heated red hot. If after boilers have been forced on their trial by a cold-water pressure, to stand ten times the pressure that they are to be worked at, and a boiler should happen to explode, the shock would be first received by the next surrounding tube, and so on for six successive surrounding tubes; each space between the tubes would admit the Steam to escape gently up the chimney, without harm, and the outside tube that encircles the whole, might be made of three quarters of an inch thick, 80 that it would put injury from explosion beyond possibility. The arrangement of this new Engine embraces every advantage that can be wished for; safety, saving of fuel, lightness, little room, cheapness, simplicity, and nearly independent of water, it can be made applicable to any purpose, and much more effectual than horse power, the first cost of erection far less than a quarter the cost of horses; for the duty, performed, independent of the difference of expence between coals and horse feed, because a one-horse Engine will, by constant 'work; perform the work of four horses every twenty-four hours. For breaking up and tilling large commons very little establishment will be required. Another great national advantage will be gained, by the whole of the kingdom being abundantly supplied with fresh fish, as it will be in the power of every fishing-boat to get a small Engine, and bring fish to market all round the Coast while fresh, independent of wind,, this way be carried by locomotive Engines, in a few hours; to the interior of the country; besides, every merchant ship will be propelled by Steam, as an Engine of ten tons weight on the deck, occupying very little more room than a ton cask, would propel a ship of 500 tons five miles per hour with sixpence worth of coals, and will also pump the ship, weigh the anchor, and take in and out the cargo. The principles of the leading power being matured, all the applications will soon follow.