Report from the Select Committee on Steam Carriages/Trevithick
Veneris, 12° die Augusti, 1831.
Davies Gilbert, Esquire,
in the chair.
Mr. Richard Trevithick, called in; and Examined.
Have you been long conversant with Steam Engines?—Twenty-six years ago I invented a high pressure Steam Engine and a locomotive Engine, and since that time Boulton and Watt's Engines have been thrown aside in Cornwall, and the high pressure Steam Engines, with the improvements upon the boilers I have made, have been throwing Boulton and Watt's Engines constantly out of use, there is not one of those now in use in the mines. The average of the duty of Boulton and Watt's Engines, about twenty years ago, was taken by Mr. Gilbert, which gave, perhaps, about seventeen millions of pounds, lifted a foot high with a bushel of coals; and sometime after that, Mr. Gilbert made a Report in the Transactions of the Royal Society, that he had found one of my high pressure Engines in Cornwall was doing seventy-five millions; and in the same Report be stated, that they were doing nearly as seven to twenty-eight or four to one, and as ten to one on the Atmospheric Engines.
Have you lately paid attention to Steam Carriages on common roads?—I have noticed the Steam Carriages very much; I have been abroad for a good many years, and had nothing to do with them until lately, but I have it in contemplation to do a great deal on common roads; Railroads are useful for speed, and for the sake of safety, but not otherwise, every purpose would be answered by steam on common roads.
Is your machine applicable to Steam Carriages?—It is chiefly for that purpose, it works without water; now the Manchester Carriages use four tuns a day, two tuns that they take in when they start, and two that they take in midway of their journey; there is that weight to carry, and the loss of time.
You conceive Steam Carriages to be applicable to common purposes?—Yes, to every purpose a horse can effect.
Have you any plan particularly applicable to that purpose?—Yes. I have taken out a patent for that purpose; this, the Plan which I produce, [producing the same,] will show the principle. I built a twenty-horse engine in Cornwall, in order to try this: this I produce is for a Ship Engine. [Mr. Trevithick explained to the Committee the different parts of the Machine on the Plan.] The bursting of boilers has been occasioned by the boilers being left under guage neglected to be charged with water, and. I believe, by their getting foul and incrusting with salt from using salt-water; the low-pressure Engines have burst as well as the high pressure; if the tubes of the boilers are heated red-hot, and the Engine is standing at the time the water is still in, the boiler is quiet; but on the Engine setting to work, a discharge of Steam from the boiler to the cylinder causes a great ebullition in the boiler, and the water splashing over the hot sides makes a superabundant generation of steam. The space that would be filled instantaneously from the hot tubes being suddenly cooled, the space occupied by that superabundance would fill three hundred times the space usually allowed for steam, and a safety valve of five times the size would give no relief, or not in time; a proof that a high-pressure Steam Engine boiler has not been broken generally by the pressure of the high steam, but from being heated, is because the portable gasholders are about ten inches diameter, and the sixteenth of an inch thick, and they are charged with 30 atmospheres, or 450 lbs, each without accident; an accident never happens to them, and the pressure is not so great as on half of the strength of iron; the boilers of Steam Engines in Cornwall have hurst that have not been loaded to an eighth part of that pressure for the same substance and size of boilers; therefore that is a proof that they must have been broken by the heating of the boiler, and suddenly cooling it by a sudden expansion. The gasholders have never been heated and have never been injured; I have known instances where by turning cold water into a red-hot boiler they have exploded. An Engine I had the care of was injured by the neglect of one of the enginemen in that way. The boilers to the high-pressure Steam Engines on my construction are cylinders, one in the other, the inner cylinder containing fire, and the outer cylinder surrounds the water and leaves a space of about a foot between the two tubes for water. Where they have been neglected the fire-tube bas been made red-hot, and the splashing of the water over the hot tube from the ebullition occasioned by the escape of steam has burst the boiler by the water flowing over the red-hot sides, and generating steam faster than it can be discharged.
By neglected you mean that the tubes were not completely covered with water?—They are not covered with water. With my inferential Engine, that never can be the case.
Have the goodness to state to the Committee your opinion with respect to the wear of the road by Steam Carriages?—I think that the roads will not be injured so much by Steam Carriages in future as they have been, because there will be no need to chain the wheels; by putting the valve to the stop, the steam going off that has never yet been applied, there is no need to chain the wheel; that is very easily done; if the steam is prevented escaping; the piston must stand still, and it can be let down as gently as possible; they may either stop instantly or go as easily as they please; the throttle barrel will answer the purpose to throttle between the cylinder and the discharge pipe; that would be a saving of the roads.
Have you made any observation on the injury done to the road by a Carriage propelled not in the usual manner but by a motion communicated to its wheels?—I think the roads would be less injured by Steam Carriages than by horses, because the wheels will have very little more to carry now than they have with horses, and there are no horses' feet to injure the road, therefore that part of it is saved; the Engines now will be so very light that it will be scarcely felt; the power to draw the Carriage will be very little more than the weight of harness on the horses.
Would you be inclined, for the advantage of the road, to give greater width to wheels if you give greater velocity?—I would rather give greater width; I do not think the road is injured so much, there is less friction; if a two-inch wheel goes two inches deep, and a four-inch wheel goes only one inch deep, there is two to one difference in the friction, for the ascent in getting up out of a two-inch rut requires a great deal more friction; the wider the wheels in my opinion, though the greater extent the less the friction; they use wide wheels to go over soft ground on farms to prevent their sinking; there is a great friction, for it is always going down hill and the friction is pulling it up hill; there is a power thrown away, but that would not have been the case with a wider wheel.
Do you think for a greater weight with a great velocity of carriage, you could put wheels so wide that instead of doing injury they should do good to the road?—Yes; I think if the wheels had been as wide as they ought to have been to take the advantage of ease, they would rather have done a service to the road than an injury, that is to settle down the road; but the greatest folly I have ever seen is the wide waggon wheels which go free of turnpike duty, one part is nine feet round and the other part not above seven and a half or eight feet, one part is going faster than the other, and the one part must rub; had the wheel been upright and it was turned off, the point only would meet, but it would not be rubbing.
There is a particular width of wheel in which no injury will be done to the road, but rather good?—It will be rather good after the road has been mended to settle it down; there will be wear in it as at other times; but in certain states of the roads to settle them down they will be doing good, but at no state of the road could it do good with narrow wheels.
What would be the effect when the road was once settled?—You see very often roads which have been gravelled; in dry weather the dust blows away; they can never settle again, but if the broad wheels passed over to crush it over with the dust, it would settle down much firmer; but the narrow wheels slide so easy through that they sink down, and shove them on each side.
Is there any state of the road in which you think a wide wheel would do injury to the road?—No; there is no state of the road in which wide wheels will do an injury; if there was to be a wheel of an inch in diameter instead of six inches, it would be like a stamping wheel cutting the road constantly, but the width of the wheel takes off that; the tenacity of stone is equal to the weight.
Does not the whole of this refer to wheels that are cylindrical and the axles horizontal?—Yes, they ought to be straight; that is the very wheel which I want for a Steam Carriage with straight axles.
Is not the road injured in two ways by the wear of it, and by the separation of the materials?—The separation of the materials is not so likely to take place with wide wheels as with narrow.
That is the reason why narrow wheels injure the roads more than wide wheels?—Yes; and there is a much greater weight upon one pebble than is thrown on two or three, double the weight is thrown on one pebble than would otherwise be; then that pebble is crushed, for the stone does not bear strongly enough together to resist it.
For this reason, the operation of horses' shoes must be much more injurious than that of broad wheels?—Yes; they are more likely to break the hard stones than a dead weight. I think the horses' feet much more likely.
There are certain states of the roads in which the widths of the wheel would occasion your losing power, are there not?—No. I think not. I have heard that mentioned, but I think is not so.
Is there any slipping or sliding in the wheel of the Steam Carriage?—When the trial for the premium given on the Manchester Railway was decided, the Engines ran for a certain time, and the strokes were counted, and the distance was measured, and there were remarks made upon that day's performance, they found, by measuring the periphery of the wheel, the number of the strokes made, and the distance run, that there was not the least variation whatever; they could find no difference.
Was not that on a Railroad?—Yes.
The cylindrical wheel, with the horizontal axle, is the best for the road?—Yes.
Is there not much less likelihood to slip on a common road, than on an iron Railroad?—Yes.
Suppose there are sharp ascents upon a common road, how would that apply?—There is no ascent that any common carriages go over, where the Steam Carriage will not go down hill with one wheel chained; no road in the neighbourhood of London that they would not run down with one wheel chained; that is, only one quarter part of the weight of the Carriage, if the wheel is chained, if you are drawing up hill with two or four wheels driven by an Engine, by their all turning round, they are as likely to go up hill. One wheel ought to put it up hill. It will go up a hill of double that ascent without slipping.
Will the increasing breadth of the wheel render slipping in ascending a hill more or less likely to take place?—I rather think that will increase the friction, because that does not tend to make a rut. In making a rut there is a very great difficulty in the wheel getting out of that rut, for there is no footing; but where it does not sink, that is not the case.
Supposing the width of the wheel to be the same on a Carriage and Steam Engine, and the weight of the Carriage the same, do you consider that a wheel perfectly cylindrical, with a horizontal axle, preferable to a wheel dished like that of a common stage coach, with a common axle?—You cannot have a dished wheel to a great width, without its dragging as I have described, unless you alter the system. If you keep the present dish, you must have a narrow wheel, or it is rubbing; but if it is a straight axle, it ought to be as wide as that where there is no more friction, and then the wide wheel will not do half the mischief that the coach-wheel does. The present stage coach-wheel will do a great deal more mischief, working as it does, than if it had been perpendicular.
Are you to be understood that in no state of the road a wide wheel such as you have described would do injury to the road?—A wide wheel will do a partial injury, but not one quarter of that which it would do if it were narrow.
What sort of injury will it do?—It will tend to crush the pebbles and wear them, but that will be very trifling indeed; if you have a hundred weight upon a wheel of an inch wide, and a hundred weight upon a wheel of two inches wide, that one of an inch wide will break ten times as many pebbles as the other; every inch it goes will break stones; a wide wheel does away the injury.
You are aware that in the carriages that run at present on the common roads the wheels do not run in the same track, in the event of having wheels with the tires four inches wide, do you think it would be better that the tire of the hind wheels should run in the same track or a different track?—For the Carriage making one turn only, it is easier for the wheels to go on the same track; but if you wish to take the average of the duty, they never ought to go in one track.
You think in the Steam Carriages that the tire of the hind wheels should go in different tracks?—Yes; the one produces a burr, and the other smooths it down.
Will the Carriage run so easy?—No; it would for one turn; but in the course of time, going every day backwards and forwards, the work will be done easier.
You think the tire may be extended to almost any width; what is the width which you think a Steam Engine travelling rapidly ought to have?—It depends upon the weight they have to carry; but if you draw a conclusion from the Coaches carrying four tons on two-inch wheels, you might, with a great deal of convenience to the Engine, make them six; but a six-inch wheel would not break one-tenth part of the stones which a two-inch would.
You see no objection to a Steam Carriage, intended to travel fast with passengers, which may weigh as much as a coach and four with its horses, having a six-inch tire?—No; I know it is condemned by people in general; but I have never beard, nor have I seen, any reason for its being condemned.
The wheels being wide and being cylindrical, with their axle horizontal, supposing you were to double the diameter, or to increase the diameter considerably of a wheel six inches wide, would it go more easily for the road?—It would go easier for the machine; but then there must be a wheel of double the width, and that would be loading the machine in going up hill with an unnecessary weight; but that would ease the road; it will have a longer bearing on the ground; there would not be so quick a circle.
With respect to the road, there would be a considerable advantage?—Yes, for it is a larger arch.
With respect to the Engine, would there be any other disadvantage but the additional weight?—No; I do not know any material objection except that, and that would throw the Engine very high; it would be top heavy. I do not think it would be convenient to make wheels above six feet.
Can you state the weight of your Engine as compared with the weight of the present Engine?—I will furnish an answer to that question.
Do you conceive that your Engine, of which you have produced a plan, is as applicable to Carriages on roads as to the propelling Engines at sea?—Yes, that is one object I have in view, and for agricultural purposes, for ploughing, and every other purpose.
Have you ever calculated what the weight of a Carriage would be with one of your Engines?—Yes; I am looking to see the necessity of the doing away with the supply of water that I have done away with; but in dispensing with the water I shall save three-quarters of the fuel; every time we double the force of Steam we save seventy-five per cent, upon it. This Engine, I conceive, will not take one quarter part of the fuel; one charge of water will do for a month. I have just taken out a patent for my Engine.
Do you condense with a sufficient rapidity to take from the piston the pressure of the returning steam?—Yes; there was an Engine which had been working with high steam and one of my boilers, and the cylinder was inclosed with brick-work, to keep off the external air; while I was abroad they took down the brick-work, and set it at a distance from the cylinder of four or five inches, and turned the draught from the fire round the cylinder to keep it off, and from that made more than sixty per cent, difference in the fuel; if the Engine was doing forty millions to a bushel of coals before, it then did sixty-three millions, and they burnt five bushels of coals to keep the cylinder hot; if they had put that under the boiler, it would have done forty millions, as before; but in putting in five bushels round the boiler, it did three hundred and fifty-six millions; then the difficulty was to know how it would make that difference; I could not at first make it out; however it turned out afterwards how it was, and it was the steam; when coming in upon the piston, the cold sides of the cylinder took out a part of the heat; these are single Engines; the steam is returned under the piston upon the Engine going that stroke again; the cold sides of the cylinder caused a dew by the steam; the steam was expanded to full four times the space; by the time it had gone a quarter part it was shut; then it was expanded; it was entirely cooled by itself; but when it came to touch the cold sides of the cylinder, it hung about them like a dew; the moment there was a communication to the condenser, that instant it expanded, and it threw itself into a second (illegible text); the next stroke threw that heat again into the side of the cylinder, the weight of the cylinder was about six tons; if it had taken out one degree each time, that would have taken out more than the Engine burnt. There is a clear proof how quick cold (illegible text) will condense.
Are there not Steam Engines in which the cylinder is within the boiler?—Yes; those are commonly used now in the high-pressure Steam Engines.
Have you ever considered what toll should be charged upon Steam Carriages, assuming that a Steam Carriage of 40 cwt, is equal to four horses, and does no more damage than four horses would do upon a road?—I should judge that there would be no need to fix them heavier than just to pay for repairing the road, whatever it may be; people are not to get their maintenance out of roads; and if the Steam Carriages do not injure the roads half as much as a common carriage, they should not pay half so much.
You do not suppose that a Steam Carriage weighing four tons would do more injury than a horse carriage?—A Steam Carriage with the same weight would do nothing like the same injury as a horse coach, for they have narrow wheels and these have not; and there are no horses' feet.
Your opinion is that there should not be a higher toll charged upon those Steam Carriages than upon a coach drawn by four horses?—If the toll is charged according to the injury done to the road, it would be not more than half.
Do you conceive there would be any difficulty in applying Steam Carriages to the present roads with the present ascents?—Under the present circumstances there is a difficulty; it is a question whether it shall go over the road, for the weight is too great; but if the weight is done away, and three to one in power added, it will be possible to do it, and I have 110 doubt it will be effected on my principle.
You think that the Steam Engines already prepared the home would go on the common roads?—They are between sinking and swimming at present, and I think they will swim; I think that the improvement is effected, and that they will do.
Would it not lighten the weight of Engines if you had fixed stationary Engines to pump gas, fifty atmospheres for instance; and shift the vessel containing it at each stage?—We do not want air or gas.
Something that has a power to drive?—A vessel that weighed that would be so heavy, it would not carry its own weight; the vessel it was compressed into would be of very considerable weight; a cubic inch of water will fill a cubic foot.
In the application of your power to a Steam Carriage, do you suppose there would be less danger of bursting than at present exists?—Yes; this cannot burst; that is prevented.
Have the goodness to state your reason?—There are five separate cylinders, the one encircled in the other; and if the boiler, or the inner circle burst, there are four other circles that might take the pressure, one after the other, before it can externally explode, which outer circles are never heated; and the boiler can never be heated or low, because the steam that is made use of by the Engines is returned every stroke into the boiler, and provided an Engine is tight, may work for ever without a fresh supply of water.
What height would the shaft be, as applied to your Steam Carriage?—It does not require to be higher than a common Steam Carriage.
Have the Steam Carriages that now ply on the roads a shaft?—No; they get their fuel through a fire door, but it will answer best to fill through you get considerable advantage. In the first place, you have a less boiler; by having a less boiler it is lighter; it is much stronger by getting a greater pressure; there is 75 per cent, of the fuel; if you take the average of the advantages, it will save daily nearly ten to one on travelling Engines.
That will render it necessary to have a chimney in a Steam Carriage?—A chimney is not necessary for the sake of draught if there is a forced draught; the Engine, of which I have produced a drawing, is made for a ship, where we are not bound to height, but five or six feet would be quite sufficient.
Do you apprehend that in your Engine there would be any noise from friction, so as to alarm horses?—No more than in any other Engines; there is no more noise, whether the steam is generated in the same way or how it is conducted, makes no difference.
With what would you work?—With coke; that would be the most convenient.
Do you think the road would suffer less damage from the Carriage itself containing the Engine conveying the passengers, or conducting another Carriage intended to convey passengers?—I think it better to have separate Carriages for the roads, as well because there is less weight upon the wheels; the weight would be more equally divided on the four wheels; but there will be six wheels in a general way I think. The two fore wheels will bear but very little weight.
Might not a single truck wheel do for that?—It would not be steady.