(194.)

(194.)In reviewing all that has been stated, it will be perceived that the efficiency of the locomotive engines used on this railway is mainly owing to three circumstances: 1st, The unlimited power of draft in the furnace, by projecting the waste steam into the chimney; 2d, The almost unlimited abstraction of heat from the air passing from the furnace, by arrangement of tubes traversing the boiler; and, 3d, Keeping the cylinders warm, by immersing them in the chamber under the chimney. There are many minor details which might be noticed with approbation, but these constitute the main features of the improvements.

The successive introduction of improvements in the engines, some of which we have mentioned, was accompanied by corresponding accessions to their practical power, and to the economy of fuel. In the spring of the year 1832, I made several experiments on the Manchester Railway, with a view to determine, in the actual state of the locomotive engines at that time, their powers with respect to the amount of load and the economy of fuel, from which I select the following as examples:—

I.On Saturday, the 5th of May, the engine called the "Victory" took 20 waggons of merchandise, weighing gross 92 tons 19 cwt. 1 qr., together with the tender containing fuel and water, of the weight of which I have no account, from Liverpool to Manchester (30 miles), in 1 h. 34 min. 45 sec. The train stopped to take in water half-way, for 10 minutes,[Pg358]not included in the above-mentioned time. On the inclined plane rising 1 in 96, and extending11⁄2mile, the engine was assisted by another engine called the "Samson," and the ascent was performed in 9 minutes. At starting, the fire-place was well filled with coke, and the coke supplied to the tender accurately weighed. On arriving at Manchester, the fire-place was again filled, and the coke remaining in the tender weighed. The consumption was found to amount to 929 pounds net weight, being at the rate of one third of a pound per ton per mile.Speed on the level was 18 miles an hour; on a fall of 4 feet in a mile,211⁄2miles an hour; fall of 6 feet in a mile,251⁄2miles an hour; on the rise over Chatmoss, 8 feet in a mile,175⁄8miles an hour; on level ground sheltered from the wind, 20 miles an hour. The wind was moderate, but direct ahead. The working wheels slipped three times on Chatmoss, and the train was retarded from 2 to 3 minutes.The engine, on this occasion, was not examined before or after the journey, but was presumed to be in good working order.II.On Tuesday, the 8th of May, the same engine performed the same journey, with 20 waggons, weighing gross 90 tons 7 cwt. 2 qrs., exclusive of the unascertained weight of the tender. The time of the journey was 1 h. 41 min. The consumption of coke 1040 lbs. net weight, estimated as before. Rate of speed:—Level175⁄8miles per hour.Fall of 4 feet in a mile22Fall of 6221⁄2Rise of 815On this occasion there was a high wind ahead on the quarter, and the connecting rod worked hot, owing to having been keyed too tight. On arriving at Manchester, I caused the cylinders to be opened, and found that the pistons were[Pg359]so loose, that the steam blew through the cylinders with great violence. By this cause, therefore, the machine was robbed of a part of its power during the journey; and this circumstance may explain the slight decrease in speed, and increase in the consumption of fuel, with a lighter load, in this journey, compared with that performed on the 5th of May.The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt. rest on the drawing wheels. The cylinders are 11 inches diameter, and 16 inches stroke, and the diameter of the drawing wheels is 5 feet.III.On the 29th of May, the engine called the "Samson" (weighing 10 tons 2 cwt., with 14-inch cylinders, and 16-inch stroke; wheels 4 feet 6 inches diameter, both pairs being worked by the engine; steam 50 lbs. pressure, 130 tubes) was attached to 50 waggons, laden with merchandise; net weight about 150 tons; gross weight, including waggons, 223 tons 6 cwt. The tender weighed 7 tons, making a gross load (including the engine) of 240 tons 8 cwt. The engine with this load travelled from Liverpool to Manchester (30 miles) in 2 hours and 40 min., exclusive of delays upon the road for watering, &c.; being at the rate of nearly 12 miles an hour. The speed varied according to the inclinations of the road. Upon a level, it was 12 miles an hour; upon a descent of 6 feet in a mile, it was 16 miles an hour; upon a rise of 8 feet in a mile, it was about 9 miles an hour. The weather was calm, the rails very wet; but the wheels did not slip, even in the slowest speed, except at starting, the rails being at that place soiled and greasy with the slime and dirt to which they are always exposed at the stations. The coke consumed in this journey, exclusive of what was raised in getting up the steam, was 1762 lbs., being at the rate of a quarter of a pound per ton per mile.

On Saturday, the 5th of May, the engine called the "Victory" took 20 waggons of merchandise, weighing gross 92 tons 19 cwt. 1 qr., together with the tender containing fuel and water, of the weight of which I have no account, from Liverpool to Manchester (30 miles), in 1 h. 34 min. 45 sec. The train stopped to take in water half-way, for 10 minutes,[Pg358]not included in the above-mentioned time. On the inclined plane rising 1 in 96, and extending11⁄2mile, the engine was assisted by another engine called the "Samson," and the ascent was performed in 9 minutes. At starting, the fire-place was well filled with coke, and the coke supplied to the tender accurately weighed. On arriving at Manchester, the fire-place was again filled, and the coke remaining in the tender weighed. The consumption was found to amount to 929 pounds net weight, being at the rate of one third of a pound per ton per mile.

Speed on the level was 18 miles an hour; on a fall of 4 feet in a mile,211⁄2miles an hour; fall of 6 feet in a mile,251⁄2miles an hour; on the rise over Chatmoss, 8 feet in a mile,175⁄8miles an hour; on level ground sheltered from the wind, 20 miles an hour. The wind was moderate, but direct ahead. The working wheels slipped three times on Chatmoss, and the train was retarded from 2 to 3 minutes.

The engine, on this occasion, was not examined before or after the journey, but was presumed to be in good working order.

II.

On Tuesday, the 8th of May, the same engine performed the same journey, with 20 waggons, weighing gross 90 tons 7 cwt. 2 qrs., exclusive of the unascertained weight of the tender. The time of the journey was 1 h. 41 min. The consumption of coke 1040 lbs. net weight, estimated as before. Rate of speed:—

On this occasion there was a high wind ahead on the quarter, and the connecting rod worked hot, owing to having been keyed too tight. On arriving at Manchester, I caused the cylinders to be opened, and found that the pistons were[Pg359]so loose, that the steam blew through the cylinders with great violence. By this cause, therefore, the machine was robbed of a part of its power during the journey; and this circumstance may explain the slight decrease in speed, and increase in the consumption of fuel, with a lighter load, in this journey, compared with that performed on the 5th of May.

The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt. rest on the drawing wheels. The cylinders are 11 inches diameter, and 16 inches stroke, and the diameter of the drawing wheels is 5 feet.

III.

On the 29th of May, the engine called the "Samson" (weighing 10 tons 2 cwt., with 14-inch cylinders, and 16-inch stroke; wheels 4 feet 6 inches diameter, both pairs being worked by the engine; steam 50 lbs. pressure, 130 tubes) was attached to 50 waggons, laden with merchandise; net weight about 150 tons; gross weight, including waggons, 223 tons 6 cwt. The tender weighed 7 tons, making a gross load (including the engine) of 240 tons 8 cwt. The engine with this load travelled from Liverpool to Manchester (30 miles) in 2 hours and 40 min., exclusive of delays upon the road for watering, &c.; being at the rate of nearly 12 miles an hour. The speed varied according to the inclinations of the road. Upon a level, it was 12 miles an hour; upon a descent of 6 feet in a mile, it was 16 miles an hour; upon a rise of 8 feet in a mile, it was about 9 miles an hour. The weather was calm, the rails very wet; but the wheels did not slip, even in the slowest speed, except at starting, the rails being at that place soiled and greasy with the slime and dirt to which they are always exposed at the stations. The coke consumed in this journey, exclusive of what was raised in getting up the steam, was 1762 lbs., being at the rate of a quarter of a pound per ton per mile.

(195.)The great original cost, and the heavy expense of keeping the engines used on the railway in repair, have pressed severely on the resources of the undertaking. One of the best[Pg360]constructed of the later engines costs originally 1500l.and sometimes more. The original cost, however, is far from being the principal source of expense: the wear and tear of these machines, and the occasional fracture of those parts on which the greatest strain has been laid, have greatly exceeded what the directors had anticipated. Although this source of expense must be in part attributed to the engines not having yet attained that state of perfection, in the proportion and adjustment of their parts, of which they are susceptible, and to which experience alone can lead, yet there are some obvious defects which demand attention.

The heads of the boilers are flat, and formed of iron, similar to the material of the boilers themselves. The tubes which traverse the boiler were, until recently, copper, and so inserted into the flat head or end as to be water-tight. When the boiler was heated, the tubes were found to expand in a greater degree than the other parts of the boiler; which frequently caused them either to be loosened at the extremities, so as to cause leakage, or to bend from want of room for expansion. The necessity of removing and refastening the tubes caused, therefore, a constant expense.

It will be recollected that the fire-place is situated at one end of the boiler, immediately below the mouths of the tubes: a powerful draft of air, passing through the fire, carries with it ashes and cinders, which are driven violently through the tubes, and especially the lower ones, situated near the fuel. These tubes are, by this means, subject to rapid wear, the cinders continually acting upon their interior surface. After a short time it becomes necessary to replace single tubes, according as they are found to be worn, by new ones; and it not unfrequently happens, when this is neglected, that tubes burst. After a certain length of time the engines require new tubing. This wear of the tubes might possibly be avoided by constructing the fire-place in a lower position, so as to be more removed from their mouths; or, still more effectually, by interposing a casing of metal, which might be filled with water, between the fire-place and those tubes which are the most exposed to the cinders and ashes. The unequal expansion of the tubes[Pg361]and boilers appears to be an incurable defect, if the present form of the engine be retained. If the fire-place and chimney could be placed at the same end of the boiler, so that the tubes might be recurved, the unequal expansion would then produce no injurious effect; but it would be difficult to clean the tubes, if they were exposed, as they are at present, to the cinders. The next source of expense arises from the wear of the boiler-heads, which are exposed to the action of the fire.

A considerable improvement was subsequently introduced into the method of tubing, by substituting brass for copper tubes. I am not aware that the cause of this improvement has been discovered; but it is certain, whatever be the cause, that brass tubes are subject to considerably slower wear than copper ones.

(196.)The expense of locomotive power having so far exceeded what was anticipated at the commencement of the undertaking, it was thought advisable, about the beginning of the year 1834, to institute an inquiry into the causes which produced the discrepancy between the estimated and actual expenses, with a view to the discovery of some practical means by which they could be reduced. The directors of the company, for this purpose, appointed a sub-committee of their own body, assisted by Mr. Booth, their treasurer, to inquire and report respecting the causes of the amount of this item of their expenditure, and to ascertain whether any and what measures could be devised for the attainment of greater economy. A very able and satisfactory report was made by this committee, or, to speak more correctly, by Mr. Booth.

It appears that, previous to the establishment of the railway, Messrs. Walker and Rastrick, engineers, were employed by the company to visit various places where steam power was applied on railways, for the purpose of forming an estimate of the probable comparative expense of working the railway by locomotive and by fixed power. These engineers recommended the adoption of locomotive power; and their estimate was, that the transport might be effected at the rate of ·278 of a penny, or very little more than a farthing per ton per mile. In the year[Pg362]1833, five years after this investigation took place, it was found that the actual cost was ·625 of a penny, or something more than a halfpenny, per ton per mile, being considerably above double the estimated rate. Mr. Booth very properly directed his inquiries to ascertain the cause of this discrepancy, by comparing the various circumstances assumed by Messrs. Walker and Rastrick, in making their estimate, with those under which the transport was actually effected. The first point of difference which he observed was thespeedof transport: the estimate was founded on an assumed speed of ten miles an hour, and it was stated that a four-fold speed would require an addition of 50 per cent. to the power, without taking into account wear and tear. Now, the actual speed of transport being double the speed assumed in the statement, Mr. Booth holds it to be necessary to add 25 per cent. on that score.

The next point of difference is in the amount of the loads: the estimate is founded upon the assumption, that every engine shall start with its full complement of load, and that with this it shall go the whole distance. "The facts, however, are," says Mr. Booth, "that, instead of afull loadof profitable carriagefromManchester, about half the waggonscome back empty; and, instead of the tonnage being conveyed the whole way, many thousand tons are conveyed only half the way; also, instead of the daily work being uniform, it is extremely fluctuating." It is further remarked, that in order to accomplish the transport of goods from the branches and from intermediate places, engines are despatched several times a-day, from both ends of the line,to clear the road; the object of this arrangement being rather to lay the foundation of a beneficial intercourse in future, than with a view to any immediate profit. Mr. Booth makes a rough estimate of the disadvantages arising from these circumstances, by stating them at 33 per cent. in addition to the original estimate.

The next point of difference is the fuel. In the original estimate,coalis assumed as the fuel, and it is taken at the price of five shillings and ten-pence per ton: now the act of parliament forbids the use of coal which would produce smoke; the company have, therefore, been obliged to usecoke, at[Pg363]seventeen shillings and sixpence a ton.[32]Taking coke, then, to be equivalent to coal, ton for ton, this would add ·162 to the original estimate.

These several discrepancies being allowed for, and a proportional amount being added to the original estimate, the amount would be raised to ·601 of a penny per ton per mile, which is within one fortieth of a penny of the actual cost. This difference is considered to be sufficiently accounted for by the wear and tear produced by the very rapid motion, more especially when it is considered that many of the engines were constructed before the engineer was aware of the great speed that would be required.

"What, then," says Mr. Booth, in the Report already alluded to, "is the result of these opposite and mutually counteracting circumstances? and what is the present position of the company in respect of their moving power? Simply, that they are still in a course of experiment, to ascertain practically the best construction, and the most durable materials, for engines required to transport greater weights, and at greater velocities, than had, till very recently, been considered possible; and which, a few years ago, it had not entered into the imagination of the most daring and sanguine inventor to conceive: and farther, that these experiments have necessarily been made, not with the calm deliberation and quiet pace which a salutary caution recommends,—making good each step in the progress of discovery before advancing another stage,—but amidst the bustle and responsibilities of a large and increasing traffic; the directors being altogether ignorant of the time each engine would last before it would be laid up as inefficient, but compelled to have engines, whether good or bad; being aware of various defects and imperfections, which it was impossible at the time to remedy, yet obliged to keep the machines in motion, under all the disadvantages of heavy repairs, constantly going on during the night, in order that the requisite number of engines might be ready for the morning's work. Neither is this great experiment yet complete; it is still going forward. But the most prominent difficulties have been in a great measure surmounted,[Pg364]and your committee conceive that they are warranted in expecting, that the expenditure in this department will, ere long, be materially reduced,—more especially when they consider the relative performances of the engines at thepresent time, compared with what it was two years ago."

In the half year ending 31st December, 1831, the six best engines performed as follows:—

In the half year ending 31st December, 1833, the six best engines performed as follows:—

(197.)Since the date to which the preceding observations refer, the locomotive engine has undergone several improvements in detail of considerable importance; among which, the addition of a third pair of wheels deserves to be particularly mentioned. An engine supported on three pair of wheels has great security in the event of the fracture of any one of the axles,—the remaining axles and wheels being sufficient for the support of the machine. Connected with this change is another, recommended by Mr. Robert Stephenson, by which the flanges are removed from the driving wheels, those upon the remaining pairs of wheels being sufficient to keep the engine in its position upon the rails. We shall now describe a locomotive engine similar in construction to those almost[Pg365]universally used at present on railroads, as well in this kingdom as in other countries.[33]

The external appearance of the engine and tender is shown in the engraving at the head of this chapter. Infig.97.is exhibited a vertical section of the engine made by a plane carried through its length; and infig.98.is exhibited a corresponding section of its tender,—the tender being supposed to be joined on to the engine at the part where the connecting points appear to be broken in the drawing. Infig.99.is exhibited the plan of the working machinery, including the cylinders, pistons, eccentrics, &c. which are under the boiler, by the operation of which the engine is driven.Fig.100.represents the tender, also taken in plan.

Infig.101.is represented an elevation of the hinder end of the engine next the fire-box; and infig.102.is represented a cross vertical section through the fire-box, and at right angles to the length of the engine, showing the interior of the boiler above and beside the fire-box, the rivets and bolts connecting the internal and external fire-boxes, the regulator, steam funnel, and steam dome.

Infig.103.is represented an elevation of the front of the engine next the smoke-box, showing the cylinder coversW, buffersT, &c.; and infig.104.is represented a section of the interior of the smoke-box, made by a vertical plane at right angles to the engine, showing the tube plate forming the foremost end of the boiler, the branchesSof the steam-pipe leading to the cylinders, the blast-pipep, the cylindersH, and the chimneyG.

The same letters of reference are placed at corresponding parts in the different figures.

The boiler, as has been explained in the engines already described, is a cylinder placed upon its side, the section of which is exhibited atA,fig.97.The fire-box consists of two casings of metal, one within the other. The fire-grate is represented atD. The tubes by which the products of combustion are[Pg366]drawn from the fire-box to the smoke-boxFare represented atE. Upon the smoke-box is erected the chimneyG. In the engine from which this drawing has been taken, and which was used on the London and Birmingham Railway, the boiler is a cylinder71⁄2feet long, and31⁄2feet in diameter. It is formed of wrought-iron plates5⁄16of an inch in thickness, overlapping each other, and bound together by iron rivets7⁄8of an inch in diameter and13⁄4inch apart. One of these rivets, as it joins two plates, is represented infig.95.The boiler is clothed with a boarding of wooda, an inch in thickness, and bound round by iron hoops screwed together at the bottom. Wood being a slow conductor of heat, this covering has the effect of keeping the boiler warm, and checking the condensation of steam which would otherwise be produced by the rapid motion of the engine through the cold air.

Fig. 95.

Fig. 96.

The external fire-box,B B, is a casing nearly square in its plan, being four feet wide outside, and three feet seven and a half inches long, measured in the direction of the boiler. It is constructed of wrought-iron plates, similar to those of the boiler. This box descends about two feet below the boiler, the top being semi-cylindrical, as seen infig.102., of a somewhat greater diameter than the boiler, and concentrical with it. The front of the fire-box next the end of the boiler has a circular opening equal in size to the end of the boiler. To the edge of this opening the boiler is fastened by angle irons, and rivets in the manner represented infig.96.These rivets are seen in section infig.97.

The internal fire-boxC,fig.97., is similar in shape to the external, only it is flat at the top, and close every where except at the bottom. Between it and the external fire-box an open space of three inches and a half is left all round, and on the side next the boiler this space is increased to four inches. This internal fire-box is made of copper plates,7⁄16[Pg367]of an inch in thickness, every where except next the boiler, where the thickness is7⁄8.

As the sides and front of the external fire-box, and all the surfaces bounding the internal fire-box, are flat, their form is unfavourable for the resistance of pressure. Adequate means are, therefore, provided for strengthening them. The plates forming the internal fire-box are bent outwards near the bottom, until they are brought into contact with those of the external fire-box, to which they are attached by copper rivets, as represented atfinfig.97.The plates forming the bounding surfaces of the two fire-boxes are fastened together by stays represented atkinfigs.97. and 102. These stays, which are of copper, have a screw cut upon them through their whole length, and holes are made through the plates of both fire-boxes tapped with corresponding threads. The copper screws are then passed through them, and rivets formed on their heads within and without, as seen infig.102.These screw rivets connect all parts of the plating of the two fire-boxes which are opposed to each other: they are placed at about four inches apart over the sides and back of the internal fire-place and that part of the front which is below the boiler.

Fig. 97.LONGITUDINAL VERTICAL SECTION OF A LOCOMOTIVE ENGINE.larger

Fig. 97.LONGITUDINAL VERTICAL SECTION OF A LOCOMOTIVE ENGINE.

larger

Fig. 98.LONGITUDINAL VERTICAL SECTION OF THE TENDER.

Fig. 99. PLAN OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.larger

Fig. 99. PLAN OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.

larger

Fig. 100.PLAN OF THE TENDER.

Fig. 101.ELEVATION OF THE HINDER END OF A LOCOMOTIVE ENGINE.

Fig. 102.CROSS VERTICAL SECTION OF THE ENGINE THROUGH THE FIRE-BOX.

Fig. 103.ELEVATION OF THE FOREMOST END OF THE ENGINE.

Fig. 104.CROSS VERTICAL SECTION OF ENGINE THROUGH THE SMOKE-BOX.

As the top of the internal fire-box cannot be strengthened by stays of this kind, ribs of wrought-iron, which are seen in their length atl, infig.97., and of which an end view is seen infig.102., are attached by bolts to it. These ribs are hollowed out, as seen infig.97., between bolt and bolt, in order to break their contact with the roof of the fire-box, and allow a more free passage to the heat through it. If they were in continuous contact with the fire-box, the metal composing them would become more highly heated, and would soon wear out, besides intercepting heat from the water. This part of the fire-box is subject to rapid wear, unless care be taken that the level of the water be preserved at its proper height in the boiler. Even when the boiler is properly filled, the depth of water above the roof of the fire-box is not considerable, and on the least neglect the roof may be exposed to the contact of steam, in which case it will soon be destroyed.

To prevent accidents arising from this cause, a leaden plug,[Pg368]represented atm,figs.97. and 102., is inserted in the roof of the internal fire-box. If the water be allowed to subside, this plug will melt out before the copper is very injuriously heated, and the steam rushing out at the aperture will cause the fire to be extinguished.

Copper fire-boxes are almost universally used; but sometimes, from the consideration of cheapness, the internal fire-box is constructed of iron.

In the plating which forms the back of the external fire-box, an oval aperture is formed, as represented in the back view of the engine,fig.101., for the fire-doorg. The plating of the internal fire-box around this aperture is bent at right angles to meet that of the external fire-box, to which it is fastened by a row of copper rivets. The fire-door is formed of two plates of wrought-iron, riveted together with a space of nine inches and a half between them. The air between these plates being an imperfect conductor of heat, keeps the outer plate of the fire-door at a moderate temperature.

In that part of the surface of the internal fire-box which forms the end of the boiler, holes are made to receive the extremities of the tubes, by which the air proceeding from the fire is drawn to the smoke-box at the remote end of the boiler. These tubes are represented in longitudinal section atE,fig.97., and their ends are seen in the surface of the internal fire-box infig.102., and in the remote end of the boiler where they terminate in the smoke-box infig.104.These tubes are formed of the best rolled brass, and their thickness in the engine, to which we now refer, is1⁄13of an inch. After the brass plating is bent into the form of a tube, and being overlapped, is properly soldered together, and the edges smoothed off, the tubes are made perfectly cylindrical by being drawn through a circular steel die.

Fig. 105.

The tube-plates (as those parts of the boiler ends in which the tubes are inserted are called) are bored with holes in corresponding positions, truly cylindrical, and corresponding in magnitude to the tubes, so that the tubes, when passed into them, will be just in contact with them. The length of the tubes is so regulated, that when extending from end to end of the boiler, and passing through the holes, they shall[Pg369]project at each end a little beyond the holes. The manner of fastening them so as to be water-tight is as follows:—A steel hoop or ferrule, made slightly conical, a section of which is exhibited atC.fig.105., the smaller end of which is a little less than the internal diameter of the tube, but which increases towards the outer end, is driven in as represented in the figure. It acts as a wedge, and forces the tube into close contact with the edges of the hole in the tube-plate.

When particular tubes in a boiler are worn out, and require to be replaced, their removal is easily effected. It is only necessary to cut the steel ferrule on the inside, and to bend it off from contact with the tube, by which means it can be loosened and withdrawn, and the tube removed.

In the engine to which this description refers there were one hundred and twenty-four tubes, the external diameter of which was15⁄8inch. The distance between tube and tube was3⁄4of an inch. The number of tubes vary in different engines, some having so many as one hundred and fifty, while the number in some is less than ninety. The evaporating power of an engine greatly depends on the proper number and magnitude of its tubes; and the experience which engineers have had on railways have led them gradually to increase the number of tubes, and diminish their magnitude. In the Rocket, already mentioned as having gained the prize on the opening of the Liverpool and Manchester Railway, the number of tubes was twenty-four, and their diameter three inches; but in all the engines subsequently made their number was augmented, and their diameter diminished. The practical inconvenience which limits the size of the tubes is their liability to become choked by cinders and ashes, which get wedged in them when they are too small, and thereby obstruct the draft, and diminish the evaporating power of the boiler. The tubes now in use, of about an inch and a[Pg370]half internal diameter, not only require to be cleared of the ashes and cinders, which get fastened in them after each journey, but it is necessary throughout a journey of any length that the tubes should be picked and cleaned by opening the fire door at convenient intervals.

The substitution of brass for copper tubes, which has been already mentioned as so great an improvement in the construction of locomotive engines, is ascribed to Mr. Dixon, who suggested them in 1833, being then the resident engineer of the Liverpool and Manchester Railway. They are said to last six or eight times as long as copper tubes of the same dimensions.

When tubes fail, they are usually destroyed by the pressure of the water crushing them inwards: the water enters through the rent made in the tube, and flowing upon the fire extinguishes it. When a single tube thus fails upon a journey, the engine, notwithstanding the accident, may generally be made to work to the end of its journey by plugging the ends of the broken tube with hard wood; the water in contact with which will prevent the fire from burning it away.

Tubes of the dimensions here referred to weigh about sixteen pounds, and lose from six to seven pounds before they are worn out. Their cost is about one pound each.

The tubes act as stays, connecting the ends of the boiler to strengthen them. Besides these, there are rods of wrought iron extended from end to end of the boiler above the roof of the internal fire-place. These rods are represented atoin their length infig.97., and an end view of them is seen infig.102.The smoke-boxF,fig.97.104., containing the cylinders, steam-pipe, and blast-pipe, is four feet wide, and two feet long. It is formed of wrought iron plates, half an inch thick on the side next the boiler, and a quarter of an inch elsewhere. The plates are riveted in the same manner as those of the fire-box already described. From the top of the smoke-box, which, like the fire-box, is semi-cylindrical, as seen in elevation infig.103., and in sectionfig.104., rises the chimneyG, fifteen inches diameter, and formed of1⁄8inch iron plates, riveted and bound round by hoops. It is flanged to the top of the[Pg371]smoke-box, as represented infig.104.Near the bottom of the smoke-box the working cylinders are placed, side by side, in a horizontal position, with the slide valves upwards. In the top of the external fire-box a circular aperture is formed fifteen inches in diameter, and upon this aperture is placed the steam-domeT(figs.97. 101, 102.) two feet high, and attached around the circular aperture by a flange and screw secured by nuts. This steam dome is made of brass3⁄8inch thick. In stationary boilers, where magnitude is not limited, it has been already explained, that the space allowed for steam is sufficiently large to secure the complete separation of the vapour from the spray which is mixed with it when it issues immediately from the water. In locomotive boilers sufficient space cannot be allowed for this, and the separation of the water from the steam is effected by the arrangement here represented. A funnel-shaped tubed′(figs.97. 102.), with its wide end upwards, rises into the steam-dome, and reaches nearly to the top of it. This funnel bends towards the back of the fire-box, and is attached by a flange and screws to the great steam-pipeS, which traverses the whole length of the boiler. The steam rising from the boiler fills the steam-domeT, and descends in the funnel-shaped tubed′. The space it has thus to traverse enables the steam to disengage itself almost completely from the priming. The wider part of the great steam-pipeais flanged and screwed at the hinder end to a corresponding aperture in the back plate of the fire-box. This opening is covered by a circular plate, secured by screws, having a stuffing-box in its centre, of the same kind as is used for the piston-rods of steam-cylinders. Through this stuffing-box the spindlea″of the regulator passes, and to its end is attached a winchh′, by which the spindlea″is capable of being turned. This winch is limited in its play to a quarter of a revolution. The other end of the spindlea″is attached to a platee′seen edgeways infig.97., and the face of which is seen infig.102.: this circular plateeis perforated with two apertures somewhat less than quadrants. That part of the plate, therefore, which remains not pierced forms two solid pieces somewhat greater than quadrants. This plate is ground so as to move in steam-tight[Pg372]contact with a fixed plate under it, which terminates at the wide end of the conical mouth of the steam-pipeS. This fixed circular plate is likewise pierced with two nearly quadrantal apertures, corresponding with those in the movable platee′. When the movable platee′is turned round by the winchh′, the apertures in it may be made to correspond with those of the fixed circular plate on which it moves, in which position the steam-pipeScommunicates with the funneld′by the two quadrantal apertures thus open. If, on the other hand, the winchh′be moved from this position through a quarter revolution, then the quadrantal openings in the movable plate will be brought over the solid parts of the fixed plate on which it moves, and these solid parts being a little more than quadrants, while the openings are a little less, all communication between the steam-pipeSand the funneld′will be stopped, for in this case the quadrantal openings in the fixed and movable plates respectively will be stopped by the solid parts of these plates. It will be evident that as the winchh′of the regulator is moved from the former position to the latter, in every intermediate position the aperture communicating between the funneld′and the steam-pipeSwill be less in magnitude than the complete quadrant. It will in fact be composed of two openings having the form ofsectorsof a circle less than a quadrant, and these sectors may be made of any magnitude, however small, until the opening is altogether closed.

By such means the admission of steam from the boiler to the steam-pipeSmay be regulated by the winchh′.

The steam being admitted to the steam-pipe passes through it to the front end of the boiler, and the pipe being enclosed within the boiler the temperature of the steam is maintained. The steam-pipe passing through the tube-plate at the front end of the boiler is carried to a small distance from the tube-plate in the same direction, where it is flanged on to a cross horizontal pipe proceeding to the right and to the left as represented infig.104.This cross pipe is itself flanged to two curved steam-pipesS(fig.104.), by which the steam is conducted to the valve-boxesV V. The lower ends of these curved arms are flanged on to the valve-boxes of the two cylinders[Pg373]at the ends nearest to the boiler. The opening of one of these is exhibited in the right hand cylinder infig.99.By these pipes the steam is conducted into the valve-boxes or steam-chests, from which it is admitted by slide-valves to the cylinders to work the pistons in the same manner as has been already described in the large stationary engines.

On the upper sides of the cylinders are formed the steam-chests or valve-boxes, which are exhibited atU(figs.97. 99. 104.). These are made of cast-iron half an inch thick, and are bolted to the upper side of each cylinder. At the front end they are also secured by bolts to the smoke-box, and at the hinder end are attached to the tube-plate. These valve-boxes communicate with the passagesmandnfig.99.leading to the top and bottom of the cylinder: these are called the steam-ports. They also communicate with a passageoleading to the mouth of a curved horizontal pipep′connecting the front ends of the two cylinders, as seen infigs.99. 104. These curved pipes unite in a single vertical pipep, called theblast-pipe, seen infigs.97. 104.: this vertical pipe becomes gradually small towards the top, and terminates a little above the base of the funnel or chimneyG. In the valve-box is placed the slide-valvevto which is attached the spindlel′. This spindle moves through a stuffing-boxk′, and is worked by gearing, which will be described hereafter. According to the position given to the slide, a communication may be opened between the steam-chest, or the waste-port, and either end of the cylinders. Thus when the slide is in the position represented infig.97.the steam-chest communicates with the front end of the cylinder, while the waste-port communicates with the hinder end. If, on the other hand, the spindlel′being pressed forward, move the slide to its extreme opposite position, the steam-portnwould communicate with the waste-porto, while the steam-chest would communicate with the steam-portm, steam would, therefore, be admitted to the hinder end of the cylinder, while the foremost end would communicate with the waste-port. It will be perceived that this arrangement is precisely similar to that of the slide-valves already described (133.). The slide-valve is represented on a larger scale infig.106., whereAis the hinder steam-port,[Pg374]Bthe foremost steam-port, andCthe waste-port. The surfacesD, separating the steam-ports from the waste-ports, are called the bars: they are planed perfectly smooth, so that the surfacesFandGof the slide-valve, also planed perfectly smooth, may move in steam-tight contact with them. These surfaces are kept in contact by the pressure of the steam in the steam-chest, by which the slide-valve is always pressed down. In its middle position, as represented by the dotted lines in the figure, both the steam-ports are stopped by the slide-valve, so that at that moment no steam is admitted to either end of the cylinder. On either side of this intermediate position the slide has an inch and a half play, which is sufficient to open successively the two steam-ports.

Fig. 106.

The cylinders are inserted at one end in the plate of the smoke-box, and at the other in the tube-plate of the boiler. They are closed at either end by cast iron covers, nearly an inch thick, flanged on by bolts and screws. In the cover of the cylinder attached to the tube-plate is a stuffing-box, in which the piston rod plays. The metallic pistons used in locomotive engines do not differ materially from those already described, and therefore need not be here particularly noticed. From their horizontal position they have a tendency to wear unequally in the cylinders, their weight pressing them on one side only; but from their small magnitude this effect is found to be imperceptible in practice. In the engine here described the stroke of the piston is eighteen inches, and this is the most usual length of stroke in locomotive engines. The piston, in its play, comes at either end within about half an inch of the inner surface of the covers of the cylinders, this space being allowed to prevent collision. In the foremost cover of the cylinder is inserted a cockq′(fig.97.99.), by which any water which may collect in the cylinder by condensation or priming may be discharged. A cockr′(fig.97.), communicating with a small tube proceeding from the branches of the waste pipep′(fig.104.), is likewise provided to discharge from that pipe any water which may be[Pg375]collected in it. After the steam has been admitted to work the piston through the slide-valve, and has been discharged through the waste-port by shifting that valve, it passes through the pipep′into the blast-pipep, from the mouth of which it issues, with great force, up the funnelG. When the motion of the engine is rapid, the steam from the two cylinders proceeds in an almost uninterrupted current from the blast-pipe, and causes a strong draft up the chimney. The heated air which passes from the mouths of the tubes into the smoke-box is drawn up by this current, and a corresponding draft is produced in the fire-box.

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