Chapter I (15)

The draught of the furnace is produced in the same manner as in the Rocket, by ejecting the waste steam coming from [Pg348] the cylinder into the chimney; the boiler, however, differs considerably from that of the Rocket. A recurved tube passes through the boiler, somewhat similar to that already described in the early engine of Messrs. Trevethick and Vivian. In the horizontal section (_fig._ 91.), D expresses the opening of the furnace at the end of the boiler, beside the chimney. The grate-bars appear at A, supporting the burning fuel; and a curved tube passing through the boiler, and terminating in the chimney, is expressed at B, the direction [Pg349] of the draught being indicated by the arrow; C is a section of the chimney. The cylinders are placed, as in the Rocket, on each side of the boiler; each working a separate wheel, but acting on spokes placed at right angles to each other. The tube in which the grate and flue are placed diminishes in diameter as it approaches the chimney. At the mouth where the grate was placed, its diameter was two feet; and it was gradually reduced, so that, at the chimney, its diameter was only fifteen inches. The grate-bars extended five feet into the tube. The surface of water exposed to the radiant heat of the fire was sixteen square feet; and that exposed to the action of the heated air and flame was about seventy-five square feet. The magnitude of the grate, or sheet of burning fuel which radiated heat, was ten square feet.

(190.) The Novelty, of Messrs. Braithwaite and Ericson, is represented in _fig._ 92.; and a section of the generator and boiler is exhibited in _fig._ 93.; the corresponding parts in the two figures are marked by the same letters.

A is the generator or receiver containing the steam which works the engine; this communicates with a lower generator B, which extends in a horizontal direction the entire length of the carriage. Within the generator A is contained the furnace F, which communicates in a tube C, carried up through the generator, and terminated at the top by sliding shutters, which exclude the air, and which are only opened to supply fuel to the grate F. Below the grate the furnace is not open, as usual, to the atmosphere, but communicates, [Pg350] by a tube E, with a bellows D; which is worked by the engine, and which forces a constant stream of air, by the tube E, through the fuel on F, so as to keep that fuel in vivid combustion. The heated air contained in the furnace F is driven on, by the same force, through a small curved tube marked _e_, which circulates like a worm (as represented in _fig._ 93.) through the horizontal generator or receiver; and, tapering gradually, until reduced to very small dimensions, it finally issues into the chimney G. The air in passing along this tube, imparts its heat to the water by which the tube is surrounded, and is brought to a considerably reduced temperature when discharged into the chimney. The cylinder, which is represented at K, works one pair of wheels, by means of a bell-crank, the other pair, when necessary, being connected with them.

In this engine, the magnitude of the surface of burning fuel on the grate-bars is less than two square feet; the surface exposed to radiant heat is nine and a half square feet; and the surface of water exposed to heated air is about thirty-three square feet.

The superiority of the Rocket may be attributed chiefly to the greater quantity of surface of the water which is exposed to the action of the fire. With a less extent of grate-bars than the Sanspareil, in the proportion of three to five, it exposes a greater surface of water to radiant heat, in the proportion of four to three; and a greater surface of water to heated air, in the proportion of more than three to two. It was found that the Rocket, compared with the Sanspareil, consumed fuel, in the evaporation of a given quantity of water, [Pg351] in the proportion of eleven to twenty-eight. The suggestion of using the tubes to conduct through the water the heated air to the chimney is due to Mr. Booth, treasurer of the Liverpool and Manchester Railway Company.

(191.) The object to be effected in the boilers of these engines is, to keep a small quantity of water at an excessive temperature, by means of a small quantity of fuel kept in the most active state of combustion. To accomplish this, it is necessary, first, so to shape the boiler, furnace, and flues, that the water shall be in contact with as extensive a surface as possible, every part of which is acted on, either immediately, by the heat radiating from the fire, or mediately, by the air which has passed through the fire, and which finally rushes into the chimney: and, secondly, that such a forcible draught should be maintained in the furnace, that a quantity of heat shall be extricated from the fuel, by combustion, sufficient to maintain the water at the necessary temperature, and to produce the steam with sufficient rapidity. To accomplish these objects, therefore, the chamber containing the grate should be completely surrounded by water, and should be below the level of the water in the boiler. The magnitude of the surface exposed to radiation should be as great as is consistent with the whole magnitude of the machine. The comparative advantage which the Rocket possessed in these respects over the other engines will be evident on inspection. In the next place, it is necessary that the heat, which is absorbed by the air passing through the fuel, and keeping it in a state of combustion, should be transferred to the water before the air escapes into the chimney. Air being a bad conductor of heat, to accomplish this it is necessary that the air in the flues should be exposed to as great an extent of surface in contact with the water as possible. No contrivance can be less adapted for the attainment of this end than one or two large tubes traversing the boiler, as in the earliest locomotive engines: the body of air which passed through the centre of these tubes had no contact with their surface, and, consequently, passed into the chimney at nearly the same temperature as that which it had when it quitted the fire. The only portion of air which imparted its heat to the water [Pg352] was that portion which passed next to the surface of the tube.

Several methods suggest themselves to increase the surface of water in contact with a given quantity of air passing through it. This would be accomplished by causing the air to pass between plates placed near each other, so as to divide the current into thin strata, having between them strata of water, or it might be made to pass between tubes differing slightly in diameter, the water passing through an inner tube, and being also in contact with the external surface of the outer tube. Such a method would be similar in principle to the steam-jacket used in Watt's steam engines, or to the condenser of Cartwright's engine already described. But, considering the facility of constructing small tubes, and of placing them in the boiler, that method, perhaps, is, on the whole, the best in practice; although the shape of a tube, geometrically considered, is most unfavourable for the exposure of a fluid contained in it to its surface. The air which passes from the fire-chamber, being subdivided as it passes through the boiler by a great number of very small tubes, may be made to impart all its excess of heat to the water before it issues into the chimney. This is all which the most refined contrivance can effect. The Rocket engine was traversed by twenty-five tubes, each three inches in diameter; and the principle has since been carried to a much greater extent.

The abstraction of a great quantity of heat from the air before it reaches the chimney is attended with one consequence, which, at first view, would present a difficulty apparently insurmountable; the chimney would, in fact, lose its power of draught. This difficulty, however, was removed by using the waste steam, which had passed from the cylinder after working the engine, for the purpose of producing a draught. This steam was urged through a jet presented upwards in the chimney, and driven out with such force in that direction as to create a sufficient draught to work the furnace.

It will be observed that the principle of draught in the Novelty is totally distinct from this: in that engine the draught is produced by a bellows worked by the engine. The question, as far as relates to these two methods, is, whether more power [Pg353] is lost in supplying the steam through the jet, as in the Rocket, or in working the bellows, as in the Novelty. The force requisite to impel the steam through the jet must be exerted by the returning stroke of the piston, and, consequently, must rob the working effect to an equivalent amount. On the other hand, the power requisite to work the bellows in the Novelty must be subducted from the available power of the engine. The former method has been hitherto found to be the more effectual and economical.

The importance of these details will be understood, when it is considered that the only limit to the attainment of speed by locomotive engines is the power to produce, in a given time, a certain quantity of steam. Each stroke of the piston causes one revolution of the wheels, and consumes four cylinders full of steam: consequently, a cylinder of steam corresponds to a certain number of feet of road travelled over: hence it is that the production of a rapid and abundant supply of heat, and the imparting of that heat quickly and effectually to the water, is the key to the solution of the problem to construct an engine capable of rapid motion.

The method of subdividing the flue into tubes was carried much further by Mr. Stephenson after the construction of the Rocket; and, indeed, the principle was so obvious, it is only surprising that, in the first instance, tubes of smaller diameter than three inches were not used. In engines since constructed, the number of tubes vary from ninety to one hundred and twenty, the diameter being reduced to two inches or less; and in some instances tubes have been introduced, even to the number of one hundred and fifty, of one and a half inch diameter. In the Meteor, twenty square feet are exposed to radiation, and one hundred and thirty-nine to the contact of heated air; in the Arrow, twenty square feet to radiation, and one hundred and forty-five to the contact of heated air. The superior economy of fuel gained by this means will be apparent by inspecting the following table, which exhibits the consumption of fuel which was requisite to convey a ton weight a mile in each of four engines, expressing also the rate of the motion:— [Pg354]

————————————————————————————————————————————————————————————
| Average Rate of | Consumption of Coke
Engines. | Speed in Miles per | in Pounds per Ton
| Hour. | per Mile.
————————————————————————————————————————————————————————————
No. 1. Rocket | 14 | 2·41
2. Sanspareil | 15 | 2·47
3. Phœnix | 12 | 1·42
4. Arrow | 12 | 1·25
————————————————————————————————————————————————————————————

(192.) Since the period at which this railway was opened for the actual purposes of transport, the locomotive engines have been in a state of progressive improvement. Scarcely a month has passed without suggesting some change in the details, by which fuel might be economised, the production of steam rendered more rapid, the wear of the engine rendered slower, the proportionate strength of the different parts improved, or some other desirable end obtained.

Engines constructed in the form of the Rocket, were subject to two principal defects. The cylinders, being placed outside the engine, were exposed to the cold of the atmosphere, which produced a waste of heat more or less considerable by condensation. The points at which the power of the steam to turn the wheels was applied, being at the extremities of the axle and on the exterior of the wheel, a considerable strain was produced, owing to the distance of the point of application of the power from the centre of resistance. If it were possible that the impelling power could act in drawing the train at all times with equal energy on both sides of the engine, then no injurious strain would be produced; but from the relative position of the points on the opposite wheels to which it was necessary to attach the connecting rods, it was inevitable that, at the moment when one of the pistons exerts its full power in driving the wheel, the other piston must be altogether inactive. The impelling power, therefore, at alternate moments of time, acted on opposite wheels, and on each of them at the greatest possible distance from the centre of the axle.

(193.) The next step in the improvement of the machine was made with a view to remove these two defects. The cylinders were transferred from the exterior of the engine to the [Pg355] interior of the casing called the smoke-box, B, _fig._ 94., which supports the chimney, and which receives the heated air issuing from the tubes which traverse the boiler. Thus placed, the cylinders are always maintained as hot as the air which issues from the flues, and all condensation of steam by their exposure is prevented. The piston-rods are likewise brought closer together, and nearer the centre of the engine: the connecting rods, no longer attached to the wheels, are made to act upon two cranks constructed upon the axle of the wheels, and placed at right angles to each other. From the position of these cranks, one would always be at its dead point when the other is in full action. The action of the steam upon them would, therefore, be generally unequal; but this would not produce the same strain as when the connecting rods are attached to points upon the exterior of the wheels, owing to the cranks being constructed on the axle at points so much nearer its centre. By this means it was found that the working of the machine was more even, and productive of much less strain, than in the arrangement adopted in the Rocket, and the earlier engines. On the other hand, a serious disadvantage was incurred by a double-cranked axle. The weakness necessarily arising from such a form of axle could only be removed by great thickness [Pg356] and weight of metal; and even this precaution, at first, did not prevent their occasional fracture. The forging of them was, however, subsequently much improved: the cranks, instead of being formed by bending the metal when softened by heat, were made by cutting the square of the crank out of the solid metal; and now it rarely happens that one of these axles fails.

The adoption of smaller tubes, and a greater number of them, with a view more perfectly to extract the heat from the air in passing to the chimney, rendered a more forcible draft necessary. This was accomplished by the adoption of a more contracted blast-pipe leading from the eduction-pipes of the cylinders and presented up the chimney. A representation of such a blast-pipe, with the two tubes leading from the cylinders and uniting together near the point, which is presented up the chimney, is given at _p p_ in _fig._ 104. The engine thus improved is represented in _fig._ 94.

A represents the cylindrical boiler, the lower half of which is traversed by tubes, as described in the Rocket. They are usually from eighty to one hundred in number, and about an inch and a half in diameter; the boiler is about seven feet in length; the fire-chamber is attached to one end of it, at F, as in the Rocket, and similar in construction: the cylinders are inserted in a chamber at the other end, immediately under the chimney. The piston-rods are supported in the horizontal position by guides; and connecting rods extend from them, under the engine, to the two cranks placed on the axle of the large wheels. The effects of an inequality in the road are counteracted by springs, on which the engine rests; the springs being below the axle of the great wheels, and above that of the less. The steam is supplied to the cylinders, and withdrawn, by means of the common sliding valves, which are worked by an eccentric wheel placed on the axle of the large wheels of the carriage. The motion is communicated from this eccentric wheel to the valve by sliding rods. The stand is placed for the attendant at the end of the engine, next the fire-place F; and two levers L project from the end which communicate with the valves by means of rods, by which the engine is governed so as to reverse the motion. [Pg357]

The wheels of these engines have been commonly constructed of wood with strong iron ties, furnished with flanges adapted to the rails. But Mr. Stephenson afterward substituted, in some instances, wheels of iron with hollow spokes. The engine draws after it a tender carriage containing the fuel and water; and, when carrying a light load, is capable of performing the whole journey from Liverpool to Manchester without a fresh supply of water. When a heavy load of merchandise is drawn, it is usual to take in water at the middle of the trip.

(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 extending 1-1/2 mile, 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, 21-1/2 miles an hour; fall of 6 feet in a mile,
25-1/2 miles an hour; on the rise over Chatmoss, 8 feet in a
mile, 17-5/8 miles 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:—

Level 17-5/8 miles per hour.
Fall of 4 feet in a mile 22
—— 6 22-1/2
Rise of 8 15

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 1500_l._ 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 the _speed_ of 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 a _full load_ of profitable carriage _from_ Manchester, about half the waggons _come 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, _coal_ is 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 use _coke_, 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 the _present time_, compared with what it was two years ago."

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

Miles.
Planet 9,986
Mercury 11,040
Jupiter 11,618
Saturn 11,786
Venus 12,850
Etna 8,764
——————
Making in all 66,044
——————

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

Miles.
Jupiter 16,572
Saturn 18,678
Sun 14,552
Etna 17,763
Ajax 11,678
Firefly 15,608
——————
Making in all 95,851
——————

(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. In _fig._ 97. is exhibited a vertical section of the engine made by a plane carried through its length; and in _fig._ 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. In _fig._ 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.

In _fig._ 101. is represented an elevation of the hinder end of the engine next the fire-box; and in _fig._ 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.

In _fig._ 103. is represented an elevation of the front of the engine next the smoke-box, showing the cylinder covers W, buffers T, &c.; and in _fig._ 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 branches S of the steam-pipe leading to the cylinders, the blast-pipe _p_, the cylinders H, and the chimney G.

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 at A, _fig._ 97. The fire-box consists of two casings of metal, one within the other. The fire-grate is represented at D. The tubes by which the products of combustion are [Pg366] drawn from the fire-box to the smoke-box F are represented at E. Upon the smoke-box is erected the chimney G. In the engine from which this drawing has been taken, and which was used on the London and Birmingham Railway, the boiler is a cylinder 7-1/2 feet long, and 3-1/2 feet in diameter. It is formed of wrought-iron plates 5/16 of an inch in thickness, overlapping each other, and bound together by iron rivets 7/8 of an inch in diameter and 1-3/4 inch apart. One of these rivets, as it joins two plates, is represented in _fig._ 95. The boiler is clothed with a boarding of wood _a_, 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.

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 in _fig._ 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 in _fig._ 96. These rivets are seen in section in _fig._ 97.

The internal fire-box C, _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 is 7/8.

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 at _f_ in _fig._ 97. The plates forming the bounding surfaces of the two fire-boxes are fastened together by stays represented at _k_ in _figs._ 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 in _fig._ 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.

LONGITUDINAL VERTICAL SECTION OF A LOCOMOTIVE ENGINE.]

LONGITUDINAL VERTICAL SECTION OF THE TENDER.]

PLAN OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.]

PLAN OF THE TENDER.]

ELEVATION OF THE HINDER END OF A LOCOMOTIVE ENGINE.]

CROSS VERTICAL SECTION OF THE ENGINE THROUGH THE FIRE-BOX.]

ELEVATION OF THE FOREMOST END OF THE ENGINE.]

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 at _l_, in _fig._ 97., and of which an end view is seen in _fig._ 102., are attached by bolts to it. These ribs are hollowed out, as seen in _fig._ 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 at _m_, _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-door _g_. 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 at E, _fig._ 97., and their ends are seen in the surface of the internal fire-box in _fig._ 102., and in the remote end of the boiler where they terminate in the smoke-box in _fig._ 104. These tubes are formed of the best rolled brass, and their thickness in the engine, to which we now refer, is 1/13 of 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.

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 at C. _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 was 1-5/8 inch. The distance between tube and tube was 3/4 of 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 at _o_ in their length in _fig._ 97., and an end view of them is seen in _fig._ 102. The smoke-box F, _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 in _fig._ 103., and in section _fig._ 104., rises the chimney G, fifteen inches diameter, and formed of 1/8 inch iron plates, riveted and bound round by hoops. It is flanged to the top of the [Pg371] smoke-box, as represented in _fig._ 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-dome T (_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 brass 3/8 inch 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 tube _d′_ (_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-pipe S, which traverses the whole length of the boiler. The steam rising from the boiler fills the steam-dome T, and descends in the funnel-shaped tube _d′_. 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-pipe _a_ is 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 spindle _a″_ of the regulator passes, and to its end is attached a winch _h′_, by which the spindle _a″_ is capable of being turned. This winch is limited in its play to a quarter of a revolution. The other end of the spindle _a″_ is attached to a plate _e′_ seen edgeways in _fig._ 97., and the face of which is seen in _fig._ 102.: this circular plate _e_ is 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-pipe S. This fixed circular plate is likewise pierced with two nearly quadrantal apertures, corresponding with those in the movable plate _e′_. When the movable plate _e′_ is turned round by the winch _h′_, 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-pipe S communicates with the funnel _d′_ by the two quadrantal apertures thus open. If, on the other hand, the winch _h′_ 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-pipe S and the funnel _d′_ 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 winch _h′_ of the regulator is moved from the former position to the latter, in every intermediate position the aperture communicating between the funnel _d′_ and the steam-pipe S will be less in magnitude than the complete quadrant. It will in fact be composed of two openings having the form of _sectors_ of 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-pipe S may be regulated by the winch _h′_.

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 in _fig._ 104. This cross pipe is itself flanged to two curved steam-pipes S (_fig._ 104.), by which the steam is conducted to the valve-boxes V 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 in _fig._ 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.