228 JOURNAL OF THE INST. OF LOCO. ENGINEERS.

THE MODERNBRITISH EXPRESS PASSENGERLOCOMOTIVE.

Paper read before the Institution by F. W. BEESLEY (Graduate), Glasgow, on 19th January, 1922, at Glasgow.

Paper No. 119." Between the built by George Stephenson and introduced for service on the Liverpool and Manchester Railway in 1829, and the present-day express passenger locomotive there is " a great gulf fixed." In appearance the locomotive built by Stephenson will not bear comparison, for example, with the massive and stately express main line recently constructed. " Picturesqueness " has not been sacrificed to design, for no one, however un- initiated, can see one of these triumphs of skill and thought without a feeling of admiration. From 1829 up to the present day the power of the passenger locomotive has gradually been increasing ; twc- engines giving place to four-cylinder compounds, and latterly the three-cylinder engine has come to the front in the form of compounds on the Midland Railway, " At- lantics " on the North-Eastern Railway, and more recently the new 4-6-0 type on the Caledonian Kailway. The first problems which face the designer of one of the present-day express locomotives are the fixed restrictions as to height, width and length, these being brought about by bridges, permanent way and sharp curves. The loco'motive is made up of three principal parts :- (I) The and , where the heat produced is used for the generation of steam ; (2) The cylinders and valves, where the energy in the steam is transformed into motive power ; and (3) The frame and on which the boiler and cylinders are carried, and by which the tractive force at the r'ail is transmitted to the drawbar con- necting engine and train.

* .4warded 2nd Prize for Graduate's Paper read before Scottish Centre. Silver Medal presented by Mr. David Smith, G. & S.W.R.

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Before taking each one of these parts and considering them in detail, it is advisahle to say a few words on the different types of main line locomotives which are at \present running on the various railways of this country.

The word ‘‘ type ” means the several arrange- ments adopted by the various railways. It does not, how- ever, follow that each railway company has the same tyw of locomotive for its standard main line work as the others. There are three types in use which may be said to be “ standard ” in this country. (Ij The four-coupled passenger, or 4-4-0 loco- motive, which has a leading bogie and four coupled wheels. This type is by far the most popular of the three. (2) The ‘‘ Atlantic,” or 4-4-2 type, which has a leading bogie, four coupled wheels and a pair of trailing radial wheels. This type is used when a large firebox is desired. It may be mentioned that, with the exception of those of the Lancashire and Yorkshire Railway, all “ Atlantics ” are outside cylinder engines. (3) The ten-wheeler, or 4-6-0 type, which has a leading bogie and six coupled wheels. This type is used extensively on most of the railways, and is found in the form of a two-cylinder, a three-cylinder, or a four-cylinder’ engine. On account of its long coupled wheelbase, the result is a large and long boiler and a big firebox. It may be of interest to note that at present there are 3,457 engines of the 4-4-0 type, 1,083 of the 4-6-0 typer and 293 of the 4-4-2 type, forming 32 per cent. of the grand total of tender engines in this country. Other types, smaller than those already mentioned, are used frequently on some railways for passenger trains- such as the 2-4-0’s on the Midland and London & North- Western Railways, and the 0-4-2’s on the London, Brighton & South Coast and the London & South-Western Railways. Some of the leading railways are using extensively very large tank engines for their main line work, e.g., the London, Brighton 81 South Coast and Midland Railway 4-6-4 or “ Baltic ” type tanks, and the Caledonian, Great Central, London, Brighton & South Coast, and London & North-Western 4-6-2 or “ Pacific ” type tanks. To return to the subject of analysing the locomotive. The modern locomotive boiler has several good points. For its size and weight it is a quick steam producer. It can easily be ‘‘ forced ” when occasion demands, and, as is obvious, its shape is remarkably well adapted for its par-

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ticular purpose. Otherwise it is expensive, and although several attempts have been made to improve it, the bosiler universally used by all railway companies to-day remains essentially an enlarged pattern of the “ Rocket ” boiler. The boiler is made up of three main com,panents-the firebox, the barrel and -which will now be described. The inner firebox is a large rectangular chamber, the front end being the tubeplate, and the back end the door- plate. The roof of the firebox is formed by a large plate, which is called the “ firebox crown.” In this country all these plates are made of the best capper, although in America they are nearly always made of mild steel. There are two reasons for coppef being used:- (I) Copper is a much better conductor of heat than steel. (2) It is able to withstand the great strains brought about by repeated expansion and contraction far better than steel, which has a tendency to crack, especially in the corners. The flat surfaces of the sides and ends of the copper box are supported by stays made of best rolled soft copper bars screwed into both copper and steel shell plates and riveted over. These stays suffer very severely, especially when steam is being raised, from the fact that the copper plates became very much hotter than the steel plates, and, having also a higher coefficient of expansion than steel, the copper plate expands vertically relatively to the steel, gush- ing up the inner ends of the stays and causing them to become bent or broken. The flat firebox roof is supported either by gilder stays, with feet resting on the tubeplate and doorplate and connected throughout their length ta the roofplate by screws; or by direct stays made of steel rods screwed into both copper and steel plates and held with nuts inside the firebox, and riveted over on the outside of the shell [plate, or throat plate as it is sometimes called, and the back plate which forms the end of the boiler and has the firehole cut in it. This “ shell ” is riveted to the inner firebox through what is known as the foundation ring, which is a forged steel or wrought-iron frame bent round to form a large rectangle embracing the bottom of the firebox. The wrapper plate has a manhoie on top of it, which is used for a seating for the safety valves. A firegrate forms the bottom of the firebox: This consists of a series of bars arranged langitudinally, with spaces between them sa as to allow a passage for the air

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 THE MODERN BRITISH EXPRESS LOCO.-BEESLEY. 23 I essential for the combustion of the fuel placed on top of the bars. The grate may be level or inclined at the back or front. It is the general practice here to place the firebox between the frames, and as the size of the grate is limited by the distance between the driving and trailing or the intermediate and trailing , as the case may be, it is obvious that unless some means were taken it would not be possible to burn enough fuel on such a small grate to produce the required amount of steam for the work'the engine has to do. This, however, is overcome by utilising the draught produced by the exhaust steam. Fixed to the bottom of the sides of the firebox by means of studs and nuts so as to be easily detached, is the ashipan, which is a box-like structure about a foot deep. It is provided with dampers, generally fixed at the front end on tender engines, but at the back as well on tank engines, which are required to run both ways. The ashpan is used to collect the ashes as they drop through the fire- bars, and also, when required, to prevent air entering through the firebars. By means of levers and catches in the , the driver is able to control the dampers. There is another component of the firebox which has not yet been mentioned, and without which the firebox would certainly not be complete. This is the firebrick arch, which is built up across the front part of the firebox, just below the bottom of the tubes, and rkaching over towards the firehole. It is inclined upwards, forming an arch across the box, thus its name. The arch deflects the fire over towards the back of the firebox, causing the heat to be more equally spread out over the whole of the inside of the firebox, and prevents cold air passing over and striking the ends of the tubes, thus reducing tube leakage. It has already been mentioned that the back ,plate of the firebox contains an opening which is called the " fire- hole." This is placed so as to be easily accessible from the footplate for the purpose of sho'velling in the coal and attending to the fire. Firedoors are not all of the same pattern, but a popular one is that which is hinged at the top and opens inwards. These are provided with a handle and catches so that the amount of opening can be regulated. A hinged plate, the size of which is practically the same as the firehole, ,prevents cold air entering, or heat escaping from, the firebox. Before leaving the firebox a few words should be said about the Belpaire firebox. In this box the outside wrapper plate is flat on top, while the inside one is parallel to it,

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 232 JOURNAL OF THE INST. OF LOCO. ENGINEERS. and these are tied together by direct stays, which are usually made of steel. It has the advantage of affording greater ease for cleaning out the top of the copper box. The boiler barrel of a locomotive consists of a cylin- drical shell of a diameter which varies from about 4ft. to sift. or over, and its length from roft. to 1Qft.-though some of the big are over 17ft. in length. Tho barrel is made up of steel plates, the thickness of which depends chiefly on the steam pressure and the diameter of the barrel. This barrel is made in two' or three rings, riveted transversely together, in the shape of a true circle, the longitudinal seams having inside and outside butt stra,p. Thirty or more years ago the steam pressure was about 140lbs. per square inch, but nolwadays it lies between the limits of 16olbs and z25lbs. per square inch. In the case of engines fitted with , such a high pressure is not used, because the increase in efficiency obtained from the superheated steam allows a reduction in the pressure to be made, which then varies from 16olbs. to 2001bs. per square inch. Inside the barrel there are a very large number of flue- tubes of a diameter which varies from Idin. to 2$in. out- side, the number being between 170 and 280, depending on the diameter of the barrel and the size of tube used. The reason for these tubes is to obtain as large a heating surface as possible. The hot gases coming from the fire- box transmit their heat to the water which surrounds the tubes. Iron, steel, brass or a hardened copper composition is used for making the tubes, but steel is generally em- ployed on account of its lower cost. The ends of the tubes are ex,panded tightly into the firebox and smokebox tube plate. This is done by special roller expanders. On top, at the centre of the boiler barrel, there is a manhole for what is called the , which has a removable cosver called the dome shell. The object of the dome is to provide steam space above the level of the water, thus ensuring dry steam. The dome contains the regulator by means o'f which steam is transmitted from the boiler to the cylinders. Having entered the regulator, the steam flows through the steam pipe to what is known as the T-piece in the smokebox ; here the steam pipe bifur- cates, one branch going to each of the two cylinders. These pipes pass downwards from the Tpiece, and are shaped so as to follow the ccmtour of the smokebox sides. Col>per js employed in the manufacture of the pipes, except wherk

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 THE MODERN BRITISH EXPRESS LOCO.-BEESLEY. 233 superheated steam is used, when they are made of steel, copper being an unsafe material in that case. The regulator head, which is inside the dome, has a slide valve or a double beat valve. In order to allow the steam to enter, this valve is raised by means of a vertical rod which has a small crank or eccentric at the bottom, this being fixed to the regulator rod, which terminates in the cab. This rod passes through a gland in the back firebox shell, and on the end of the rod is fixed the regulator handle, which is able to be moved by the driver. Thus the driver can control the movement of the valve in the dome and thereby the amount of steam admitted to the cylinders, The third and last component of the boiler is the smoke- box, which is the front ,portion of the boiler. The smoke- box is separated from the barrel by the front tubeplate. Inside the smokebox are the steam pipes, the blast pipe, and the petticoat pipe, or " hood " as it is sometimes called. As there is no pressure in the smokebox, thin steel plates are employed for its construction. The top part of the cylinder casting forms the bottom ,portion of the smokebox on an inside cylinder engine, but in the case of an outside cylinder engine a steel casting or a box-like structure made up of plates and angle-irons is placed between the frames. 'The blast pipe, which is made of cast-iron, has a nozzle at its top, and great care is taken that this nazzle is made so as to allow the column of escaping steam to fairly enter the barrel of the funnel, and not to come in contact with the base of the funnel. To this end the pipe, for about the last foot of its length, is made vertical and exactly central with the . This pipe is the means of an outlet for the steam exhausted from the cylinders into the air, while the suction caused by the escaping steam generates the hecessary draught on the fire, and at the same time pulls the hot gases through the boiler flue-tubes. When lighting the fire, it is necessary that some kind of artificial draught should be created. This is produced by means of the blower which is fixed in the smokebox. A circular tube ring with a series of holes in its ulpper surface is fitted round the blast pipe outlet and connected by a pipe to the blower cock. The idea of the holes is that when the steam is admitted it will escape through them and pass up the funnel, thus causing the required dkaught. The blower is controlled by the engineman by a handle in the cab. The next few paragraphs deal with what is perhaps one of the most imprtant parts of the equipment of the present-day express engine, namely, the superheata. It is advisable to deal with the here as it is fitted

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in the boiler and smokebox. Practically all the main line locomotives constructed during the past few years have been fitted with superheaters, and these have proved to be extremely efficient machines, capable of hauling heavy loads over severe gradients. The superheater has come to stay. The distinction of making high degree superheating a success in locomotives was won by Herr Schmidt, of Cassel, who, after many experiments, devised a practical design which is used extensively in this country to-day. When an engine is superheated it is done with the view to impart- ing a higher temperature to the steam than that usually associated with its pressure. This is accomplished by causing the steam, on ,passing between the regulator and the cylinders, to absorb heat from the hot gases issuing from the firebox. Superheating has several advantages :- (I) Condensation in the cylinders is prevented, and thus fuel economy is brought about. (2) The volume of superheated steam is considerably greater than that of saturated steam. (3) The tractive force of the locomotive is greatly in- creased, thus the consumption of coal and water is decreased. lwo types of superheaters are in use at present-the Schmidt and the Robinson. The difference between the types is chiefly the arrangement of the header, and the method used in regulating the heat. In both systems fire-tubes varying from 44in. to 5tin. outside diameter are substituted for the flue-tubes in the upper part of the boiler, as it is there that the hottest gases are found. Inside the fire-tubes are placed what is known as the superheater elements, each of which consists of a tube having an outside diameter of Iain. to Iiin. These elements are bent so as to form four parallel tubes; thus in the Schmidt system the steam passes four times through the fire-tubes, i.e., from one compartment in the header to the firebox end, returning to the smokebox again back to the firebox, and finally it passes back into another compartment of the header, after which it flows through the steampipes to the cylinders. In order to prevent the elements being overheated when the engine is at rest, dampers are sometimes fitted, which consist of iron plates in the smokebox extending from the bottom row of fire-tubes to the header. When the engine is running with steam on, the damper is kept open by means of steam in a small cylinder fitted on the outside of the smokebox. The damper is connected to the

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piston of the cylinder by means of levers and a balance weight. The amount of opening of this damlper is regulated from the cab by means of a rod. Directly steam in the cylinder is shut off, the piston is released and the damper is closed automatically by the balance weight. The Robinson superheater, as already mentioned, differs from the above chiefly in the construction of the header. Elements of the Schmidt type are secured into the header compartments by means of a plate and a nut and bolt, while the Robinson elements are expanded directly into the header, which is arranged with a door to give access to the element ends. Again, in the " Robinson " the dampers and levers are done away with, and in their place j ts of steam from small pipes known as draught retarders are employed. To permit of the superheat being indicated in the cab a pyrometer is fitted. The temperature of the steam is usually maintained at about 650°F. It may be added that dampers and draught retarders are often omitted now. 'There now only remain the funnel, safety valves, whistle, cab and cab mountings to describe, so as to finish with the boiler. The funnel, which is situated on top at the centre of the smokebox, may be either parallel or tapering in shape. Its length obviously depends upon the height of the boiler from rail level, as there is a fixed loading gauge in this country which only permits of a little over 13ft. passing under it. The tapering form, which is larger at the top than the bottom, is said to help the draught by giving a better passage for the gases. The design used for the top of the funnel affects the direct discharge of the steam. To prevent excess pressure in the boiler, safety valves are fitted. Two, three or four valves are used, and the precaution is taken of bolting them up in a casing. The lift of these valves is controlled by springs and a lever, which bears directly upon them. On tQp of the firebox, between the safety valves and the cab stormboard, there is usually a mounting for the whistle. Various kinds of whistles are in use at present; hut two kinds will be shortly dealt with. The first type consists of a bell made of gunmetal, in- verted with its moath downwards so that its sharp edge is immediately over an annular opening in the base of the whistle. The steam escapes oat of this hole and strikes against the sharp edge, thus causing the bell to vibrate violently, and in so doing to emit sound. Steam is admitted to the whistle through a valve which is kept closed by the

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steam pressure. To open a valve a lever is provided in the cab. The second type, which is exactly similar in its actions as the previous one, has a long pipe instead of a bell, and the same result is obtained, the sound being more like a liner’s syren. This type is employed throughout the Caledonian Railway. At the firebox end of the engine is situated the driver’s cab, the back plate of the firebox having all the cab mount- ings on it. Very different are the present-day cabs to those of seventy years ago, when a front sheeting or stormboard and windows sufficed, leaving the driver and fireman ex- posed to the weather. Nowadays everything possible is done for the comfort of the driver and his mate, this being well observed in the spacious large-roofed and side-window cabs of the Great Eastern, North British, and North- Eastern Railways. With regard to the mountings and pipes, most cabs are similar to each other, so if a few words are said about one of the cabs of an express locomotive on a prominent railway a fairly good idea of one can be formed. In order to keep the heat in to a certain extent, asbestos clothing is placed on the back-plate of the firebox, and over this is put the back or cab sheeting. This is screwed on to the last hoop on the firebox clothing, so as to make it firm. In the centre is the regulator, g!and, shield and handle ; om either side are two water-gauge cocks, one at the bottom and one at the top, placed a fixed distance apart, while a glass tube connects them, protected by shields. There is a nipple on one of the top cocks for the pipe to the pressure gauge, and the two bottom ones have nipples for drippipes. The stcam sanding cock is on the left-hand side, and serves both Ieading coupled wheels. Two Gresham and Craven hot-water , one on the left and one on the right side, are mounted. Each of these has two pipes, one for the water overflow and the other for the feed from the tender. A pipe is fitted to the top of one of the injectors, to which is attached a hose used for spraying the coals in order to keep down the dust. On the right-hand side is placed the combined lubricator and Westinghouse brake pump cock. A steam heater cock and gauge are fitted for the purpose of heating the carriages. In the case of a superheated engine, the damper rod, lever and catches are fitted on to the right-hand cab side. Two brakes are fitted in this particular case, the Westinghouse and the vacuum brakes, wlth corresponding gauges. Power is obtained from compressed air and atmospheric pressure respectively. A donkey pump is fixed

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 THE MODERS BRITISH EXPRESS LOCO.-BEESLEY. 237 on to the footplate of an engine using the Westinghouse brake, and this pump stafts and stops automatically, pumping in air up to a certain pressure. Often steam brakes are used in connection with the vacuum brake ; the former is used for engine and tender, while the latter is used for the train. The steam reversing lever and cylin- ders, as already mentioned, are fitted in the cab, while the firedoor and gear are situated in the backplate of the firebox. Tool boxes, fog signal box, lamp brackets, and the driver’s seat complete the cab fittings. Number plates are screwed on the outside of the cab sides with the company’s name and date of building on them. In order to reduce-the loss of heat from the boiler by radiation, asbestos mattresses or other insulating material are placed over the boiler plates and covered by thin steel sheets secured by bands and clips. This finishes with the boiler, but mention should be made of the method of fixing it into the framing. It is essential that allowance should be made for the expansion of the boiler, which is sometimes as much as 5/16in. The boiler is fastened rigidly to the cylinder casting at the front end, while at the firebox end expansion brackets are used. These consist of an angle iron riveted to the outer firebox shell, just about level uith the top of the frame. The angle iron rests on a level bed provided for it, and along which it can slide. A grooved block, fitting lightly upon its upper surface, prevents it rising. The engine “ proper ”--or the cylinders, valves and motion-next claims attention, being one of the three prin- cipal components of the locomotive. There are two-cylinder, three-cylinder and four-cylinder engines running in this country at the present time. Cylinder diameters vary from rgin. to azin. in the case of two-cylinder engines, but 16in. is a maximum in the case of four-cylinder engines. A stroke of 26in. is very common with all railway companies, though 28in. and 30in. are sometimes used. Nowadays there are two kinds of $main line engines running :- (i.) The engine using saturated steam and having slide valves and Stephenson’s link motion or Allan’s straight link motion. (ii.) The engine using superheated steam and having piston valves and Walschaert’s or a rocking shaft . The cylinders of a two-cylinder engine may be either placed inside or outside the frames, and both methods have their advantages. Inside cylinders are naturally placed

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closer together, and so the rods and motion are less likely to sway about, whereas outside cylinders afford a far easier examination of the motion to be made, since it is very cramped when placed inside the frames. Cylinders are made of a special brand of hard cast iron. They have covers fixed to each end of them by means of studs, but sometimes the back covers are cast solid with the cylinders. Projections cast on the back covers allow the slide bars to he fastened up. Water collects in the cylinders, and if there were no means of escape for it, serious damage might be done, so that each cylinder is fitted with tno drain cocks, one at each end. These are joined together by a rod, and by means of another rod, brackets, a lever, and a long rod running into the cab, the driver can open or shut them. When they are opened the steam in the cylinders blows the water out. Cast iron is used for the pistons, which are turned so that their diameter is xery slightly less than that of the qlinders. In order to prevent leakage of steam, the pistons are fitted with cast-iron rings uhich fit into grooves in the piston. IVhen the piston is in the cJlinder these rings spring outn ards, thus ensuring a perfectly tight fit between the piston rings and the cylinder x\alls. The piston is connected to the piston rod, made .of steel, and fitted with a conical end by means of a large brass nut and a split pin. This rod passes through the back cover of the cylinder, where there is a stuffing box or gland containing the packing to prevent the steam leaking out, to the crosshead, which, in the case of an inside-cylinder engine, consists of two slide-blocks, each running between tmo slide bars. An outside-cylinder engine has rather a different method. The bars are placed one above and the other below the piston rod, while the crosshead has a slipper top and bottom, and works between them. Great care is taken when buildipg the engine to see that these bars are properly lined up. A large inside-cylinder engine has only a limited amount of space for the cylinders, so that it is often the custom to place the valves above or below them. The cylinders are bolted to the frames by driving fit bolts, as there must be no slackness between cylinders and frame. Outside cylin- ders are cast separately and boltsd to the outside of the frames. Movement is transmitted to the valves by means of what is known as the " motion." Motions or valve gears are many and varied, but two types which are extensively used will be briefly described.

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The first one is what is known as “ Stephenson’s link motion. ” This motion, however, is gradually being sup- planted, especially in outside-cylinder engines, by Walschaert’s valve gear, which will be described later. Stephenson’s motion has two eccentrics to each cylinder. The eccentric is made up of two parts-the sheave, or central piece, which revolves inside the eccentric strap. The important thing to observe is that the sheave is not keyed centrally on to the so that a to-and-fro motion is imparted to the eccentric rod, the other end of which is joined by means of a pin to the expansion link. Similarly, the other rod is moved by the other eccentric. ‘These rods are known as the fore-gear and back-gear rods, the fore- gear rod being almost invariably attached to the top of the link, and the back-gear rod to the bottom of the link. The latter has a long cur\,-d slot machined in it, into which a machined block known as a die-block fits. This block takes the end of the valve spindle, and is free to move in the curved slot of the link. The lifting link is attached to the expansion link by means of a long pin to arms which are forged solid with the reversing shaft. The latter is carried on brackets bolted to the frames on either side. These arms lie almost horizontally, whilst another arm of the shaft points upwards, and is connected by means of a pin to the long reversing rod, which is attached to the reversing lever in the cab. The lever has a trigger con- nected to a rod, of which the bottom end works in notches in a curved quadrant. When the reversing rod is pushed forward, Le., towards the smokebox, the horizontal arm of the shaft is pushed down, which in turn moves the lifting link down and the expansion link with it. Now the eccentric rods are connected to the expansion link; thus they will also move downwards, so that the result is the fore-gear rod is brought practically into a straight line with the valve spindle, and the movement of the valve is done chiefly by the fore-gear rod and eccentric. The valve has been moved forward by the spindle, thus giving the engine motion, funnel first. When the’engine is required to run backwards, i.e., tender first, the reversing rod is moved to the back notch of the quadrant in the cab, and the movements of the rods and levers are exactly opposite to those already described. The fore-gear rods will be raised until the back-gear rods are nearly in line with the valve spindle. It would be a great strain on the driver if he had to pull up all the weight of the rods and levers when reversing, SO the reversing shaft has another arm forged on it, pointing towards the firebox, to the end of which is attached a large

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balance weight. On many engines a screw wheel is used instead of the lever. Walschaert’s valve gear, which is now used frequently, has only one eccentric and a slot link. The travel of the valve is controlled from two separate movements-one from the crosshead and the other from an eccentric wGch is fixed on the crank axle in the case of an inside motion, or by a returned crank fixed to the driving crank pin for an outside motion. By means of a system of levers, these two motions are combined, so as to give the desired motion to the valve. The crosshead has an arm which is carried down below the slide bar to a suitable distance, where it is con- nected to a union bar, the other end of which is joined the bottom of what is called the combination lever, having two holes at the top end. When the valve has outside admission, the valve spindle is attached to the top one, and the radius rod to the hole just below it, and conversely for valves with inside admission. This radius rod is joined at the other end to the die-block, this being allowed to move up and down in the slot link, which oscillates about its middle point. At the lower end of the link is fixed the eccentric rod, so that when the crank revolves the link is made to vibrate backwards and forwards about its fixed1 centre. If the engine is in the fore-gear, the radius rod is preferably at the bottom of the link. When it is reversed, the radius rod will thus be at the top of the link. One of the advantages of this motion is that, on account of the reducing effect of the combination lever, the valve move- ments actuated by this motion are not so liable to become deranged by wear. Two kinds of valves are used on express locomotives- slide valves and piston valves. The slide valve consists of a rectangular casting made of either cast iron or hard gun- metal. There are Ranges on either side in order to cover the cylinder ports as it passes backwards and forwards over them, whilst the central portion consists of a cavity, ribs being cast across it for strengthening it. The valve is fitted into a buckle, which is formed in one with the spindle. The latter passes through a gland and is attached to the spindle guide by its tapered end entering into a socket, the twe being held together by a cotter. Piston valves were first used fifty years ago, when they consisted of two solid pistons which fitted into a cylindricar chamber, no allowance being made for the water which accumulated to escape. In 1888 Mr. Smith, of the North-

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Eastern Railway, invented a piston valve in ‘which the pistons had collapsible rings. One of the best known patterns in use nowadays is that designed by Mr. J. G. Robinson, Chief Mechanical Engineer, Great Central Railway, for the use of superheated engines. This pattern consists of two pistons, one for each port, connected by a stem. Each piston has two discs, and between them are placed cast-iron packing rings. These valves differ from the slide valve in that they have inside steam admission, i.e., steam is admitted between the valve piston heads and exhausted outside them. Thus, if the piston moves to the right, steam will enter the right-hand port and exhaust from the left-hand port. The great advantage of the inside admission piston valve is that it keeps highly superheated steam away from &he valve spindle glands, thus reducing steam leakage. Piston valves have no large unbalanced surface, exposed to steam pressure, so that it takes less power to move them Phan the slide valves, and thus there is less wear and heating af eccentrics and pins. When an engine is running with steam shut off and the motion left in gear, it has a tendency, at each piston stroke, to draw air from the steam chest and discharge it up the funnel, thus forming a partial vacuum. To overcome this, a relief or “ snifting ” valve is fitted to the chest, the other end of the valve being free to the atmosphere to allow the air to enter into the chest and so destroy the partial vacuum. Piston valves require careful lubrication, or they become heated and seize. Many superheated engines are fitted with a mechanical lubricator for the valves and cylinders. One of the best known is “ Wakefield’s mechanical lubricator.” rhi,s consists of a rectangular iron chamber situated on the platform near the motion in order to allow the pipes to be arranged as easily as possible. Inside, at the bqttom, there are two rows of little pumps worked on the eccentric system by means of a ratchet and lever. This lever is given the required angular travel through a simple system of links connected to a moving part of the engine, e.g., one of the crank pins, or the reversing link, or some other part with a fixed travel. At the top of the box inside there rests a tray made of gauze, so that when the oil is poured in all dirt is left behind, and there is no chance of the pumps becoming clogged up. The lubricator can have from four to ten leads, and a lead for steam to heat the oil when it becomes thick. There is one disadvantage to this lubricator which should be mentioned. When the engine, with a heavy

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 242 JOURX.\L OF THE INST. OF LOCO. ENGINEERS. train, is on a stiff incline and needing oil constantly, the speed is slow ; that is, th,e coupled wheels are going slower, while the lubricator arm is moving slower also, so that the supply of oil is lessened. Directly, however, the engine is on the down grade and not requiring so much oil, the speed is considerably faster ; the lubricator is therefore also moving faster and the supply of oil is increased. Many locomotives are fitted with the sight feed lubri- cator, which is fixed in the cab. The oil is put in a cylin- drical chamber to which steam is admitted, and condenses, displacing the oil in so doing. This flows down a pipe and comes in contact with a jet of steam, thence it is carried to the valves and pistons. As the oil is displaced it passes, drop by drop, up through a sight tube, which is filled with con- densed water, thus being visible to the driver. Lubrication is most essential to the locomotive, and always before starting on a long run the driver makes a careful examination to see that all the oil cups are filled and the " sq'phons '' in their right places. The motion and the journals are all carefully attended to, so that there is no chance of heating or seizing due to want of lubrication. The last principal part of the locomotive, which consists of the frames and wheels, has other important parts attached to it, viz., axles, springs, sand-boxes and brake gearing. In the ex,press locomotive the frames are composed of two long steel plates Iin. to IBin. in thickness, one on either side of the engine. Recesses known as horns, throjugh which the axles pass, are cut out of each of the solid plates. These two frames must be connected together by cross stays, in order to give them lateral stiffness, and to keep them at the proper distance apart. At the very front of the engine is the buffer-beam, which is a steel plate riveted by means of angle irons to the frames. Two buffers, the draw-hook and screw-coupling, vacuum and Westinghouse pipes brackets are fitted on tot the beam. Immediately behind this beam is the cylinder casting, which forms a very strong connection between the frames. Next to this and between the cylinders and the leading coupled axle is the motion- plate, to which the slide bars are fixed. Just in front of the firebox there is a stay formed of a steel plate and angle irons, or a steel casting. Lastly, the frames are firmly joined together at the back end by a box casting known as the drag-box, which contains the draw- gear and blocks for coupling-up to the tender, while under- neath this box is bolted the brake cylinder and the Westing- house air reservoir. The frames are bent slightly inwards

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 THE MODERN BRITISH EXPRESS LOCO.-BEESLET. 2.13 at the front end, so as to allow enough lateral movement of the bogie wheels. Steel castings known as horn-blocks are firmly bolted to the frames, and fitted carefully into the horns. These blocks have planed rectangular faces, in order that the axle- boxes can slide freely up and down them. At the bottom ends the blocks are tied together, to prevent any spreading out, by iron recessed bars known as “ guard,plates ” or “ horn-keeps. ” The axleboxes are heavy and rectangular, and are made Of iron, steel, or gunmetal. Recesses are fitted on each of their outer side surfaces, so that they may fit over the horn- block’s faces. This prevents the axleboxes from moving more than an exceedingly small fraction of an inch. The steel boxes are machined inside to receive a casting of gun- metal known as the ‘‘ brass,” which is bored out to a slightly larger radius than that of the journal, and rests directly upon it. The “ brass ” is generally lined with white metal, which reduces friction if the lubrication is not quite right. At the top the box is hollowed out to form an oil reiervoir, while the bottom is closed up by a cast-iron keep which serves as the lower oil reservoir. A spring pad, saturated nith oil, is placed in this keep, and the springs keep the pad against the journal, so that the bottom of it is alwajs lubricated. Axiebox and keep are kept in position by one or two pins, which pass through them both. If one pin is used, it is made stout enough to hold a spring con- nection as well, when the spring is underneath the box. An eye bolt with a long head bored out to take the spring pin forms this connection. The spring is connected to the frame by two brackets riveted to the frame on either side of the centre of the axle. Oval holes are made in the bottom ends of these brackets, so as to allow the spring hangers to pass through. The hangers are secured to the top ends of the springs by pins, and below the brackets by double nuts. S,prings, which lessen the shocks received by wheels when running, are of several forms, those already described being laminated ; but spiral springs are often used, especi- ally for the driving wheels. The major part of the engine is carried on springs, but there is one important part which is not “ spring- borne,” and this consists of the axles, wheels, cranks and eccentrics. Wheel centres are made of steel castings, while the tyres are of hard steel, which is rolled from a solid ham- mered ingot, so that no weld is needed. The tyres are

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 244 JOURNAL OF THE INST. OF LOCO. ENGINEERS. shrunk on to the wheel centres and secured by a fastening ring or studs. Spokes radiate from the boss of the wheel to the rim. The number used depends on the size of the wheel, but they are generally placed about roin. or IIin. apart at the rim. Driving and coupled wheels of an express loco- motive vary in diameter from 6ft. to 73ft. Large wheels such as the famous 8ft. Great Northern singles are obsolete, and 6+ft. to 7ft. may be taken as a fairly good standard size. Axles are made of steel, all being straight axles excel@ the crank axle of the driving wheels; but this will also be straight if it is an outside cylinder engine. There are two portions at each end of the axle, and these have to be very carefully turned to the exact size. They are the ‘‘ wheel seats,” which are hydraulically pressed into the wheel centres, and the journals which revolve in the axlebox bear- ings. The crank axle is inore complicated. The connecting rod big ends have brasses fitted to the crank pins, while the crank webs connect the crank pins tot the axle body. Webs are flat, and may be either oval, circular or rect- angular with rounded ends. The crank and webs on one side of the engine are set at an angle of 90 degrees with those on the other, i.e., when one piston is at the end of its stroke, the other is almost in the middle. If both cranks were placed on the same side, or exactly on opposite sides of the axle, and the engine stopped, it would be impossible to start it again. In the case of a three-cylinder engine the cranks are set at 120 degrees with each other. The connecting rods, which are the connection between the crosshead and the crank axle, consist of flat rods the depth of which gradually increases from the crosshead or ‘‘ small end ” to the ‘‘ big end ” of crank. The driving wheels and the next one or two pairs of wheels are connected together by coupling rods. This is done in order to increase the weight available for adhesion en the rails. The weight on one pair of wheels should not exceed 20 tons in the heaviest locomotive, on account of the rails and under bridges. Connecting rods can either be from the leading pair of coupled wheels or the second pair, while some of the four-cylinder engines have all the cylinders driven off the leading wheels. Three-cylinder engines may be driven as follows: The outside cylinders off the second pair of wheels, and the inside cylinder off the leading wheel. It is necessary that the engine should run steadily, and not with too much oscillation at high 5peeds, so the pre- caution is taken of balancing the locomotive. Masses equivalent to the revolving masse5, viz., cranks, coupling rods are added to the rims of the driving wheels. These

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 THE MODERN BRITISH EXPRESS LOCO.-BEESLEY. 245 weights are chosen and placed so that the centrifugal forces upon them are opposite and equal to the resultant forces produced by the revolving parts. In addition, about two- thirds of the reciprocating weights are balanced in the same way. The front end of an express locomotive is carried on a separate four-wheeled truck or ‘‘ bogie,” for the purpose of obtaining lateral flexibility. The bogie “ centre ” is bolted underneath the cylinder casting, and a pivot is attached to it. This centre is machined, and its bottom surface rests on the top surface of the bogie casting, while the pin passes through both so as to allow one to rotate over the other. Washers and a split pin prevent the pin from slipping out. A second movement allows the top plate with the pivot to slide laterally over the bogie casting surface. The total amount of lateral sliding depends on the radius of the curves. This movement is controlled by side springs. The bogie frames are independent of the engine frames, but they are fitted with horn-blocks and keeps, while the axleboxes slide up and down the blocks, just as in the main frames. In order to prevent the coupled wheels of the engine from slipping when the rails are wet and greasy, sand is dropped on to the rails from the sand box, which is under the platform, or sometimes on the leading splasher. A pi,pe from the box to the rails permits of the sand being dropped. Nowadays steam is used to blow the sand on to the rails, but the sand should be extremely fine and dry, or it will clog up the valves. Having now given a resuml. of the development and construction of the present-day express passenger loco- motive, it is only necessary, in conclusion, to mention in a few words the functions of the tender. The tender is a separate tehicle, joined to the engine by drawbar and rubbing-blocks. It is designed for the pur- pose of carrying coal, water, tools and lubricants. Tenders hold from 2,000 to 5,000 gallons of water, and from five to seven tons of coal. Six-wheeled tenders are most common, but for long runs on railways having no water pick-up apparatus two four-wheeled are used to carry the tender. These last-mentioned tenders have the great disadvantage of being so heavy that their weight reduces the useful load which the engine can pull. Tenders generally have four frames, consisting of longi- tudinal plates each about gin. thick. Two frames are on either side, while the wheels run between them, the outer frames only being fitted with axlehoxes. These boxes differ

Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 4, 2016 246 JOV’KN~LOF THE INST. OF LOCO. ESGIKEEHS. from the engine boxes in that they are placed outside the frame, and therefore are outside the wheels. The bottom plate of the tank is extended to1 the front, so as to form the footplate, and has a hinged plate joined to it, which is let down to cover the gap between engine and tender. Tank sides are made of tin. plates, while the interior is strengthened by angle irons and stays. Plates riveted transversely across prevent “ backwash ” of the water. At the top, near the back, is a manhole for the purpose of filling the tank with water, and also to allow a man to get inside for repairs. Two %alves are fitted inside, at the front end, for the purpose of letting the water enter the feed-pipes, which are connected to the engine feed-pipes by flexible rubber pipes. These valves have strainers over them, to prevent any dirt from getting into the valve and stotpping the feed-water supply. Handles fitted on the footplate allow the driver to open and shut these valves. The coal is carried on top of the tank, which gradually slopes down to the footplate, so that the coal will always lie near the front. Rails are provided along the top edge of the tender, so as not to allow the coal to fall off. The engineer having now completed his task, the loco- motive is handed over to the painter, whoi, with the cdour and lines of the railway company to which the locomotive belongs, completes the work of months, and the locomotive and tender is ready for the road.

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