JULY 1914.

COMPOUND ARTICULATED .

DY ANATOLE MALLET, OF PARIS.

[ TTaizszafed.]

The imtlior asks permission to recall that at the Summer Meeting of the Institution held in Paris in 1879 he explained the applications which he had made of double expansion to locomotives. He is pleased he is able (35 years afterwards) to explain a particular type of compound at a similar Meeting. If rack lines, whose total length is not over a thousandth of that of railways all over the globe, be neglected, one may say that traction takes place solely through adhesion, that is, through friction between the rails and the tyres of the wheels under the action of the weight bearing on the axles. Friction is, after all, the universal principle of self-propelled locomotion on ewth. Animals we able to walk because their feet have n grip on tlie ground, while others cr:twl on their stomach. If the gradient is too severe, animals, such .‘is those which nature h:rs provided with claws, make use of them to support themselves without fear of slipping-a process which has been copied in the rack. The only thing is that in beings tlie progress is intermittent, whereas mech:mical progress takes place in a continuous way, by means of wheels, [THEI.MEcH.E.~

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 The tractive force of a locomotive is equal to the weight brought to bear on the rails by the tyres of driving and coupled wheels multiplied by the coefficient of friction for the parts in contact. This total weight is equal to the product of the number of coupled axles and the load on each axle (the latter load depending upon the conditions of settlement of the track). This weight, which was 3 tons per axle in 1825 on the Stockton to Darlington line, when railways were first started, increased to 8 tons in 1842, 14 tons in 1855, 16 tons in 1890, and has now reached about 20 tons on the more important lines. In the United States the weight goes up to 25 tons and more. For a long time, three was the maximum nnniber of axles coupled together, whereas now four and even five axles are coupled and only recently (though it was exceptional) six axles were reached. One can give a striking idea of the increase in weight and tractive power of engines for the last 85 years from the point of view of utilizing the track, in this way: (The author believes that this has not been published before). In 1839 an engine with two axles coupled, running on rails 17 kilograms per metre (34.3 lb. per yard), weighed 5 tons, which was equal to 300 times the weight of rids per metre. In 1846 an engine with three axles coupled, weighing 22 tons, ran on rails 35 kilograms per metre (70.53 lb. per yard). This came to 630 times the weight of rails per metre. In 1880 an engine with four axles coupled, weighing 56 tons, ran on rails 42 kilograms per metre (84.6 lb. per yard). This came to 1,330 times the weight of rails per metre. In 1911 a six-axle-coupled Golsdorf engine, weight 96 tons, on rails 48 kilograms per metre (96.77 lb. per yard), gave a ratio of 3,000. In 1911 as well, in the United St:ttes, a “Mallet” engine with ten axles coupled, weighing 245 tons (adhesive weight), represented N ratio of 4,600 times the weight of rails of 55 kilograms per metre (111 Ib. per yard); but this ratio, which is very high, is due to some extent to an exceptional weight per axle which is not to be found outside the United States.

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If adhesive force be taken as one-sixth of the weight, it will be found that the ratio of the tractive force at wheel trend to the weight of rails per metre has varied according to the values: 50 -105-225-333-750. The number of coupled axles, when coupling by outside rods requires that the axles must be absolutely parallel, is limited by the minimum radius of the curves on the line. In fact, for a certain radius there is a maximum distance between extreme parallel axles which must not subtend an angle greater than about 1". Beyond this, friction between the flanges of the wheels and the edge of the rails gives rise to severe wear of the surfaces in contact, and there is a chance that the flanges might jump the rails and cause derailments. It is true the flanges can be greased, but that is rather a poor solution to the problem. When the required tractive force necessitates an adhesive weight which, in view of the profile of the line and of other conditions, is greater than what the maximum number of coupled axles could bear, special assistance is required, such as pushers, two engines, motor driving wheels on tenders, twin engines or articulated engines. In articulated engines one can easily obtain the same adhesive weight (that is, the same tractive force) as with two engines, by distributing the axles on two frames coupled together, but capable of moving at an angle to one another, on curves. Such an engine with six axles, will, for example, take the same curve of minimum radius as would fit an ordinary engine with three axles coupled. This type of engine comprises rather a large number of different models, all of which have, as a common characteristic, an absence of enforced parallelism between the two groups of axles. But these types can be arranged into distinct categories, which rest partly on the number of cylinders driving the wheels, and partly on the disposition of the frame of the wheels, so that if these different categories be taken two by two, one gets the following four classes :-

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1. Locomotivcs with two movable trucks and only onc set of cylinders. 9. Locomotives with two movable trucks and two sets of cylinders. 3. Locomotive with only one truck and one set of cylindcrs. 4. Locomotive w-ith only one truck and two sets of cylinders.

The author will examine classes 2 and 4, because categories 1 and 3 are based on the use of certain mech:tnical transmissions, which, alone, would be n subject for a special Paper. Locomotives with two trucks and two sets of cylinders first appeared in the TTnited States in 1833 in a somewhat primitive form, due to Horatio Allen. But at the Soemmering Competition in 1851 locomotives of this t,ype were seen built on a practical plan. These engines were : the Seraing, built by the Belgian firm of the same name, with two barrels and two central fire-boxes, weight 56 tons ; and the Wiener-Neustadt, built by W. Gunther, of Vienna, with a. single boiler, weight 61 tons with full supply of fuel and water. The Seraing happem to be the prototype of the Pairlie engine, so far as essential dispositions :&reconcerned, in the same way as the Wiener-Neustadt is the prototype of the Meyer engine. It is absolutely necesbary to distirigiiiali dearly between the characteristics of these different engines. In fact, the author has had occasion to note that mistakes are made daily with regard to this, and they are even found in well-known works. Thus we read in a book on locomotives published in London in 1907, that the Mallet engine is nothing but the Meyer engine which appeared in 1867, to which M. Mallet has applied double expansion in 1884! So that the author thinks he should give diagrams, Fig. 1, showing the essential characteristics of each of these types, including the engine of the Chemin de fer du Nod, constructed in 1904 by the late M. Du Bousquet. The author will only casnally mention the Gnrmtt engine, which is characterized by the very gre:ht distance between the two driving trucks, thus allowing the boiler to be lodged between them, so that it may be fixed much lower, and have a great.er width than in the other types where it is above tJhe trucks?

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FIG.1.--(:ka,nctciistics of seveml Types of Two-track Aiticulnfcd Eii.giiws.

C. M eyer.

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The characteristics of the engines are as follows :- (A) Wiener-Neustrtdf.-Main frame carrying bufhg deviceb and driving apparatus, arid resting on the trucks on bupposts shaped horizontally like circular arcs-single boiler. (B) Seraing.-Main frame carrying buhg devices and driving apparatus and resting on the trucks on lateral supports ; the central points are independent of the coupling device. Boiler has a double central fire-box and double cylindrical barrel. (c) Neyer.--No main frame-the buffing devices and driving apparatus are carried by the trucks-the single boiler rests on the back truck on lateral supports, and on the front truck on a spherical pivot ; the two trucks are coupled by means of an arrow. (D) Nord.-Main frame carrying buffing devices and driving appnratus and resting on the back truck on lateral supports, and on the front truck on a spherical pivot. Single boiler. (E) FuirZie.--No main frame. The bufing devices and driving apparatus are fixed on the trucks, and the boiler, which has a central fire-box and two cylindrical barrels, rests on the trucks on circular supports, which also serve as couplings and have a certain elasticity laterally. (F) MaZZet.-This engine differs essentially from the others in that it has only one truck, placed in front and joined at the back to the main frame of the engine by a king pin. The front of the boiler rests on the truck on supports in the shape of arcs, whereas the back is fixed to the main frame. The author in studying this type reasoned on the following principle :-An engine with two axles coupled, driven by two cylinders and resting in front on a bogey with two axles as well, takes curves easily, but only part of its weight can be utilized for

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adhesion, and it cannot therefore exert a tractive force corresponding to its whole weight. If the wheels of the truck be driven by it pair of low-pressure cylinders of convenient size fixed to the truck, and if these cylinders be fed by the steam coming from the back high-pressure cylinders, a simple method will have been arrived at, giving the three following results :- (1) The engine will have been allowed the full benefit of its weight for adhesion, and at the same time it will have great flexibility. (2) The main difficulties which arise in the case of the Fairlie and Meyer types, and other types with two trucks, will have been removed in so far as the movable tubing of the new engine (which tubing is after all much less intricate than the other) will only take steam which has already been expanded to a pressure of 3 to 4 kg. per cm2 (42 to 57 lb. per square inch) at most. (3) A rather simple type of locomotive will thus have been created, which is justified by several advantages to be referred to later. This system, which the author advocated as far back as 1884, fulfilled the following conditions laid down by the Decauville firm in 1887 for locomotives running on 0.60 metre (1-foot 114-inch) tracks :- The engine had to take grades up to 1 in 12-5and haul weights nearly equal to its own, take curves of 20 metres in radius, and not weigh above 3 tons per axle, or 12 tons for four axles. Figs. 2 and 3 (page 436) show this engine. It is carried on four axles, two at the back under the fixed portion of the engine and two in front under the which articulates round a vertical hinge. The barrel of the boiler rests on the truck in a slide working in a circular groove carried by the truck as shown in plan in Fig. 2. The back cylinders work at high pressure, and the steam comes direct from the boiler, After having done its work, the steam goes to a central box containing a pipe curved in the shape of R swan’s neck, Fig. 3, which can turn round in that box, and the horizontal

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Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JULY 1Y14. COMPOUKD ARTICULATED LOCOYOTIVES. 437 part of which proceeds to the front where, through an up-take to be seen on the plan, it carries the steam to the low-pressure cylinders placed on the fore truck. The steam then escapes from these cylinders through a vertical pipe, which carries a knee-cap socket at its base, so that, with the aid of this combination, the high-pressure steam goes through fixed tubes only as in ordinary engines, and the pipes with movable joints take expanded steam only. This is very satisfactory

FIG.&-For Departmental Metre Gauge Railway, 1888.

0 I 2 3 4 SMCTRES I 1'1'1 I I I' I I I I I I I II I I I' I I tSFCET so far as tightness of joints is concerned, and presents great facilities for the use of superheated steam in those engines. The success of that first engine was complete, and the Decauville firm built a large number of them, which were sent to different countries to be used on agricultural farms, and on mining and forest w6rks, but the most important application was at the Universal Exhibition of 1889 in Paris, where six of those engines did the trafic on the Inner Circle of 0.60 metre (1-foot ll&inch) gauge laid down by the Decauville firm. They covered a total distance of 113,000 kilometres (72,000 miles), and carried more than 6,000,000 passengers with regularity and without accident. ?K

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The author wishes to recall that on Gth July 1889 he had the pleasure of showing, at the Petit Bourg Works, one of those small engines and of explaining its mechanism to a number of English engineers who had been invited over by M. Paul Decauville. Mr. John A. F. Aspinall was at the head of the party. As far back as 1888 the system had been applied, Fig. 4, to tank locomotives with four axles weighing 34 tons, running on the 1-metre (%foot 3.4-inch) gauge on one of the departmental railways in France, and in 1889 the “ Maffei” firm of Munich constructed four engines on four axles weighing GO tons (in running order) and one on six axles weighing 85 tons. These tank engines built for a normal gauge were intended : The first for the Swiss Central Railway and the second, Fig. 5, for the St. Gothard Railway. This second engine was then the heavies6 engine in the world-the United States excepted. In 1894, engines on four axles and separate tender weighing 56 tons were built for the railways of the Prussian State, Figs. 6 and 7 (pages 440-1). As can be seen the essential features do not differ materially from those of the first engine of 1887. Many similar engines were built for various German railwa,ys and for the Hungarian railways. In 1895 six-axle engines with separate tender were built by Messrs. Borsig of Berlin, and later by the PontiloE firm :tt St. Petersburg, for the %foot G-inch gauge of 850 kilometres (528 miles) from Vologda to Archangel, Fig. 8. It is interesting to note that it was not for flexibility that the system was adopted, since curves were not less than 350 metres (1,148.3 feet) radius, but it was for the light weight of rails, 18.5 kilograms per ‘metre

(37 * 3 lb. per yard). This meant that R large number of axles must be coupled together, so its to olritain the required tractive power. In 1898 another Rnssim line-the Moscow-Kazan hie-had engines built on six axles weighing 79 tons. One of these engines was exhibited at Vincennes at the time of the Universal Exhibition of 1900. A. great number of these have been built, and superheated steam has been applied to the most recent engines. The director of that important company, Mr. Noltein, said at the Railway Congress at 2K2

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FIG.7.--Prussian State, 1594.

F~ ......

..... I,,,,' ''~~~

FIG.8.-OsEaw-Vologd~-Arc~a~ge~, 3-joof 6-inch Gazrgc, 1995.

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Berne in 1910 that the is better than any other when it is desired to drive an engine of considerable weight over light rails. Under such circumstances it cannot be replaced by any other type with parallel axles. The example given by the Moscow-Kazan Railway ~vassoon followed by the Trans-Siberian Railway, to which the system was particularly suitable, given the lightness of the track : 24 kilograms per metre (48 lb. per yard) rails. Two type-models of these engines, one for passenger trains with four driving axles and a carrying axle in front weighing 56 tons in running order, and the other for goods trains with six driving axles weighing 81 tons, were built with

FIG.g.-Superlieatcd Steam Engiiae, Central AragopL Railtoay.

the intention of using them as patterns. These engines proved of great value during the Russo-Japanese war. Large tank-engines on six axles were built in 1902 by Borsig of Berlin for the cod traffic on the Chemin de fer Central d’Aragon. Gauge 1.676 metre (5 feet 6 inches). These locomotives weighed 108 tons in working order, and were the heaviest built at the time, except in the United States. This company uses many engines of the same type but with separate tenders weighing only 72 tons. Some of them, only recently built by Henschel at Cassel, are provided with Schmidt superheaters. As will be seen in Fig. 9 superheated steam comes from the smoke-box to the rear cylinders through two pipes placed outside the boiler. One

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JV1.Y 1913. COMPOUND ARTICULATED LOCOMOTIVES. 443 can see how easily superheated steam may be applied to this type of engine where its use is as simple :ts on ordinary engines. In conclusion, the author refers to the engines with six axles coupled with reparate tenders built in 1908 for the Chinese line from Pekin to Kalgan by the North British Locomotive Company of Glasgow, which are the first engines of this type built in Great Britain. They weigh 98 tons and pull trains on long 30 per cent. gradients round curves of 152 metres (499 feet) minimum radius. The author is glad to say that when he was revising this Paper he learnt that the firm of Maffei in Munich, the builders of the first normal gauge Mallet engine, had recently constructed a huge tank-engine of the same type, with eight axles coupled in two groups. The engine weighs 122.5 tons in running order, and is of course the heaviest locomotive in the world-the United States excepted. Table 1 (page 444) shows the principal dimensions of a few engines for narrow gauge, and Table 2 gives those for wide gauge. The first engine of this type was built in 1887, as already mentioned. In 1892 there were 110 of them in existence, and over 400 early in 1900. Since then the number has increased rapidly, and at present reaches about 2,500. They are to be seen in about fifty countries distributed all over the world, and belong to about 150 different railway companies or administrations, some owning but a few, whereas others have from 50 to 350. It was in 1904 however that the type made unexpected strides onwards. This was due to the following circumstances :- There was then in the United States a very pronounced tendency towards reducing the cost of transport of goods by means of very heavy trains, so that powerful engines were required. The power of an engine is limited by the space between extreme axles and the weight which the wheels carry to the rails. Moreover the following was unsatisfactory : On many sections the track was very severe so far as gradients and curves went. In 1902 the biggest American engine was an engine with five axles coupled and two carrying axles weighing 120 tons, of which 106 tons was adhesive weight. It could give a tractive force of 28 tons. This engine

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 TABLE 1. Showing a few Types qf Mallet Engines for Narrow Gauge.

South South Arics- African African Bone- La Pae 1.067metre. Iepartmenta Guelma 1*067 metre. 1.000 metre. :000metre. North- 1.ocN) metre. American Winterthur. Hanoverian British Locomotive Batignolles. Society. Locomotive Company. Company. I Number of axles . . . 0-3 + 3-0 1-2 + 3-0 0-3 + 3-0 0-3 + 3-0 0-3 + 3-0 1-3 + 3-0 1-3 + 3-0 Diameter of cylinders ins. 13.8-17.7 12.6-20.0 12.0-19.0 15.0-22.8 15.6-24.0 17.5-28.0 18.0-28.5 Piston stroke . . ins. 22 23 22 28 23 26 26 Diameter of wheels ins. 43 42 40 43 43 46 46 Distance between parallel' - 96 102 100 axles . . . . ins. 91 87 100 Total distance between' 272 291 401 492 extreme axles . ins. 257 326 252 Grate area . . . sq. ft. 20 29 16 16 30 43 50 Total heating surface 1092 1793 2616 3391 sq. ft. 1243 1744 926 Steam pressure in boiler 213 193 199 lbs. per sq. in. 171 171 199 199 Working weight . tons. 46.2 52.2 45.2 60.5 59.1 95.5 100.4 Adhesive weight . tons. 46.2 44.3 45.2 60.5 59.1 86.6 86.6 Weight of tender, full 23.G 37.9 tank engine tank engine 39.4 43.3 56.1 tons Total weight . . tons. 69.8 90.1 45.2 60.50 98.5 138.8 156.5 Tractive force-compound 10.9 16.7 18.0 tons 6.5 7.1 7.4 11.8

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Sltoicing n feui Types of Mallet Engines for Wide Gmigc.

Pebin- Prussian Hungarian Kalgan State Trans- hntral Aragon . .435 metre. Gothard State Siberian ;435 metre. 1.435 metre. L.435 metre. 1.676 metre. North- The :525 metre. Borsig. British Maffei. Alsacian Company's Kolomna. Society. Locomotive Workshops. Company.

Number of axles . . . . . 0-3 + 3-0 0-2 + 2-0 0-3 + 3-0 0-3 + 3-0 0-3 + 3-0 0-3 +- 3-0 Diameter of cylinders. . ins. 15.6-33.8 15.5-23'6 15.8-24.4 16 *7-28.0 18.5-28 0 16.0-28.5 Piston-stroke . . . . ins. 25 23 24 26 at 28 Diameter of wheels . . ins. 43 50 46 4G 43 51 Distance between parallel axles \ 103 69 106 102 118 116 ins. I Total distance between extreme 1 320 228 315 303 343 352 axles ...... ins. I Grate area . . . . . sq. ft. 24 21 24 39 37 45 Total heating surface . . sq. ft. 1669 1529 2530 2196 2369 2605 Steam pressure in boiler 1 171 218 171 171 236 lb. per sq. in. I 171 Working weight . . . tons 74.8-85 * 6 55.1 70.9 79.8 56'6-106.3 96.5 Adhesive weight . . . tons 74.8-85.6 55.1 70.9 79.8 86.6-106.3 96.5 Weight of tender, full . tons tank engine 39.4 - 44.3 tank engine - Total weight . . . . tons 74.8-65.6 94.5 - 121.1 86'6-106.3 - Tractive force-compound tons 9.9 94'5 10.3 124.8 15.3 17.7

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belonged to the Atchison, Topeka and Santu FB Railway, and was a compound tandem engine. For higher twctive forces three engines had occasionally to he coupled to one train. Tliis was :t costly, ungdinly and sometimes even a dangerous solution to the problem. The author had long come to the conclusion that the United States, with their wider loading gauge, their heavy weights per axle and their method of coupling, which made provision for an enormous tractive force, was just the ideal ground for the application of his system. He had entered into communication with an American firm, but without success. At last, in 1903, the American Locomotive Co. constructed for the Baltimore Ohio Railway :L Mnllet engine with six axles, weighing 152 tons (running order), i.e. 25-3 tons per axle, which was exhibited at St. Louis in 1904, Fig. 10. This engine was greatly criticized and several engineers agreed to look upon it as a model-which would probably remain unique- of a monstrous locomotive, difficult to handle for everyday traflic, and being serviceable only as a pusher on very broken lines or on lines of determined gradients. There was also a doubt as to the way the coupling of the two trucks and the movable tubing would behave in practice. When the engine started to run, after the Exhibition, it was found that those criticisms were based on nothing serious, and that the hopes of its success had not been exaggerated. Two years later, in 1906, the Bwldwin firm, which had already built a few similar engines for the narrow gauge of Porto Rico, delivered five engines to the Great Northern Railway, U.S.A., with six driving-axles and two carrying ones: one in front, the other

behind, weighing 162,000 kilograms (159 * 4 tons), of which 144,000 (141.7 tons) was adhesive weight, Fig. 11. These engines, like the first one, played the deof “pushers,” but the excellent results they gave prompted the company to use them for road service, that is, for pulling goods trains, and twenty-five similar engines, weighing 130,000 kilograms (128 tons), of which 113,000 (111.2 tons) wiis adhesive weight, were ordered. These engines pulled 1,300 tons at a speed of 16 kilometres (9.9 miles) per hour on a gradient as high

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I II ,--- L' :...&I

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a5 1 per cent., on which the “Consolidation” engines only took 1,000 tons, using the hnme amount of coal ; this meant a saving of 30 per cent. In 1907 a further step was taken in increasing the number of driving-axles when the “ Erie Rnilway ordered three

locomotives on eight axles, weighing 185,500 kilograms (1 73 * 7 tons) entirely for adherence. These engines were intended to haul trains of 3,000 tons over the 12 kilometres (7.5 miles) section on a gradient of 13 per cent. between Susquehanna and Golf Summit. This was done successfully, and a considerable saving in staff, coal and time was the result. From that time many American lines started using this new type. Another interesting fact to consider was that the introduction of the new engines, which were very powerful, caused the ordinary engines to be discarded. MY. George H. Emerson, of the Great Northern Railway, conceived the idea of combining his ‘‘ Consolidation ” engines, two by two, and turning them into Mallet engines with the introduction of new boilers. This transformation gxve good results, and locomotives of the Prairie type were treated in the same way. But the most remarkable transformation was that carried out by the Atchison, Topeka and Santa FB Railway using locomotives with 10 wheels coupled, already referred to. In 1902 they were the largest engines in the United States. The frames were utilized for the rear portion of the new engines, and the original low-pressure cylinders of 0.813 metre (9 feet 8.01 inches) diameter were fitted with inside liners so as to reduce the diameter to 0.711 metre (2 feet 4 inches) and transform them into high-pressure cylinders. A front truck was added, carrying the low-pressure cylinders of 0.965 metre (3 feet 2 inches) diameter, and a new boiler was fixed containing, owing to its length, a superheater, a steam rehenter going from one group of cylinders to the other, and :I reheater for the feed-water. These newly transformed engines scaled the enormous weight of 227,000 kilograms (223.4 tons), of which 200,000 (196.9 tons) was adhesive weight, distributed over ten axles.

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c

pU

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Shoii~in~~CL fcw Types of Mtcllet Engines in the Chited States.

(See Figs. 10-13, pages 44'7 and 449.)

Ealtimore- Baltimore- Erie Atchison, Ohio Great Ohio Virginia 1907. Railway Topeka and 1904. Northern American 1911. Santa FB American 1906. American - - Locomotive Locomotive Baldwin. Locomotive Baldwin. Company. Baldwin. Company. Company.

Number of axles . . . . . 0-3 + 3-0 1-3 + 3-1 0-4 + 4-0 0-4 + 4-0 1-4 + 4-1' 1-5 + 5-1 Diameter of cylinders . ins. 20-32 22-33 2:>-30 26-41 28-44 28-38 Piston stroke . . . . ins. 32 32 28 33 32 33 Diameter of wheels . ins. 56 55 51 56 56 57 Distance between parallei axles \ 120 120 168 1so 180 240 ins. j Total distance between extreme\ 368 535 470 487 478 797 axles ...... ins. J Grate area . . . . . sq. ft. 72 78 100 100 81 83 Total heating surface , . sq. ft. 5587 3907 53 18 5533 6923 3918 Steam pressure in boiler 1 228 213 213 213 213 228 lb. per sq. in. J Working weight . . . tons. 149.6 158'5 182.0 205.7 204.7 274.6 Adhesive weight . . tons. 149.6 140.7 182.0 205.7 184.6 245 Weight of tender, full. . tons. 62.9 65.9 73.8 80.7 78.8 101.4 Total weight . . . . tons. 212.5 224.4 255.8 286.4 283.5 376'0 Tractive force-compound tons. 26.5 28-5 36.4 44.3 43.3 49.2

~~ ~ ~~~

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The company has, besides, constructed others on the same model, heavier still, weighing 280,000 kilograms (275 * 6 tons), of which 250,000 (246 tons) is adhesive weight, and which give, when working compound, a tractive force of 50,000 kilograms (50 tons) at tread of wheels. Table 3 gives the main dimensions of some of these engines. It will be seen that for a few, the diameter of low-pressure cylinders is equal to, if not greater than, that of the boilers of sixty years ago. There are actually on American railways the following types of Mallet engines :-2-4-4-2, 4-4-6-2, 0-6-6-2, 2-6-6-2, 2-6-8-0, 0-8-8-0, 2-8-8-0, 2-8-8-2, 2-10-10-2. These engines are to be seen at the present day on some forty lines in the United States. They are used for various purposes, either on easy lines for very heavy trains or with less loads on severe gradients. According to American engineers the adoption of this system is justified by the following advantages :-- 1. Distribution of adhesive weight over a great number of coupled axles. 2. Diminution of weight on the wheels, reducing the deterioration of track and bridges. 3. Considerable distance between extreme axles and reduced distance between parallel axles. 4. Great flexibility of the engine, reducing the wear of rails and flange. 5. Advantages arising from the use of double expansion and superheated steam where economy is concerned. 6. Division of the mechanism into two sets. 7. Small relative weight of the parts of the mechanism and decrease in repairs. 8. Reduction in the repairs of the boiler as compared to those of the engine, owing to there being only one boiler for two engines. 9. Ease and simplicity of driving. To these advantages it may be added that the use of double

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expansion reduces the slipping of the wheels considerably. Articulated locomotives with double high - pressure cylinders, independent of one another, often give rise to difficulties in iwnning, due to the fact that when they are working at full pressure on an incline it is nearly impossible to make both cylinders give the same hauling power, and either the one or the other starts to slip. Trains frequently stop on severe gradients for that reason. Such is not the case wit.h articulated compound locomotives on account of the reliability of the two sets of cylinders working on the same steam. If the high-pressure group start to slip, the cylinders of that group exhaust their steam in the receiver quicker than the low-pressure cylinders can use it, and the pressure at the receiver as it goes up stops the slipping. In the same way if the wheels of the front group start to slip, the low-pressure cylinders discharge steam quicker than tlio high-pressure cylinders can feed them, and the pressure goes clowri at the receiver so that the wheels cease slipping. If slipping take place in both groups at tlie same time, action can be taken t~ccordinglyas with ordinary engines. The arrangement of articulated frames used by the author has been criticized. It means this advantage, however, as was pointed out in a pamphlet published by the Baldwin firm: so long ax the effort exercised by the driving connecting-rod on the crank- pin is not at a dead end, the pressure of steam tends to push the bottom of the cylinder :tnd the frame in opposite directions. In articulated engines this is according to an arc of a circle described with the axis of articulation as centre. If the pistons on both sides worked together the two actions would balance one another, but the crank-pins are placed at go", so that during one turn of the wheel there is a point when the pistons are moving in opposite directions, and twice in every revolution they are tending to turn their separate frames, first one way, then another. All engines have a certain amount of play, either between the rails and the flanges of the wheels, or in themselves, so that movement may take place laterally for an amount equal to the sum of these oscillations. But before this displacement is reached it is first of all

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counteracted by inertia, then by friction of the flanges against the rails, and by more friction like that of the journals in the axle-boxes, etc. The sum of these resistances multiplied by the radii z and y, Fig. 14, at the end of which the resistance takes place, represents the resistance of the engine against transverse displacement. This resistance is greater for the Mallet than for the Fairlie engine, on account of the greater length of the lever arm. In the two types the reaction on the crank-pin is tangential to an arc of a circle having for its radius c, the distance of the axis of articulation from the axis of the cylinder and the moment of rotation is the product

FIG.14.-Corpurutive Stability of the Fairlie and Mullet Engines, under the action of the pistons. Mallet.

of the reaction by this radius. From which it follows that the Mallet engine is more stable than the Fairlie; for with equal loads on the driving-wheels and the same distance between axles, it opposes a greater moment of resistance to the displacing factors. Lateral stability is a very important item, for if the moment is insufficient the engine will continually oscillate and bring about a rapid wear of the flanges and excessive play. This is opposed to safety, and in any case means very costly upkeep. A few engines of this type have been constructed with cylinders of equal capacity (all working at high pressure), The author does not advocate this scheme in which one is deprived of the advantages to be realized by the adoption of double expansion both for simplification of 2L

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piping and reduction in slipping. This system is only justified in the case of a loading gauge which does not allow the adoption of low-pressure cylinders of convenient diameter. The author believes he could not do better than conclude with an extract from a Paper read at the Franklin Institute on 16th January 1910 by Mr. Grafton Greenough :- lLWe find that wherever continuous heavy road service or heavy pushing service is required, the Mallet compound articulated locomotive has more than done what was expected of it. We also find it because of the articulated features adapted to lighter work where rigid base wheel engines are not practicable. In all heavy service, of a nature which enables an engine to work a considerable portion of its time to anything like maximum efficiency, we find that in addition to being more effective than other types of engines, the Mallet locomotive is by far the most economical design of locomotive yet devised. Without doubt its advent has eliminated the necessity -for a time at least-of widening the gauge of our railroads and has in many instances postponed the laying of additional tracks because of the reduction in the number of train movements it niakes possible. Furthermore the introduction of the Mallet type of locomotive has justified the retention of steam locomotives as motive power on economical grounds alone, where, in a number of instances, electricity generated by water-power bids fair to invade. “That the solution-for a time at least-of the apparently insurmountable difficulties attending the hauling of heavier trains, has been obtained with practically no change in roadways, is due primarily to the common-sense design of locomotive, developed by Mr. Anatole Mallet, seconded by the untiring energy and perseverance of the railroads officials, who in conjunction with the builders of locomotives had the temerity to give these engines a fair trial, and so mould their particular features to comply with modern railroad conditions that their efficiency is no longer an experiment but a positive accomplishment.” The author deems it his duty to bring forward the above opinion of American engineers to the notice of European railway

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JULY1914. COMPOUND ARTICULATED LOCOMOTIVES. 455 engineers and locomotive builders (the latter numbering about thirty), to whose initiative and ability the results which have been set forth in this Paper are greatly due.

The Paper is illustrated by 14 Figs. in the letterpress.

Discussion,. The CHAIRMAN(Mr. Michael Longridge, Vice-president), in proposing a hearty vote of thanks to the author for his Paper, said it dealt with a most interesting subject, espeoially to those who had to do with pioneer railways in foreign countries, where heavy gradients and short radius curves must necessarily be used on account of cost. It was many years since he had anything to do with locomotives, and he had not followed the developments of late years. In his locomotive days the Fairlie engine was the only practical articulated engine, and it was used with considerable success. It consisted to all intents and purposes of two locomotives coupled together, but considerable difficulty was experienced with the joints of the steam-pipes. He remembered designing an articulated locomotive for heavy goods traffic in which he coupled the by steel cog-wheels, The engine never got further than the design, but he thought there was something practical in it at low speeds. His attention was drawn to it through his experience on the Mont Cenis Railway, where the grades were 1 in 8 and the curves of 40 metres radius. The trains were limited in weight and length, because a wheel-base of only 8 feet 6 inches could be used, and consequently it was necessary to employ a locomotive of very short wheel-base. Locomotives with two cylinders and with four cylinders were tried, the latter having a very complicated motion, and it was found that for practical purposes the ordinary two- cylinder locomotive without any complicated motion was the best. 2L2

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Mr. EDQARWORTHINGTON (Secretary of the Institution) said it was very kind of the Chairman to ask him to step up from the Secretary’s chair in order to address the Meeting. It was the first time he had been asked to take part in a discussion at an Institution Meeting since becoming Secretary, although he had done SO at the Graduates’ Meetings, and he much appreciated the honour. He desired to take this opportunity of saying that engineers owed much to the author in the development of modern locomotives, not only for improving the articulated type, but also for the large amount of pioneer work carried out in teaching the world how to work locomotives by double expansion. It might be known to some members that for twenty-three years before becoming Secretary of the Institution he was a locomotive constructor, and he desired to say a few words with regxrd to the author during that period. From 1876 every one looked to M. Mallet, and the results he was obtaining in the South of France, to learn if it were worth while spending money on further experiments to develop the compound locomotive. At Crewe in 1878 the late Mr. Webb was quick to see the advantages that M. Mallet had obtained, and he (Mr. Worthington) had the duty and pleasure of experimenting on many of the details for the application of the Mallet intercepting valve to an old Trevithick engine which had worked on the Lancaster and Carlisle Railway from its earliest days, and subsequently on other types of locomotive. The former was partially successful, but being a single-wheel engine with small cylinders it could not haul much load. That led to Mr. Webb’s development of the three-cylinder engine, the third or 1.p. cylinder being placed below the smoke-box, and driving an independent pair of wheels. From 1880 to 1885 Mr. Worsdell and Mr. von Borries followed M. Mallet, making improvements in the intercepting valve, and the system was used largely in England, Germany and South America. There was no development of the Mallet system in North America for many years, although a four-cylinder compound engine worked on the Boston and Albany Railroad in 1883, and proved a precursor of the four-cylinder engines

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JULY 1914. COMPOUND ARTICULATED LOCOMOTIVES. 457 introduced on the Chemin de fer du Nord in 1886; but Mr. Sandiford took the question up at, Lahore in India with great success, and subsequently read a Paper * before the Institution giving details of the work he had accomplished. With regard to the articulated locomotive which M. Mallet had now brought before them, Fairlie engines were worked on the narrow-gauge Blaenau-Festiniog Railway in North Wales for many years previous to the time to which he was referring; and on the last visit of the Institution to Paris in 1889, he believed also in 1878, several articulated locomotives were at work on the Decauville Railways. M. Mallet had kept to the articulated type and developed it, in spite of many difficulties experienced by himself and other people. In the early days, the difficulties were mainly in the steam-pipe, which was made with a ball-joint to carry steam to the cylinders, but the design had more recently been so much improved that he understood those troubles had vanished. Many engineers had tried to make substitutes for the Mallet articulated locomotive. Some of these were successful in a way, but others were not, particularly in the case of the powerful twin engines designed and built for the railway from the Indus Valley up the mountains and through the Kojak Tunnel. On that railway the grades were very heavy and the loads were great, so one big tender was made with an engine at each end, and thus the railway was worked for some time. After the engines had been running for a year or two, he visited India in connexion with other work, and took the opportunity of going up to the Kojak Tunnel for the purpose of seeing the twin engines working. He found that some more tenders had been built, and the engines had been paired off with them. Throughout all the attempts to build an adhesion locomotive of enormous power, with as little weight as possible, the author’s articulated engine seemed to have come out on the top in the end ; and the fact that huge Mallet engines were now working the very heavy trains in the United States was a proof that they

* Proceedings, I.Mech.E., 1886, page 355.

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 458 COMPOUND ARTICULATED LOCOMOTIVES. JULY1914. (Mr. Edgar Worthington.) were still successful. He thanked the members for allowing him to join in this discussion.

Dr. H. S. HELE-SUAW(Member of Council) said it might interest the members to know something about a successful development of articulation that had recently occurred, in which not steam, but oil under pressure, was conveyed from the locomotive itself to the under-carriage in order to articulate wheels. The oil- transmission system was making rapid progress owing to the development of the internal-combustion engine. It was absolutely necessary witk such a prime mover to have some means of imparting to the work to be done that flexibility which could not otherwise be obtained by anything but a steam-engine. It might not be known that in the development of rail-cars the necessity was being felt very much indeed of some form of transmission to impart such flexibility. It was a very diacult thing, es all engineers knew, to convey to the portion constantly working on the road or rail fluid under high pressure through a joint, when that joint was always in active operation. Two successful applications of the principle had been made on two rail-cars of more than 100 h.p., one of which was being sent to Canada and the other to South Africa. These cars were not much more than in the trial stage, and he would therefore not say anything further about the matter, except that the very same trouble of articulation which had always presented a great difficulty to builders had now, as far as could be seen, been overcome for oil-transmission gear.

Mr. F. H. LIVENSsaid that, without feeling at all competent to discuss the question which had been placed before the members, he thought there was one point on which others besides himself would like further information. The development in the size of the locomotive had necessarily increased the size of the boiler and of the fire-grate. In Professeur Snuvage’sPaper reference was made to the difficulty of firing wide grates, and a preference was expressed in favour of the narrower grate. He noticed in Table 3 (page 450) of M. Nallet’s Paper that some fire-grates were shown having an area

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JULY 1914. COMPOUND ARTICULATED LOCOMOTIVES. 459 of from 72 to 100 square feet. The largest grates referred to in Professeur Sauvage's Paper were somewhere about 40 or 50 square feet in area. If difficulty was experienced in firing the ordinary fire-grate, it would be interesting to know how it was proposed to overcomc the difficulties that must occur when still larger grates were used ; for instance, how many fire-doors and how many firemen were employed. No clue was given as to the amount of coal which had to be shovelled in per hour, and he thought the members would agree that, while provision was being made for increasing the adhesive power of the locomotive and the size of the engine end, it would be useful to know what provision was made for surmounting the difficulty in dealing with the increased size of the heat-producing part of the system.

Mr. G. W. A. GREENsaid he had just returned from Chile, where, on the Nitrate Railways, quite a large number of Fairlie locomotives were used, and he thought it would be of interest to the members present to hear something of their performance. The railway line was, like most of the lines in that part of the world, full of curves and very heavy gradients. He believed the ruling gradient was 3 per cent. ; what the least radius of the curves was he could not say. The practical men who were out there working on the line told him that the most successful locomotive was the Fairlie, and some of those locomotives had been running since 1864. He believed the latest one was built in the shops in Chile in 1911. No Mallet locomotives were used. The locomotives, other than the Fairlie type, all had a fixed wheel-base with not more than six wheels coupled. One trouble experienced with the Fairlie engines was that there was no place available to put the fuel. Briquettes were largely burnt, and if coal was used it was put in sacks. When the locomotive was at work, it was a common thing to see the roof of the cab and both ends of the boiler piled up with sacks of coal, because there was nowhere else to put them. As far as he knew, those locomotives pulled heavier trains and gave less trouble than any other type of engine on the line. He had never heard of any trouble with the articulated joint, although

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 460 COMPOUND ARTICULATED LOCOMOTIVES. JULY 1914. (Mr. G. W. A. Green.) it was quite possible that some had been experienced. One Shay locomotive had been tried on the line. This locomotive had a vertical engine beside the boiler, and transmission to the driving wheels was by a shaft with universal joints and bevel wheels ; but he believed it was quite a failure. An American engineer was sent out with it to erect it. It was taken once up the heaviest section of the line about 25 miles in length, with a climb of about 3,000 feet to the main junction at the higher level, and it successfully pulled an enormous train up at about 4 miles an hour. When it went down again an ordinary nitrate bin of about a dozen cars, with 30 tons of nitrate on each, was attached, and the brakesmen proceeded to let it down at the usual rate of 20 to 30 miles an hour. As a result the gearing on the Shay locomotive could not keep up at all, and the locomotive had to skid the whole way down from top to bottom. After that experience it was not run again.

M. ANATOLEMALLET, having explained the working of a model exhibited, thanked the members for their kind remarks concerning him. He did not think it was necessary for him to reply to the different remarks of the members, and would close by thanking the Institution, not only for their having very kindly thought of asking him to write a Paper, but also for the extremely hearty welcome they had given him.

Comnzunications.

Mr. E. L. AHRONSwrote that the Mallet engine had a much greater lateral stability than engines of the Fairlie type, and this appeared to the writer to be best shown by a consideration of the resisting moments of inertia. In the Fairlie engine the centre of oscillation was close to the centre of gravity of the oscillating steam-, and the amplitude of oscillation (8) at unit distance

Downloaded from pme.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 JULY1914. COMPOUND ARTICULATED LOCOMOTIVES. 461 from the centre of oscillation would be (neglecting effect of obliquity of connecting-rods) :- in which W is the weight of the unbalanced portion of the reciprocating masses for one cylinder ; c is the distance from centre line of truck to centre line of cylinder; r L: crank radius; TL2 is the moment of inertia of the bogie, in which L is the radius of gyration and T is the weight of cylinders, frames, and motion (with all attachments) which rested upon the journals, that is, the weight of the mass which oscillated. If, as in the Mallet engine, the pin or centre of oscillation were moved back, through a distance I, to a point behind the bogie, the moment of inertia would become TL2 + TP, 1.414 Wcr and s = ____ T (LZ + 12)' The units throughout may be feet and pounds, or metres and kilograms. The writer had no detailed weights, but concluded from an inspection of the diagrams given, that 12 is roughly from 12 to 15 times L2, so that the effect of moving back the king-pins had been to produce a verylarge increase in the denominator of the expression, and thus greatly to reduce the value of s. It was to be observed that in the case of both bogies of the Fairlie engines and the leading (1.p.) bogie of the Mallet engine, both T and L2 were comparatively small, as the oscillating mass did not include the boiler, etc. Moreover, s would be still further increased, because W-the reciprocating mass-for the low-pressure bogies was large. The 1.p. pistons in the case of some of the U.S.A. engines varied from 38 inches to 44 inches diameter. It would be extremely interesting if the author would be kind enough to add some particulars of the weights of unbalanced reciprocating masses on the one hand, and of the oscillating masses of the steam-bogies on the other hand, and to give some further information as to the methods adopted for balancing these engines.

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Mr. W. M. URIEwrote that the author made lithle reference to the Meyer type of articulated locomotive used on the Luxembourg Railway, built by the Compagnie Belge in Bruxelles in 1873 and shown at the Vienna Exhibition. Mr. Kitson was the locomotive superintendent at that date on the Luxembourg Railway, and he elected to try the Meyer type against the Fairlie type, with a view to simplifying the generation of steam. The engine was a four-cylinder one with twin bogies and was most successful. The writer had made out most of the detail drawings under the immediate direction of Mr. William Paterson, formerly chief draughtsman on the London, Brighton and South Coast Railway, and of MY. Meyer. It must be a great satisfaction to M. Mallet to see the success of his invention.

[me Author, oioing to circumstances beyond his control, was unable to send in an9 written Reply before the Proceedings went to press.- SECRETARY,I .MEcH.E.~

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