62 



NATURE 



[May 15, 1890 



The type of compound locomotives first used in any 

 number is that patented by Mr. F. W. Webb, the able 

 Mechanical Superintendent of the London and North- 

 Western Railway. This design is interesting because it 

 is to a certain extent an example of really original work 

 in locomotive practice. Mr. Webb had several very good 

 ideas to work on in this design, all of very great import- 

 ance from an engineer's point of view. These ideas were 

 as follows : — The engine must not have a double throw 

 crank-axle, this being certainly the weak point of all 

 inside-cyhnder engines ; the coupling rods between 

 driving and trailing wheels must be done away with, 

 since these also sometimes break, and may cause serious 

 accidents. The doing away with the coupling rods 

 enables a longer fire-box to be used, because the coupled 

 wheels should be near together to obtain a minimum 

 length of coupling rod, for reasons of safety. Thus, to 

 design an engine to be more powerful than an ordinary 

 four-coupled express of the North- Western heavy pattern, 

 and having at the same time fewer parts liable to accident, 

 as stated above, requires some clever scheming and much 

 thought. The engine ultimately adopted by Mr. Webb for 

 use on the London and North-Western Railway has three 

 cylinders, viz. two high-pressure cylinders and one low- 

 pressure cylinder. The high-pressure cylinders are placed 

 one on each side of the engine, and are connected to the 

 trailing or hind pair of wheels. The low-pressure cylinder 

 is placed between the frames at the front end of the 

 engine, and is connected with the front pair of driving 

 wheels by a single-throw crank-axle. It will be noticed 

 that in this arrangement each pair of wheels are driving 

 wheels, that the side or coupling rods are done away 

 with, and that the ordinary double-throw crank-axle has 

 given place to a single-throw crank-axle, which may 

 be made of ample dimensions and practically unbreak- 

 able. The course of the steam through the cylinders is 

 easily understood : steam passes from the boiler to each 

 high-pressure cylinder, and, after doing a certain amount 

 of work, it is led from each high-pressure cylinder into 

 the steam-chest of the low-pressure cylinder ; it is there 

 expanded down to a still lower pressure, and then exhausted 

 finally up the chimney. 



The cylinders of the Dreadnought type — that is, the 

 most powerful type of the compounds on the London and 

 North- Western Railway— are: high-pressure cylinders, 

 14 inches in diameter and 24 inches stroke ; the low- 

 pressure cylinder has a diameter of 30 inches and 24 

 inches stroke. These engines are designed in such a 

 manner that, when working at their usual speed, the 

 power developed by the high-pressure cylinders, and 

 applied through the hind pair of wheels, shall be about 

 equal to the power of the low-pressure cylinder, and 

 applied to the front pair of driving wheels. 



Through the kindness of Mr. Webb I am able to give 

 an account of the working of a special train, run in order 

 to test the fueJ and water consumption of this class of 

 engine. 



On April 17, 1887, the engine Dreadnought, No. 503, 

 worked a special train of coaches and dynamometer car 

 from Crewe to Wolverton, a distance of 105I miles, at a 

 speed of 24 miles per hour, including stoppages, which 

 were made every 15 miles on the journey ; 24 cwt. of coal 

 were put into the fire-box during the trip, which gives a 

 consumption of 25*4 lbs. of coal per mile ; 2629 gallons of 

 water were evaporated, which equals 978 lbs. of water per 

 pound of coal consumed. The weight of the train, ex- 

 clusive of engine and tender, was 259 tons, 3 cwts. 3 qrs , 

 and the mean weight of engine and tender 62 tons 13 

 cwts., or a total of 321 tons 16 cwts. 3 qrs. for the whole 

 train. This is equivalent to 4-13 tons of train hauled to 

 I ton of engine and tender hauling it, and vib oz. of 

 coal per ton per mile. 



The same locomotive worked a similar train between 

 the same points on January i, 1888, but at a speed of 44 



miles per hour, with one stoppage only at Rugby, the 

 results being as follows : — 30 cwts. of coal were put into 

 the fire-box during the trip, which gives a consumption of 

 4r3 lbs. of coal per mile; 3608 gallons of water were 

 evaporated, which equals 8"26 lbs. of water per pound of 

 coal consumed. The weight of the train, exclusive of 

 engine and tender, was 256 tons, 18 cwts., and the mean 

 weight of the engine and tender 62 tons 13 cwts., or a 

 total of 319 tons li cwts. for the whole train. This is 

 equivalent to 4'i tons hauled to i ton of engine and 

 tender hauling it, and 2'c6 oz. of coal per ton per mile. 



When the first trip was made, the weather was warm 

 and dry, but during the latter a hard frost prevailed. 

 With this exception the conditions under which the trips 

 were made were practically alike. The difference in 

 fuel consumption between the two trips may be taken as 

 that due to the difference in speed. There are 'j'] com- 

 pound locomotives now at work on the London and North- 

 western Railway, which have run to the end of December 

 1889 a total of 13,423,798 miles, and several more of the 

 same type are now being built at Crewe Works^ 



It will be observed that in the Webb type of compound 

 locomotive the design is such that the sizes of the 

 cylinders can be easily increased if necessary to obtain a 

 still more powerful engine, provided, of course, a larger 

 boiler is used, and there is no reason why even the 

 Dreadnought should not be the forerunner of still more 

 powerful compounds on the London and North- Western 

 Railway when their use becomes a necessity. It is 

 evident that the use of a third cylinder, with motion and 

 gear, must entail a greater cost for repairs as well as a 

 larger consumption of oil when at work, and that the type 

 of engine does not easily lend itself to a speedy and 

 economical rebuild of ordinary locomotives to the Webb 

 compound type ; the system, therefore, is one quite 

 unique in its way, and unlike any of the eariier attempts 

 at compounding locomotives. 



Another successful design of compound locomotives is 

 that due to Mr. T. W. Worsdell, the Locomotive 

 Engineer of the North-Eastern Railway, on which rail- 

 way a large number of compound locomotives are at 

 work. The Worsdell compound is the outcome of many 

 experiments both at home and abroad. There are two 

 cylinders used, and to all appearances the locomotives 

 are similar to the ordinary non-compound locomotive. 

 These two cyhnders are of different diameters, and the 

 steam, after doing work in the smaller one, is exhausted 

 into the steam-chest of the larger or low-pressure cylinder, 

 where it is further reduced in pressure by expansion in 

 the cylinder, and afterwards is exhausted. It will be ob- 

 served that in the Webb system there are two high- 

 pressure cylinders connected to the hind pair, of wheels, 

 with the crank-pins, of course, at right angles, and that 

 the low-pressure piston receives no steam from the high- 

 pressure cylinders until the engine has commenced to 

 move. Thus, all the work of starting the train for the 

 first few revolutions of the driving wheels has to be done 

 by the high-pressure pistons, and these are always able to 

 start, in whatever position the wheels may be, because 

 they are in duplicate and have no dead point. In the 

 Worsdell system this is not possible without some 

 special appliance, and it is this particular appliance 

 which constitutes the patented device in the engine 

 which makes it the success it is. In any two cylin- 

 dered compound engine with cranks at right angles, 

 which is the usual practice, it is possible to easily observe 

 that there are two positions from which the engine cannot 

 start on the admission of steam, because the admission of 

 steam to the low-pressure cylinder depends on the exhaust 

 from the high-pressure cylinder, and the high-pressure 

 piston may happen to be at exactly the end of its stroke, 

 either at the front or the back end— known as being on 

 the centre or dead points. As the Worsdell engine is 

 constructed with two cylinders, as before stated, it will be 



