Proceedings Institution of Mechanical Engineers:
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Volume 119 (1930)
Pendred, Loughnan St. L.
Random reflections: Address by the President. 943-54.
"What I have been endeavouring to do is to stir up a spirit of courage and adventure amongst our members. All around us we see new methods springing up and the infallibility of old laws and old beliefs being challenged. Something should come out of it all, and I hope our own young British engineers and scientists will give rein to their thoughk, and the spur to their activities." Quotations from Kipling and Robert Louis Stevenson!
Volume 120 (January to June 1931)
Unveiling of Replica of Tablet affixed to George
Stephenson's Cottage at Wylam-on-Tyne on 20 February 1931. 249-51.
Unveiled in the Institution's Headquarters by Richard W. Allen. The original bronze tablet had been affixed to the exterior of Stephenson's cottage in June 1929. The commission for the plaque had been given to Professor Maryon, of Durham University, which Sir Archibald Ross undertook to cast in his own foundry.
High-pressure locomotives. 101-35. Disc.:135-206 + 3 folding plates. 8 illus., 14 diagrs., 2 tables, 2 plans.
In his paper on "High-Pressure Locomotives," read on Friday evening, January 23, before the Institution of Mechanical Engineers, Mr. H. N. Gresley, chief mechanical engineer of the L. & N.E. Ry., described some special features of considerable interest relative to the water-tube boiler of the high-pressure engine No. 10,000, which was completed to his designs at the end of 1929 at the Darlington Works. To prevent the formation of scale in the tubes of the boiler, so far as possible, arrangements were incorporated to heat the feed water, so that its temperature when delivered into the water chamber was over 400°F. or only about 50° less than that of the saturated steam in the boiler. Much of the scale and mud was thus thrown down in the forward portion of the top drum of the boiler, and after running over 15,000 miles only a slight deposit of hard scale was found on the inner rows of tubes in the firebox. Any economy in maintenance would become fully apparent after the engine had been running for a few years.
It had been ascertained that the cost of a water-tube boiler, similar to that fitted to No. 10,000, would not be appreciably greater than that of the wide firebox pattern as fitted to L. &N.E. Ry. "Pacific" locomotives. The most expensive details of the water-tube boilerthe solid forged steam and water drums-were not subjected to the action of the fire, and consequently might be expected to have a long life.
When stationed at Gateshead the locomotive worked express trains from York to Edinburgh and back, involving a daily run of about 420 miles. Whilst other engines of the "Pacific" type in the same link require washing out after running 1,000 to 1,500 miles, this engine ran 5,000 miles without washing out, and when opened up it was found that the boiler was exceptionally clean and the tubes in good condition. The superheater elements of the boiler of No. 10,000 are located in the forward portion of the central flue, and are subject to radiant heat. In order to prevent the flame impinging directly on the ends of the elements, a brick column is provided in the centre of the main flue immediately in front of the brick arch. Notwithstanding this precaution, and owing to the fact that there were no data available as to the effect of radiant heat on superheater elements, the temperature to which steam was superheated during the preliminary trials was excessive, temperatures of 900°F. being obtained; consequently the lengths and area of the superheater elements have been reduced, so that a temperature of approximately 700°F. can now be obtained, and this is regarded as sufficient. The superheater elements are situated between the boiler and the regulator and are, therefore, always subject to full boiler pressure. In order to prevent overheating when the regulator is closed, the steam supplied for auxiliary services is taken from the superheater and passes through a coil of ribbed pipes laid in the feedwater chamber, thus raising further the temperature of the boiler feed and at the same time de-superheating the steam. This de-superheated steam is led to the reducing valve where its pressure is reduced to 200 lb. per sq. in. Steam from this reducing valve supplies a manifold pipe on the footplate across the front of the boiler above the firehole door. From this manifold pipe steam at 200 lb. per 'sq. in. pressure is taken for supplying all the auxiliary services, such as the injector, vacuum ejectors, and steam brake, reversing gear, steam sanding, steam heating, whistle, and turbo-generator. It has been possible to retain the standard steam fittings for this purpose. Only the safety valves, regulators, and water gauges have had to be made to suit the working pressure of 450 lb. per sq. In.
The heating surface figures are now as under:-
Firebox 919 ft2.
Combustion chamber 195 ft2.
Small tubes 872 ft2..
Total evaporative 1,986 ft2.
Number of elements 12
Diameter. inside 1.18 in.
Heating surface 140 ft2.. .
Total heating surface 2,126 ft2..
Having only two sets of valve gear, it was regarded as necessary to be able to vary the cut-off of the high-pressure cylinder independently of that of the low-pressure cylinder, and only by trial at varying cut-offs could the best results be realised. Therefore the rocking link by which the high-pressure valve is actuated, is so arranged that provision is made by means of a slot and die-block to varv the travel of the valve, at the same time retaining" the combination lever to keep the lead constant. The reversal of the low-pressure valve-gear, and consequently of the whole engine, is actuated by the ordinary form of steam reverser, and a similar equipment is provided to vary the high-pressure cut-off. Both these equipments are attached to the shafts they actuate, and being so remote from the footplate their delicate control was not easy. This has been successfully effected by the use of telemotors; another telemotor is also provided for operating cylinder cocks.
As built, the engine had two high-pressure cylinders 12 in. in diameter and two low-pressure cylinders, each 20 in. in diameter, all cylinders having 26 in. stroke. It has been found that by reducing the diameter of the high-pressure cylinders to 10 in. a more equal distribution of work between the high-pressure and low-pressure cylinders results.
In his paper, Mr. Gresley described in some detail the notable high-pressure locomotives which have been built by the American Locomotive Co. to the designs of Mr. J. E. Muhlfeld for the Delaware & Hudson Railroad: the Schmidt-Henschel three-cylinder compound locomotives, built by Henschel & Sons for the German State Rys., as well as the Paris, Lyons & Mediterranean Ry., and by the North British Locomotive Co. for the L.M. & S. Ry., the Winterthur high-pressure tank locomotive built by the Swiss Locomotive & Machine Co. to the designs of Mr. Buchli, and the Schwartzkopff-Loftier three-cylinder locomotive, built by the Berlin . Machine Works to the order of the German State Rys.
In opening the discussion on Mr. Gresley's paper, the President said they had listened to an admirable paper from a chief mechanical engineer who had produced an engine that might be considered with pride as an "all British" production. As so many were desirous of discussing the paper, and the discussion would probably have to be adjourned, he invited those who had come from a long distance to speak first. Mr. Scarth, of Yarrow & Co. Ltd., said that although the boiler of No. 10,000 departed somewhat from the usual Yarrow form, an outstanding feature of the type had been retained in the small number of riveted joints, and further, the water tubes could be readily inspected internally, while ashes and coke could be easily removed. He thought higher working pressures could be considered for future locomotives. Some interesting remarks on the performances of the Schmidt-Henschel and Loftier locomotives were made by Mr. Wempe of the Schmidt Superheating Co. of Cassel, and he was followed by M. Hoffner of the French State Rys., and M. Rogers of the P.L.M. Sir Henry Fowler then gave some of his experiences on the high-pressure locomotive of the Delaware and Hudson RR As the President suggested that a boiler-designer should give his views, he called on Sir John Thornycroft to make a few comments. This gentleman gave Mr. Gresley great credit for the way in which he had succeeded in depositing the hardness of the water in the form of sludge, which could be blown out. Good water circulation was of the utmost importance if the generating tubes were to be kept in order, and he wondered, when the boiler was working very hard, if the proportions of the heating surface were such as to give the circulation required. Mr. R E. L. Maunsell in his remarks, said he hoped later on that Mr. Gresley would give details of the cost of maintenance, running costs, etc. Referring to the arrangements made at the front end for keeping the steam clear of the cab windows, he mentioned the success of the "blinker" plates used on the Southern Ry. Mr W. A. Stanier spoke of the Delaware & Hudson RR locomotives which he had had an opportunity of seeing, and the troubles they had had with too many tubes in the firebox. Lieut.-Col. E. Kitson-Clark confined his remarks to questions as to the mechanical details of No. 10,000. He wished for more particulars of the bogie arrangement under the firebox, and further asked where the tail rods for the highpressure cylinders were. He also referred to the ratio between the diameters of the high-pressure and the low-pressure cylinders, and to the method adopted for varying the cut-off in the high-pressure cylinders. At the resumed discussion on the 7th inst., when replying, Mr. Gresley showed a very ingenious electrical device for ascertaining if any scale is present in the water tubes, glowing lamps being extinguished whenever the working end of the instrument, pushed down a tube, encountered scale. The above is based directly on the brief summary which which appeared in Loco. Rly Carr. Wagon Rev., 1931, 37, 38-9.
Locomotives described include the Delaware & Hudson two-cylinder compound locomotive of 1924; the Schmidt-Henschel three-cylinder compound locomotive of 1926; the Swiss Winterthur high-pressure locomotive (2-6-2T) of 1927; and the Berlin Machine Works Schwartzkopff-Löffler three-cylinder locomotive of 1930. He then described No. 10000, with its Yarrow boiler. Discussion: N.H. Scarth (Yarrow) (Pp 135-6); F. Wempe (Schmidt)(136-7); G. Haffner (Chief Engineer, French State Railways p. 137); A.C. Roger (French State Railways p. 137-8); Sir Henry Fowler (138-9) who commented on other high pressure locomotives, on the oil separator on the Löffler boiler, and on the chimney and smoke deflectors fitted to No. 10000; R.E.L. Maunsell (p. 140) commented on smoke deflection; W.A. Stanier (pp 140-1) supposed that since the days of the Brotan firebox, locomotive engineers had thought that they would like to try water-tube fireboxes or water-tube boilers. It had been left to the Author to show them that not only a watertube firebox but a complete water-tube boiler was possible for a locomotive. He had had the opportunity of seeing the Delaware and Hudson Railway engine with a water-tube firebox, and he had gathered from Edmonds, the chief mechanical engineer of the railway, that the trouble with the first engine which had been built had been due to tubes of too small diameter in the firebox, and that he had subsequently enlarged the diameter of the tubes with advantage. He asked if the Author had found that the outer tubes in his boiler received any appreciable amount of radiant heat from the fire.
There was little to criticize in the Paper under discussion unless one had had experience with the type of boiler with which the Author was experimenting. He hesitated, therefore, to express any opinion of the boiler other than that it seemed to be a sound mechanical design. He would, however, like to ask the Author whether he had considered, in proportioning his cylinders, reducing the low-pressure cylinders to 18 inches diameter rather than the high-pressure to 10 inches diameter. He also wished to ask whether the ordinary means of lubrication with a pressure lubricator were satisfactory with high-pressure steam.
E. Kitson Clark (141): commented on the ratio betwen the hp and lp cylinders and cited E.W. Selby J. Instn Loco Engrs Paper 257.
H.A. Stenning (p. 142-4) Stenning said that regarded from the point of view of economy, it seemed that the chief object of the designers of the high-pressure locomotives which had been described had been to eliminate the expense of the ordinary type of firebox and its maintenance. No high-pressure locomotives had been running for any length of time. Apart from the American type, there was only the multi-pressure boiler of the Schmidt type to judge of in service, and that only over a very limited period. He was not satisfied that it was a long enough time to enable one to draw conclusions, but it was known that at the end of three years of more or less continuous service the water-tubes of the closed circuit had been examined and found to be as good as when they had been installed. He had pieces of the tubes which had been examined in his possession and they showed no deterioration either inside or outside. If, however, circulation in water-tube boilers or a water-tube circuit was at all inefficient, all sorts of troubles would occur. He had encountered some of them in the Schmidt-Henschel engine built at the North British Locomotive Company's works in this country. Excessive temperature combined with excessive pressure had set up stresses which were more serious in their effects than those due to pressure alone. For modern high-pressure boilers new materials had to be used and he was sure that the Author would admit that the choice of a suitable material for the drum to keep it within permissible limits of weight had been a problem. The use of special steel which was necessary tended to make the construction costly, and it was more important to know whether the increased capital cost was balanced by the reduction in the maintenance costs of the firebox than to ascertain how many pounds of coal the engine burned per ton-mile. Coal was a comparatively small factor and what was required to be known was the total cost of drawing a ton load for a given distance.
He had doubts as to which of the two-cylinder high-pressure, or the three-cylinder or four-cylinder compound engines, was the best arrangement. In England the three-cylinder engine was used. Again, the proper degree of superheat to use was a question which had been raised for many years. In the early stages of superheating 100° F. of superheat was considered ample. To-day 250° to 300° F. of superheat was customary, and one might well consider whether a pressure of 450 psi was necessary, or whether still higher pressures would be advantageous. There was probably some happy mean between the highest and lowest both of pressure and temperature, but what it was he would not like to say. Nevertheless, the answer governed the problem of balancing capital cost and maintenance upon which the ultimate economy rested. The Author had mentioned that one of the tubes in his locomotive became overheated at one point. Could he give some indication of the degree of heat to which it was subjected, and the exact location of the tube Z He assumed the Author had employed a fire-door of the automatic type. That was most important in high-pressure locomotives, because if anythmg went wrong the whole of the contents would be blown out through the fire-hole pretty quickly at a pressure of 450 psi. In the closed circuit of the locomotive Fury built for the London, Midland and Scottish Railway, there were 120 gallons of water, and, as he himself was unfortunately aware, on an explosion taking place in this closed circuit, the whole of this was blown out in about three seconds. He asked if the Author had considered what would have happened to the fire-bars as a result of using preheated air. If they were found to deteriorate more quickly than in the normal firebox, he suggested that they should be treated with aluminium.
He noticed that the blower pipe had been carried along so as to clean the tubes near the centre of the boiler, but he did not think it was carried down to the bottom of the firebox near the corners where it was rather important to place it so as to clear the ashes from the bottom of the water-tubes in the firebox itself. In most of the engines described, the steam-drum was protected by cross water-tubes underneath the bottom surface, or at any rate the drums had been taken out of the line of the fire. In the Authors engine, the steam-drum was immediately above the brick arch, and he was not at all sure that it would not get burnt. The designers of the Schmidt-Henschel engine adopted protective means, for their steam-drum was in exactly the same position. The effect of the flame or gases of combustion circling round the end of the brick arch was very severe and it seemed to him that there was a blow-pipe action directly on the surface above it. He asked whether the large smokebox had any appreciable effect on the exhaust, pressure in the cylinders. He assumed that the baffles for circulating the gases were now placed in such a position that no excessiv; temperature occurred in the superheater. The difficulty of excessive superheat had also been mitigated by moving the superheater further to the front of the engine.
He thought these locomotive experiments were the most interesting events occurring on British railways. The railway companies had broken away from their traditional conservatism and were now actually carrying out more experiments here than in any other country of the world. Three such experiments were in progress-the Authors, the Schmidt-Henschel locomotive for the London, Midland and Scottish Railway, and the pulverized-fuel locomotive on the Southern Railway-all aiming to draw tons more cheaply within the allowable limits of weight and gauge. He felt sure that as a result, the locomotive would still maintain its position as the cheapest tractor the world had ever seen.
Ernst Gysel (144-5) referred to the soluble deposits of scale in the portion of the boiler which was most intensely heated by the fire. A thin layer of such hard scale was found in the tubes surrounding the firebox in the Winterthur high-pressure locomotive after some 25,000 miles of service. It was pcssible to remove this scale completely and no tubes had to be taken out of the boiler, but naturally the matter had been intensively discussed between the responsible engineers of the firm with a view to deciding whether there was any danger due to such deposits, and whether the use of natural water in boilers of the type built, for instance, by Mr. Gresley or that built by the Swiss Locomotive Works was subject to certain limitations. He would like to have Mr. Gresleys opinion on that question. He would like to say that the figures of steam and coal consumption which Mr. Gresley had mentioned in connexion with the Winterthur locomotive had been carefully measured and checked by railway officials in Switzerland, when the locomotive was subjected to tests on the Czeczott principle, and when making use of the dynamometer car which was attached to the locomotive. There was no doubt that with high pressures of steam, a coal consumption of less than 24 lb. per d.h.p.-hr. could be obtained (the best figures had been 1.9 to 2 lb.), and this enabled the designer to build engines of a reasonable size with greater power than had hitherto been possible. The locomotive built by the Author was of the type 4-6-4, and he was wondering whether criticism he had heard from certain quarters, that that type of locomotive might sometimes be deficient in adhesion weight, was justifiable. Did it happen in service, say when running at high speed, that too much load was supported on the leading and trailing axles and that, in consequence, the driving axles became unloaded and the locomotive had a tendency to slip ? He was personally of the opinion that that criticism was not justified, as means could always be provided to secure an even distribution of the load, but it would be interesting to hear how the Authors engine had behaved in service with regard to that point.adhesion charcteristics of 4-6-4;
W.W. Marriner (Yarrow, pp 145-7) said he was sorry he could not carry out the wish of the President and give an opinion as to the value of higher pressures for locomotives, but he could say that in marine work during the last five years pressures had increased by one-half. A pressure of 400 Ib. per sq. in. was quite common to-day, and, if it was safe to prophesy, 600 lb. per sq. in. might in two years be quite usual. A recent list had shown a number of enormous land boilers which had been made in the United States, all of them having an evaporation of over 200,000 Ib. of water per hour, and all having pressures of over 1,000 lb. per sq. in. Those high pressures were being used in conjunction with turbines, and since one understood that it was at the lower end of the pressure range that the steam-turbine had the advantage in efficiency, and that a reciprocating engine had the advantage at the higher end, in he thought that high pressures for locomotives were very likely to be a thing of the future. When the Author had invited Mr. Yarrow to co-operate with him in the design of his locomotive boiler, Mr. Yarrow had been very pleased to accept, and he could assure them that all Mr. Yarrows staff had a1so been delighted. It was surprising how much they had learned by their association with the Author and his staff. The members had no idea of the difficulties there were in getting such a powerful machine into such a small space, and within the limits of the permissible weight. They had even learned a great deal about boiler-making itself. It had been mentioned that the bottom of the steam-drum was directly exposed to flame. For that reason the bottom of the drum was made thinner, a practice which his firm had adopted for many years for very much higher rates of evaporation than occurred even in the Authors locomotive. It was done in order that the transmission of heat might not be impeded by thick metal, and not the least trouble was experienced in consequence. When his firm had been called in some time ago by the American Locomotive Company to assist them with the designs of a high-pressure locomotive boiler, they had not gone as far as they had done in this case. The Americans, however, had enormous advantages, which they had not realized then, in their very much larger loading-gauge and less severe weight restrictions. From the experience gained in connexion with the locomotive under discussion, he had no doubt that if locomotive engineers were going to use high pressures extensively it would be necessary to adopt an all-water-tube boiler, and not to have stayed surfaces, He might add that Mr. Gresleys boiler would have been a much simpler problem if there had been another foot of headroom. Col. Kitson Clark had pointed out the bold step which Mr. Gresley had taken in putting the trailing driving axle in front of the firebox. That had helped them considepbly. It would, in fact, have been extremely difficult for his firm had not Mr. Gresley been able to propose that way of getting out of a serious difficulty. Sir John Thornycroft, as one might expect, had put his finger right on the central difficulty in designing a locomotive water-tube boiler. The first thing one had to choose was whether to have considerable complexity of design, or simplicity but with provision for cleaning the tubes. There was no doubt at all that the Author had adopted the correct solution. With regard to the temporary hardness, everything possible had been done in order that the water entering the steaming part of the boiler was as pure as possible. It would be seen that the feed-water was introduced into the front end of the drum where there were no tubes. Inside the drum there was a Gresley injector. In an ordinary injector the steam drew the water, but in this injector the water drew the steam. Consequently the water was heated practically to the temperature of the steam in the boiler. As a result the temporary hardness of the water was deposited on the forward side of the weir in the drum. With regard to the permanent hardness of the water, it was surprising that their knowledge of chemistry had not enabled them to deal with it in any way except by letting it deposit and subsequently scraping it off. When using hard water a very good indication as to the circulation was given by the appearance of the inside of the tubes, and when using coal a very good indication was given by the deposit on the outside of the tubes as to whether they had been hotter than usual. In the Author's boiler they had been more than satisfied with regard to the circulation. Whether or not that was due to Mr. Gresley insisting on his firm putting in tubes almost twice as big as they had wanted to he would not like to say, but there was no doubt it was successful. What they now knew about circulation made one wonder what on earth happened in a locomotive boiler of the type they used to install in destroyers-very large boilers with narrow water spaces, which burned best Welsh coal at the rate of 90 lb. per sq. ft. of grate. As to the future, there was not the least difficulty in making a boiler similar to that of locomotive No. 10,000 for any pressure that might be required. The system of air-heating which had been adopted in the Yarrow-Gresley boiler was so efficient that the loss from radiation which might be feared with high pressure and temperature was very small indeed, and it was quite independent of the temperature of the boiler itself. It was possible that the next step would be to stoke the boiler by mechanical means, especially for very large sizes, but at present in this country one man was quite able to do the work.;
Charles King (147-9) queried the efficiency of 18% claimed for the Löffler boiler; P.J. Cowan (149-52) mentioned improvements in boiler feed; that Horatio Allen suffered from leaky seams and stated that wheel arrangement of 10000 was really 4-6-2-2; W. Gregson (153-5) discussed problems of hard water with the Brotan firebox and queried "how did No. 10,000 compare with the 250 lb per sq in in four-cylinder simple engines of the G.W.R. which had always been noted for their economical running" (Gresley did not respond!);
E.L. Diamond (154-6) remarked that one admired the Authors locomotive, not only as an ingenious product of the engineers skill, but most of all because the designer had brought to his problem a broad sense of proportion, so that this engine might be regarded as the culmination of a series of designs and developments which had had as their object not the production of a spectacular test figure, but the conferring of a real commercial gain to the railway operating department. In that connexion, it was surprising that no reference was made in the Paper to the Baldwin compound locomotive with a boiler pressure of 350 psi which was so fully discussed by Mr. Lawford Fry in his paper before the Institution in 1927. That locomotive also was a sound, practical development, and not merely a freak experiment having little relation to the actual facts of locomotive operation.
The Author had said early in his Paper that designers of locomotives were only following the lead set by the designers of large stationary plants and marine engines. One had sometimes thought that that had been true too literally ; high pressures had become a fashion, and the locomotive engineer had felt he must have his highpressure engine too. And so they had had the somewhat anomalous position of tentative and risky experiments with enormously high pressures whilst more than half their standard locomotives offered a comparable possibility of economy by the elimination of valve leakage and a reduction of their low-pressure limit by 5 or 10 psi, an economy which merely required the redesign of their valve-gear according to the best modern practice.
For what were the facts? The theoretical utmost gain in efficiency which could be obtained in a locomotive by increasing its pressure from 250 psi to 450 psi. was about 20%, corresponding to an increase in the Rankine cycle efficiency from 18½ to 22½%. That assumed roughly the same superheat temperature in both cases, about which he would have more to say in a moment, and a back pressure of 17psi. absolute. But how many locomotives exhausted against a back pressure of 17psi. at their normal running speed ? Still a minority he feared. It was not always realized that whilst it was possible to obtain an indicator diagram showing a low back-pressure line from almost any locomotive, that line would show a far less favourable state of affairs at high speed, and an exhaust pressure at 25 psi absolute was much nearer the figure actually appropriate in most cases. The reduction of that pressure by 8 psioffered a gain of over 10%, or fully half that attainable by an increase of boiler pressure by 200 psi. Only those who had had extensive footplate experience knew how seldom a locomotive ran with the regulator fully open. Indeed, thousands of locomotives scarcely ever had their regulators fully opened, and he had often wondered what was the good of maintaining a boiler at a pressure of even 200 psi when the steam in the cylinder never exceeded 150 psi. or so. Much of the locomotives work was done at a mere fraction of its total power output, and that would considerably reduce the saving in coal that could be expected from the highpressure locomotive in service. Confirmation of the importance of those considerations would be found by studying published results of locomotive tests. The coal consumption of standard passenger locomotives had been reduced from over 4 lb. per d.h.p.-hr. to 3 lb. per d.h.p.-hr. simply by equipping them with modern long-travel piston- or poppet-valves. The further reduction claimed for even the very high-pressure locomotives was only to 2½ lb, and those claims were not yet fully substantiated. Whilst they still had so many 4 Ib. per d.h.p.-hr. locomotives running about, it was obvious which was the first method of reducing that coal bill of £12,000,000. The question of the lower limit of pressure, was, moreover, one that became increasingly acute as the upper limit was raised. A locomotive which had a boiler pressure of 450 psi. required the steam to be expanded to six times its original volume (making allowance for the clearance steam) as compared with the three-anda- half times necessary for a locomotive having a pressure of 250 psi, if the same back pressure was to be maintained. In other words, if more careful attention was not given to valve-gear and cylinder port design in the high-pressure locomotive, most of the gain of efficiency accruing by adding 200 psi. at the upper end of the scale would be lost by adding a few pounds per square inch
But this was not all. at the lower end ! The urgency of that consideration was emphasized by the fact that some difficulty had been experienced in securing adequate expansion of the steam in recent locomotives pressed to 250 lb. per aq. in., and it had even happened in individual cases that an improvement in coal consumption had been effected by reducing the steam pressure at the regulator valve.
The Author was probably well enough aware of those considerations ; compounding in itself was not sufficient to secure adequate expansion of the steam, and one turned with the deepest interest to the table of dimensions on page 120 to find that the Author had given exceptional length of travel to his valves, and to the cylinder drawing on page 132 to find that admirably short, straight, and wide ports had been included in the design. Another factor which should not be passed over was the influence of superheat temperature. Was it sufficient that steam at 450 Ib. per sq. in. should be superheated to about the same temperature as steam at 250 psi in locomotive practice, or were locomotive engineers soon going to follow the stationary plant designers and hanker after temperatures of 1,000° F. ? The Author said that a temperature of approximately 700" 3'. was considered sufficient, and he hoped he would allow no one to shake him in that belief, at any rate until he contemplated adding a condenser to his equipment. It was of course true that with increase of pressure increase of temperature was necessary to maintain the same dryness fraction in the steam' at exhaust. But who was certain that the steam of a modern superheater locomotive had any moisture in it at all at the end of expansion in the cylinder when running at normal speed ? He had failed to find any experimental evidence on this point, and an investigation that he had made some time ago * suggested that at a high speed the degree of superheat was so much increased by throttling at admission that the steam was still above saturation point at the moment of release in the cylinder. If that were so, it would be absolutely futile to enter the hazardous region of high steam temperatures so long as the steam-locomotive remained, by the necessity of its circumstances, so much more rough-and-ready an affair than the power generating steam-plant.
R.J. Glinn (156-8) spoke about mobile power stations equipped with water tube boilers used during WW1 (illus. page 159).
Gresley in response on page 162 noted that some questions had been raised with regard to the construction of the back of the engine. There had been no room to put in a bogie because it would be seen that the ashpan was placed very low. The trailing axle was really a Bissel truck with Cartazzi slides for centralizing. The axle in front of it was interchangeable with that used on the Pacific engines. It was a peculiar arrangement, and it had to be adopted because of the circumstance he had mentioned. The result, however, was that the engine was very easy riding. There was always the possibility with a 4-6-4 type engine of getting a symmetrical arrangement, resulting in the setting up of a swaying movement. A dissimilar side control at the leading end from that at the trailing end tended to break the synchronization. Certainly the engine described had no tendency to set up a periodic side sway. As to whether it was a 4-6-4 or a 4-6-2-2, he should certainly describe it as a 4-6-4. He imagined that 4-6-2-2 would be the correct designation of an engine having a bogie in front, followed by six wheels coupled, a booster on the next axle, and a pair of carrying wheels behind.
Gresley in response on page 164 Major Gregson had referred to the magnesium limestone content of the water in the district through which the engine No. 10,000 would have to work, and reference had also been made by another speaker as to the desirability of softening the water. Probably the deposit in the inner tubes of the engine was due to magnesium limestone; it had been very hard. On the question of watersoftening generally, not only for the engine under discussion, but for all the existing engines, he was firmly of opinion that if the water in England could be treated ao as to be similar to that which was available in Scotland, the expenditure on the water-softening plants would be repaid in a comparatively short time by the lower cost of maintenance of locomotive fireboxes. In Scotland engines were running their full time between general repairs with practically no dirt in the boiler. One of the new Pacific engines of the L.N.E.R. was stationed in the Edinburgh district, and ran between Edinburgh and Glasgow and Edinburgh and Berwick, and also to Newcastle. After running 90,000 miles it had come into the works for general repair. He was at the works at the time, and he had himself examined the firebox. It looked perfect, and not a single stay had to be renewed. If that engine had been running in England south of the Tweed, 200 or 300 stays would probably have had to be renewed after running that mileage. The total life of a firebox in Scotland was a great deal longer than that of a firebox in England.
The paper was discussed in Manchester on 5 February and the following contributed: H.L. Guy (165-7);
Captain H.P.M. Beames (166-7) said it afforded him very great pleasure to pay tribute to his old friend, the Author, and he was sure that every one who had watched the progress of locomotive No. 10,000 would have been impressed with the courage and resourcefulness shown in its design. Moreover, to those who, like himself, had to maintain boilers of the Stephenson type, the successful attempt which the Author had made to eliminate large flat stayed surfaces promised future relief from a great deal of trouble. Indeed, the presence of those surfaces had been one of the reasons which had restricted the advance of pressure in locomotives hitherto. He wondered, incidentally, what trade was supposed to deal with the building and maintenance of a boiler of that type. He could foresee some lively controversy between the fitter, the boiler-maker, and the tuber ! On looking at the diagram of the locomotive, it would appear that the centre of gravity was pitched rather high and that the engine might be unsteady, but he understood that at high speeds it was a particularly steady-running machine. It might also be supposed from the diagram that as a result of the free passage through the boiler given to the flue-gases the smokebox temperature might be rather high. He asked what this temperature was, and mentioned that in an engine of the " Royal Scot " type a smokebox temperature of 650' F. was attained under certain conditions. Could the Author also say how much water per pound of fuel was evaporated ? He inquired, further, whether any trouble was experienced in keeping up the refractory walls between the flues and the surrounding air chamber, and whether any trouble was experienced due to evaporation.
One of the difficulties with the ordinary type of superheater boiler was that the superheater was confined in flue tubes which frequently became blocked with cinders. In the type of locomotive they were now discussing, however, that trouble could not occur, but he nevertheless supposed that a certain amount of ash passed through the superheater, and he asked what means were adopted to clean it. Another point which would appeal to engineers was that the feed-water in the Author's locomotive was fed to the boiler by injectors, and it was not necessary therefore to incorporate a complicated system of pumps as in some of the other locomotives which had been described. In view, however, of the very high velocity with which the feed-water had to pass through the injectors he wondered if there might not be some trouble due to erosion of the cones.
He had asked that question in America when he had seen the first of the high-pressure What kind of piston packing was used? locomotives, and he had been assured that the packing in the locomotive at that time, after about six months running, was the original packing fitted in the engine. The packing and lubrication, indeed, had been so satisfactory that no alteration had been required.. He saw that a special form of regulator was used in the Authors engine. Was it a multiple-valve regulator, and did it give any trouble due to the high pressure of the steam ? Finally, he asked how the engine-drivers and the fwemen reacted to the higher pressure, for he well remembered the time when an old driver had handed in his resignation because the boiler pressure of his locomotive was increased from 6 to 12 Ib. per sq. in.
J.N. Gresham (167) referred to an article (Railway Engineer, 1931, 52, page 65). in which the thermodynamics and economy of high-pressure locomotives were studied, and the interest on additional capital cost plus probable increase in cost of maintenance were plotted against possible thermal economy. Unfortunately, the figures were presented on the basis of the cost of German coal, which needed to be rectified to meet English conditions, but it was stated that an increase in maintenance costs of £276 per annum would be likely to absorb 14 per cent in coal economy, and an increase in capital cost of £1,500 would require 7 per cent saving in coal to pay for itself. Looking at some of the high-pressure locomotives described in the Paper, they were bound to form the opinion that the capital cost of such locomotives must be such as to necessitate an enormous saving of coal to justify them. The Author, however, had stated definitely that in the case of his own locomotive the capital cost would not be materially increased and they could see for themselves that the number of auxiliaries was very much less than in the case of the other designs, and the general arrangement such as one would anticipate a small reduction in maintenance cost. A study of the article to which he had referred would convince them of the wisdom of the course Mr. Gresley had taken. He asked if the Author could give them any idea of the air pressure under the ashpan after the air had passed through the passages around the boiler shell
R.C. Bond (167) mentioned he had recently riden on one of the German Schmidt-Henschel high-pressure locomotives and of seeing the Schwartzkopff-Loffler engine, and he had been struck by the complication of those machines. The Schmidt-Henschel locomotive, however, did its work very satisfactorily, and appeared to require very little additional attention on the part of the engine crew. The only added responsibility was the maintenance of two water levels in place of one, which, under certain conditions, might be difficult. He thought that what was so very satisfactory about Gresleys locomotive No. 10,000 was its essentially British simplicity, and whilst, as the Author had said, a number of years would have to elapse before any definite results could be obtained in regard to actual savings, he thought there was not much doubt that the maintenance cost of the locomotive should be very little, if any, more than in normal circumstances. He would have liked to have seen some indicator diagrams and to have had particulars of the performance of the engine measured in drawbar horse-power output. The locomotive was interesting not only as a high-pressure locomotive fitted with a water-tube boiler, but also as a high-pressure compound. With one notable exception, the L.M.S. standard three-cylinder compound, compound locomotives had not been a success in this country. In his opinion the L.M.S. engines owed their outstanding success primarily to the simplicity of their design and to the fact that there was very little possibility of their being handled other than was intended by the designer. He felt, therefore, that the time would come when the Author would find it desirable to combine the control of the high and low-pressure cut-offs on one reversing lever. Although a welltrained driver might be able to arrange the cut-offs to the best advantage under varying working conditions, in many instances men had their own personal ideas, which did not always lead to efficient results. He inquired whether it had been necessary to fit non-return valves connecting the low-pressure steam-chests with the ends of the high-pressure cylinders in order to place them in equilibrium when starting away from rest on the low-pressure cylinders. The reduction in diameter of the high-pressure cylinders from 12 inches to 10 inches altered the ratio of the high- and low-pressure cylinder volumes from 1 to 2.77 to 1 to 4, and that in itself called for comment. The Author had stated that he had found it necessary to redistribute the work between the high- and low-pressure cylinders, but he wondered whether that could not have been done merely by altering the cut-off in the high-pressure cylinders relative to that in the low-pressure cylinders. With the reduction of high-pressure cylinder volume it appeared to him that it would be possible either to increase or decrease the proportion of work done in the highpressure cylinders according to the relation of the cut-offs in the two cylinders. He would like to know, therefore, whether it was desired to increase or decrease the work done in the high-pressure cylinders and also what were the cylinder clearances and the receiver volume, since both would have a considerable effect on indicator diagrams. The high-pressure cylinder had a 34-inch piston-rod but no tail-rod. With so small a cylinder that would give a difference of roughly 12 per cent in the forces on each side of the piston, and he thought it might have been desirable to provide a tail-rod. In examining the design of the boiler, a point which struck him was that the brickwork round the grate was somewhat shallow- If the engine were working with a fairly thick fire at the back of the firebox there might be some risk of burning coal coming into contact with the tubes, and be thought, therefore, that it might be desirable to carry the brickwork slightly higher, Captain Beames had referred to the accumulation of unburned fuel. Normally it deposited in the smokebox and was removed at the end of a run. He wondered, in the case of locomotive No. l0,000, not only how it was removed, but exactly where it accumulated. The Author had pointed out that in the operation of any water-tube boiler, prevention of scale formation was of the first importance ; if scale was kept out of the boiler it must obviously be deposited somewhere else, perhaps in the feed-water heater, and he would be interested to know how frequently the latter had to receive attention. He did not know whether it was generally appreciated that the washing-out of boilers cost a very large sum. On one of the British railways over 3,000 boilers were washed out each week, which resulted in each locomotive being out of service for any time up to sixteen hours. If all locomotives could be fitted with boilers which would run 5,000 miles instead of 1,500 miles between washing out, the saving would be very considerable. The Author had mentioned an evaporation figure of 20,000 lb. per hour on a four-hour basis. He asked if that was the maximum rate of evaporation of which the boiler was capable when working a heavy train. Considering the Author's standard 4-6-2 express passenger locomotives, working at 180 lb. per sq. in. boiler pressure, which would probably he capable of developing 1,500 indicated horsepower for long periods, and assuming a steam; S. Jackson (170-2); D.W. Sanford (LMS p. 172); C.H. Browne (on scale p. 172); E.F. Lang (on the relatively low boiler pressure p. 173) and Gresley responded (pp. 173-6).
The paper was discussed in Leeds on 12 February: speakers included F.C. Lea (177-8); E. Kitson Clark (178); W.T. Athey (178-9) stated that he had entered Gateshead as an apprentice in 1887, commented on compounding and boiler scale; R. Alan Thwaites (179) observed that the engine was in no sense a freak and he imagined that it was likely to be the forerunner of many similar ones, though some of the Continental engines described in the Paper might not survive. There was something very British about engine No. 10,000 both from the point of view of mechanical design and appearance. He thought that the only serious problem in operation was likely to be the water supply. The Author had adopted ingenious steps which largely but not entirely prevented the deposition of scale in the tubes, but it was interesting to note his view that if high-pressure locomotives came into general use it would probably be found economical to treat the feed-water. With this he entirely agreed, but he would go even further and suggest that it might be necessary to de-aerate it. In power-station practice where high-pressure boilers were employed it was necessary to eliminate from the feed-water both scale-forming solids in solution and oxygen. If oxygen were present severe pitting was liable to take place in the top drums at abont water-level. Boiler feed-water for an express locomotive was handled in such a way as to aerate it almost to the point of saturation. If, however, the water in the tender was kept under a partial vacuum, much of the oxygen might be removed. A thin deposit of scale would of course greatly reduce corrosion, but if in the future the water was so treated that no scale resulted, then serious consideration would have to be given to this question of the oxygen conten; A.W. Chapman (179 on scale); J.J. Sheridan (179-80); John Blundell (180-1); G.A. Musgrave (181) noted his own involvement in the design of the boiler between 1924 and 1930 when the locomotive entered service. Gresley replied on pages 181-3.
The paper was discussed at a meeting in Glasgow on 18 March: speakers included: Harold E. Yarrow (183-4); A.L. Mellanby (184-5);
David C. Urie (185) suggested that the boiler was the main point of interest at the moment to locomotive engineers. He took it that the Authors object had been to design a high-pressure locomotive boiler which should not greatly exceed in initial and maintenance costs a modern locomotive boiler of standard type. Realizing that, he had faced the fact that he must use raw water for boiler feed, and it was interesting to note the measures which were being adopted to precipitate as much of the solid matter as possible before the water entered the boiler tubes. Subsequent experience in this direction would be watched with interest by all locomotive engineers. He saw no future for a high-pressure locomotive unless its costs were not in excess of normal locomotives built for similar duties, because additional capital charges would quickly absorb the coal saving under normal working conditions as distinct from selected trials. He did not expect that the saving under such conditions could be much more than 10%. It had been mentioned by the Author that roughly 1 ton of coal had been saved in 8 on the round trip from London to Edinburgh. This was roughly 12½% and if 60,000 miles was the average annual mileage 150 tons of coal might be saved per annum. This did not leave much room for additional capital cost. He very much welcomed the remarks of Professor Mellanby in connexion with the high pressures which were the fashion or had been the fashion until lately. Indeed, he would say of some of the locomotives which had been described that they were not before their time but after it. He thought, personally, that the direction in which the Author was going was the one which was most likely to be fruitful in its results. He had no doubt that if additional locomotives of the type were built the cost of subsequent boilers would be considerably less than that of the pioneer boiler, and he noticed that the Author mentioned that the cost of this boiler should be very little in excess of that of the standard locomotive boiler used in his Pacific locomotives. He fully agreed that to increase the pressure from 450 to 900 or 1,200 lb. per sq. in. would add very little to the gain in thermal efficiency, but might add considerably to the maintenance costs.
Lindsay Foster (186-7) said that he was by no means clear as to the mechanism of the heat transmission between the closed circuit in the Schmidt-Henschel system and the steam evaporating drum. He presumed that the closed circuit was merely a means of carrying the heat from the fire to the high-pressure boiler in order to keep away from the hottest surface of the locomotive the crude water that was used in service. It appeared from the diagram that there was a good deal of space in the air-preheating passage in the Authors locomotive. Unless that space was necessary for reducing the resistance to the passage of the air he thought the air would be considerably more heated if it were restricted to a minimum so as to increase the velocity and ensure turbulence.; Robert Fox (187); J.M. Harper (188); Leonard Hyde (188-9);
George Ness (189) who chaired the meeting wondered whether water-tube boilers might not prove advantageous for locomotives other than main-line engines: experience with shunting locomotives for colliery sidings had shown that as the boiler pressures had been increased, the life of the fiebox was reduced. Whereas, some years ago, for colliery and contractors purposes one could reckon on a life of from ten to twelve years for a firebox, they were now not at all surprised to find it more or less worn out in four years. This generally depended on the curves and the gradient of the bank on which the locomotives were operated. He asked what was the life of the average locomotive firebox for railway purposes, and whether it had appreciably shortened in recent years. One thing quite evident from the high-pressure boiler described in Mr. Gresleys Paper was the magnificent engineering skill displayed by its design and construction. It was entirely different from the old type of boiler, and he thought especially that they could not praise too highly those who had forged the drums, and in such short time effected so great a reduction in their price.
T.E.H. Heywood (190) replying on behalf of Gresley said that he was very much surprised to hear that fireboxes of shunting locomotives in collieries were only lasting four years. The fireboxes of similar locomotives on the L.N.E.R. would last ten or twelve years, though, of course, he did not mean that they would not require any repairs during that time. In the event of any abuse with regard to leaky tubes, it might even be necessary to put in a new tube-plate or portion of a tube-plate. Undoubtedly it was of primary importance in connexion with the firebox of a locomotive that the stays and tubes should be kept tight. Experienced boiler-makers had said that if leaks in the firebox were attended to without delay and washing out was done properly, the firebox would last for the life of the locomotive. Shunting up gradients produced uneven expansion in the firebox and intensified stay and tube trouble, but he could not understand any colliery company in that district, with its good water, having undue trouble.
The adoption of the water-tube boiler for existing engines was a matter which had still to be considered, and it could not be decided until further trials had been made. Trials of the use of pulverized fuel for locomotives had been carried out in this country, but he did not think that even Messrs. Yarrow would go the length of saying that the use of pulverized fuel was an established practice in marine work. It was much easier to use pulverized fuel for marine or stationary work than in a locomotive. The cost of the Authors locomotive and its maintenance, and in fact the economic side of the whole experiment, could not be stated yet. The engine was experimental, and one could not base the capital cost of a highpressure locomotive on what this engine had cost. He hoped a representative of Messrs. Yarrow would answer the questions about the boiler. The work in regard to the rivets, drums, etc., was altogether different from ordinary locomotive boiler practice ; and he and his colleagues had learned a great deal from the work which had been executed by Messrs. Yarrow.
T.S. Finlayson (192) asked what variation was permissible in the high-pressure cut-off when the low-pressure cut-off was set at 60%. The centre of gravity of the locomotive was behind the centre of the coupled wheel-base which was inherent in the design, and he thought that might cause a tendency to produce lateral movement at the front end when running at high speed. The laminated springs on the bogie and coupled wheels were comparatively short, hence the deflexions were small and might produce harshness in running. One of the trailing trucks had a long laminated spring while the other had coil springs, giving deflexions greater than those of the coupled and bogie springs. It might be that in time the rear springs would settle down and the weight on the coupled wheels increase.
Problems of railway mechanics. 648-59. 2 diagrs.
Theoretical paper: from the point of view of analytical mechanics a railway train is a system of rigid bodies connected partly by rigid and partly by elastic bonds. As a rule, motion of this system is not uniform: the forces of inertia of all the parts of a train need to be take into consideration. These can be divided into two sections: those having progressive motion only along the track and those having rotary motion as well. For the latter, namely the wheels, the permanent way is a non-preventative obstacle. If this obstacle and all bonds between the separate parts of a train were rigid the solution of the problems of railway mechanics would be rather easy.
Woolltscroft, G.W. The training of an engineer.705-12.
The London, Midland and Scottish Railway in Derby had three grades of apprenticeship:
(1) Trade apprentices usually destined to become craftsmen.
(2) Priivileged apprentices, usually with secondary or public school training, who have to pass an entrance examination. These apprentices generally commence in the works at a later age than the former, and are allowed two mornings per w-eek, with pay, to attend a part-time engineering course at the Derby Technical College.
(3) The highest form of apprenticeship, namely pupils who had usually obtained an engineering degree, and who have a still more varied workshop training than the former.
Volume 121 (1931)
Locomotive experimental stations. 23-39 Disc.: 40-53. illus., 6 diagrs.
Described and illustrated earlier or existing plants: The Chicago & North Western Railway opened one in 1895, Columbus University initiated one in 1899, the Pennsylvania Railway installed one at the St. Louis exhibition in 1904 (this employed Alden brakes), the Swindon test plant opened in 1905, the German State Railways opened a plant with Froude water brakes at Grunewald in 1931 and a plant was under construction at Vitry-sur-Seine. Gresley noted that a locomotive testing plant arranged on the lines outlined by the Author embodies many features of an essentially novel character, and there is much detail work still to be done before the scheme can be regarded as complete. On the other hand, it is claimed that such a plant offers considerable advantages:
(1) The provision of a wind tunnel in which a locomotive can be tested.
(2) The arrangement of coupling the supporting wheels by means of bevelled gears directly to the longitudinal shafts produces conditions which approximate more closely to normal running conditions. Under normal running conditions a locomotive progresses along a fixed rail. Therefore a fixed locomotive should drive something resembling x caterpillar track, and the nearest workable mechanical arrangement to this is a set of supporting wheels rigidly coupled together. This eliminates the possibility of slipping on one of the supporting wheels, and the proportion of the power transmitted through the coupling rods is approximately the same as that which is obtained under running conditions.
(3) With the braking equipment concentrated in one place, fixed on rigid foundations, and away from the supporting wheels, the brakes are more accessible and can be more readily adjusted, and the use of flexible pipes, which is necessary if the brakes are directly coupled to the supporting wheels, is obviated.
In conclusion the Author submits that the provision of a British Locomotive Experimental Station is more essential now than at any other time. On the Continent and in America large sums of money are being expended upon the scientific development of locomotives, and these countries are obtaining orders in markets which were formerly wholly British. To meet this competition, and to provide for this country locomotives of the highest efficiency, it is necessary that we should have equipment second to none for the investigation of locomotive economy.
Very extensive abstract in Locomotive Mag., 1931, 37, 258-61 which includes some of the diagrams, notes presented in Cambridge and fails to record discussion.
Contributors to the discussion included G.V. Lomonossoff (40-2);
Stanier (42-3) commented on the Churchward plant and improvements made to reproduce actual running conditions on the plant and to power absorption: "perhaps the only one present who had had experience of a locomotive testing plant installed in this country, he could confirm all that Professor Lomonossoff had said about the difficulty of securing uniform results at constant speed. The locomotive testing plant at Swindon had certainly served a useful purpose, but it had to be remembered that locomotives were required to work on railway lines and it was impossible to reproduce in a testing plant service conditions. One of the principal requirements of Mr. Churchward, who had installed the plant at Swindon, was that a locomotive should be capable of maintaining a drawbar pull of over 2 tons at a speed of 70 miles per hour. Mr. Churchward had been quite unable to fulfil that requirement on the testing plant, but locomotives of the type tested had amply fulfilled that requirement on a level stretch of line between Bristol and Taunton when tested by means of a, dynamometer car. It had very soon been found that the testing plant at Swindon had inadequate capacity to absorb the power obtainable from a modern locomotive. There were also other difficulties in connexion with the plant. Most locomotive plants had at some time or other given trouble in the shaft bearings. It was indeed quite difficult enough to absorb the power of an individual axle, so far as his experience went, but in the plant suggested by the Author the power was carried first from the wheels to the shaft and thence to the brakes and dynamos at right-angles by means of bevel-gearing, and it did seem to him that this was to seek unnecessary trouble.
In view of the possibility of increase in the use of electric traction which was now looming ahead, he thought that it should be further considered whether a testing plant was still justified.
C.H. Bulleid (University of Nottingham p. 43) noted that the effect of the variable conditions on the road had been brought home to him very vividly many years ago when he had tried to compare two loconiotives by plotting curves for each showing the connexion between horse-power and speed. He had secured a large number of diagrams from two totally different engines, but when he had plotted the average curves he had found they were almost identical. He then realized that he had not been studying the locomotives at all ; he had been studying the train and the schedule to which it was being run ! He felt that a testing plant such as the Author had foreshadowed would be as important to engineers as the Froude tank was to naval architects.
C.H. Kuhne (pp 43-5) spoke about the Froude water dynamometer used to test road vehicles; T.R. Cave-Browne-Cave (page 45) spoke about wind tunnels; F.C. Lea (46).
Kitson Clark, E.
Humanity under the hammer [Presidential Address]. 107-41.
History of the hammer and hammering.
The manufacture and use of steel railway sleepers, 315-77.
Included Round-hole loose-jaw type (Indian State Railways); Webb's Pattern: Rafarel's Patent Sleeper (1887)
Some factors affecting the riding of coaching stock. 465-504. Disc.: 505-21. 25 illus & diagrs.
D. Raymond Carpmeal (505-6) spoke about the GWR use of the Hallade recorder; R.F. McKay on latex foam seating; A.N. Moon (508-14) spoke about the riding qualities of six-wheel bogies, tyre wear, overhang and portable accelerometers supplied by the Cambridge Instrument Co.; S.R.M. Porter (514) on the transverse velocity of the bogie frame relative to the bolster; A.S. Quartermaine (GWR, 514-15) on newly laid rail. G.H. Sheffield (515-18): the Pullman bogie was introduced to England by Sir James Allport of the MR.
Volume 122 (1932)
The mechanism of electric locomotives. 51-106. Disc.: 106-54. 36 figs.
Nose-and-axle suspended motors. the expected improvement in the rate of wear of track and of tyres was not realized by the substitution of locomotives of this description for normal steam-locomotives. It was found that the wear of flanges and of the rails on curves was reduced when the bogie trucks were connected by a hinged joint, capable of transmitting shearing forces, the wheel-base then being conveniently described as Bo + Bo. The tendency of each truck to nose outwardly produces a reaction on the hinge pin and slews the wheel treads across the rails, without heavy pressure on the flanges. Axle-mounted armatures: the gearless motor, having the armature mounted directly on the axle, was adopted by the New York Central Railroad for working main-line trains over the electrified lines connected with the Grand Central Terminus in New York. The first group of engines had the 1.Do.1 wheel arrangement, but the single-axle pony trucks as originally fitted were replaced by four-wheel bogie trucks, after the occurrence of a disastrous derailment. Later and more powerful locomotives had eight driving axles, assembled in two identical trucks, each main truck being prolonged and supported at its outer end on a pivoted motor guiding truck. This type of wheel-base may be defined as Bo.Bo+Bo,Bo Auxiliary control of the angular deviations of the guiding trucks was necessitated in order to suppress hunting motion at high speed.
The importance of metallurgy to the engineer. 767-72.
Very general paper which advocated a greater understanding by engineers of iron, steel and other metals as materials. "The principles underlying the heat-treatment of steel are not really difficult to understand, and a knowledge of this subject is essential to-day... Engineers are generally mystified by the phenomenon known as fatigue. There has recently been a revival in the use of wrought iron in places where it had been replaced by steel. It is said to be less subject to fatigue, to resist shock better, and to corrode less rapidly than steel. If these claims are true, its use may well be justified in spite of the fact that its tensile strength is less. Steel castings are widely used, and when properly made they are very reliable... Engineers are meeting great difficulty from the phenomenon known as creep". Ends with corrosion and pitting.
Volume 124 (1933)
The compression-ignition engine and its applicability to British railway traction. 3-33. Disc.: 34-61.
Advantages of the oil-electric system
Fuel cost approximately halved.
In most cases one engineman only required
no standby losses.
Fuel transportation charges greatly reduced.
large saving of water is effected.
Man-hours are saved in the running shed by the elimination of fire lighting, boiler washing, and locomotive requirements (i.e. fire cleaning, turning, and taking water).
Continuous 24-hour day service can be obtained when necessary, and the engine is at all times available for immediate use. Refuelling points can be placed as conveniently as are water cranes.
Smoke and waste steam are eliminated, together with their deteriorating effects on buildings, rolling stock and passengers clothing. Dead fires, smokebox ash and boiler scale in shed pits and on the rail side are absent, thus saving labour in their removal.
General cleanliness of the railway is improved.
The production of a vacuum in an air tank by means of a steam jet. 231-65. Disc: 266-300.
Academic research perfgormed at Bristol University. Author mentions vacuum ejectors for railways, but neither representatives from the railways nor from euquipment suppliers appear to have attended the meeting. The main results of these experiments given with reference to continuous air flow conditions through the ejector were:
(1) Over-expansion of the steam in the nozzle took place during all the tests described, as this gave satisfactory results over a wide pressure range, but a high vacuum could also be produced by an under-expanded jet.
(2) The series of stationary waves in the steam jet, upon which the successful action of the ejector appeared very Iargely to depend, extended for a certain length outwards from the nozzle.
(3) With a steady admission steam pressure and over-expansion in the nozzle the photographs showed that the stationary waves varied thus : (a) wavelengths increased (and therefore the overall length of wave series) with increased vacuum; (b) waves swelled transversely with increased vacuum, and vice versa in both cases. These results were deduced from separate experiments using an air Pump.
(4) A direct deduction from (3) above was that the wave series was more " tapered " in form when discharging against a gradually rising pressure along its length (working conditions in air ejector) than when the jet discharged into a region of nearly uniform pressure (air pump conditions).
(5) When a sliding diffuser was moved inwards over the jet the vacuum increased and a position was reached when the core of the jet, with its layer of entrained air, probably just filled the throat entrance. A sudden rise of about 5 inches to the higher range of vacua then took place, and the globular part of a wave was always observed to be inside the throat after this sudden rise. If the movement of the diffuser was continued, and if the diffuser had a long parallel throat, another smaller rise would take place at the next wave.
(6) It is evident from (5) that the correct setting of the throat entrance relative to the nozzle outlet is a very important length, and its determination is entirely omitted in the theory of the ejector. The maximum value of this length was found to increase with increased steam pressure, and it was evidently some function of the wavelength in the jet outside the nozzle. At a steam pressure of 140 psi. by gauge for the particular nozzle used, the maximum value of this distance was practically two wavelengths.
(7) In a diffuser with a long parallel throat (a length equal to two diameters was used) at the higher vacua, vigorous waves extended right through the throat into the entrance of the tail piece. This type of diffuser admitted a longer and more powerful jet than the one with a very short throat, and it gave a higher and more nearly constant vacuum over a wider range of diffuser setting.
(8) Of the two forms of diffuser entrance used, namely (a) short rounded and (b) tapered, the latter gave, on the whole, better results than the former.
(9) The performance of a steam-operated air ejector should be based on the calculated nozzle discharge and not on the condensed steam collected. The percentage of the true steam weight carried off by the entrained air leaving the condenser varied very considerably on different days, but values as high as 25%t were obtained.
(10) Low steam pressures were found to be unsuitable. The lower limit in these experiments to give a high vacuum with a fairly good steam-air ratio was about 120 psi by gauge. At this steam pressure the vacuum produced was nearly 25 inches and the steam-air ratio was 10.4, the steam quantity used being the calculated nozzle discharge when the initial superheat was 10°F.
The investigation of the mechanical breakdown of prime movers and boiler plant. 337-479.
Volume 125 (July to December 1933)
Factors affecting the grip in force, shrink, and expansion fits. 493-535.
Diesel traction. 537-613. Bibliography (95 citations). 36 diagrs.
Read before the North Western branch in Manchester on 5 October 1933, and before the North Eastern branch in Newcastle upon Tyne on 28 March 1934. Intriguingly this Russian-authored paper began with a brief historical sketch of locomotive development in England. .
Locomotives with a reciprocating non-condensing steam engine have three serious disadvantages:
The presence of harmful horizontal and vertical forces which produce recoiling and hammer blow. In the latter respect a considerable inclination of the cylinders is especially harmful.
Excessive fuel consumption. The overall efficiency of the Planet was less than 2%, and for the very latest steam locomotives of the reciprocating type did not exceed 11%. On the other hand, even a second-rate motor car has an efficiency of more than 20%. The two-stroke double-acting diesel engines of the German battleship Deutschland showed an efficiency of about 40%
On suburban lines electric traction has had a more definite success, nevertheless only 1.6 per cent of the worlds railway system has so far been electrified. The reasons being:
Losses between power plants and trains are very considerable. Electric locomotives do not consume more than 14% of the energy in the fuel burnt at the central power plants. On the other hand, the efficiency of the engines in omnibuses and lorries is over 20%.
Electrification approximately trebles the capital irretrievably sunk in a given transport scheme. According to the most recent data the cost of electric locomotives is only 18% of the total cost of electrification, the cost of the wiring and substations being 40%, and that of central power plants 42%
No possibility of moving electric power stations in accordance with fluctuation of traffic. Self-propelling locomotives are, however, transportable. Therefore, when there is a sudden and temporary increase in the traffic of any given district, supplementary motive power can be quickly sent to that district, and equally quickly removed again when it is no longer required.
Fuel:.Precise experiments made in Germany, Italy, and the Soviet Union,
both on "testing blocks" (test rigs) and on the track, have established that
the average efficiency of diesel locomotives is over three times as high
as that of the best reciprocating steam locomotives. On the other hand, the
same experiments show that the efficiency of any diesel locomotive depends
not only on that of the Diesel engine itself, but also on the transmission
and method of control.
In the U.S.A., 600 h.p. Diesel-electric shunting locomotives showed over a period of two years a maintenance cost of £93 per thousand hours, whereas this cost for corresponding steam locomotives 22 was £556. The former figure is, however, doubtful because for certain 300 h.p. Diesel locomotives the cost of maintenance 22 reaches £194.
Volume 126 (1934)
The mechanics of a locomotive on curved track. 457-61.
LMS Research Department.
Outlined some methods of calculating the flange forces acting at the wheels of a locomotive or of any other rail vehicle running on curved track. For this purpose, a locomotive is considered as an assemblage of trucks variously linked together, a truck being defined as "any number of wheel pairs held parallel to each other in a frame". Thus a 2-6-4 tank engine consists of three trucks, the leading pony truck constituting the first, the coupled wheelbase the second, and the trailing bogie the third. When a truck runs on curved track, continuous slight slipping takes place at some or all of the wheels, whether the latter are coupled together or not. It is possible, however, to imagine a point, within or adjacent to the truck wheelbase, such that if a wheel were placed there, of the same diameter and coupled to the other wheels of the truck, it would undergo pure rolling without slip, either longitudinally or laterally. This point is termed the centre of friction of the truck. Cited Uebelacker..
Concluded with three actual examples:
0-6-0 engine, weight 51 tons, passing slowly round a 40-chain curve without superelevation ; flange force, 7.1 tons at leading coupled wheel.
2-6-4 tank engine, weight 86½ tons, travelling at 60 mile/h round a 40-chain curve superelevated 3 inches ; flange forces, 1.0 ton at pony truck wheel, 4.3 tons at leading coupled wheel, and 4.6 tons at leading bogie wheel.
4-6-0 express engine, weight 85 tons, travelling at 70 mile/h round a 308-chain curve superelevated 31/8 inches; flange forces, 4.6 tons at leading bogie wheel, and 13.2 tons at leading coupled wheel. The latter figure is sufficient to cause derailment, and in fact the conditions corresponded with a recent accident (Weaver Junction, London Midland and Scottish Railway, 1930), where the leading coupled wheels of an express locomotive became derailed on a curve at high spced.
Volume 127 (1934)
Coker, E.G. and Levi, R.
Force fits and shrinkage fits in crank webs and locomotive driving wheels. 249-275
This experimental investigation relates to a general method of measuring stress distribution when force fits and shrinkage fits of the plane stress type are employed in engineering practice. Important cases occur in the webs of built-up crankshafts for locomotives and diesel engines. When the latter are of high power and short stroke, so that crankshaft and crankpins are large and relatively close together, the initial constructional stresses are shown to attain high values.
More complicated cases, from an experimental point o! view, occur in the driving wheels of locomotives with a tyre shrunk over a wheel centre having a crank and balance weight integral therewith, while the main axle and crankpin are forced or shrunk in. Such a case is examined with reference to a driving wheel of the London Midland and Scottish Railway locomotive Royal Scot, and the stress distributions measured in various parts of a model of it are described in detail.
Volume 129 (1935)
Relation between theory, experiment, and practice in journal bearing design. 435-75
Volume 130 (April to October 1935)
Recent developments in hydraulic couplings. 75-157. Disc.: 158-90.
The first hydraulic coupling to be applied to a diesel locomotive was on a 300 h.p. locomotive, (illustrated Fig 39) constructed by Hudswell Clarke and Company, Ltd., early in 1930 for the Junin Railway in Chile. Discussion: T. Horbuckle (LMS, 166-7); J.F. Alcock (Hunslet, 167-9) spoke about the locomotives supplied to the LMS;
Haworth, H.F. and A. Lysholm
Progress in design and application of the Lysholm-Smith torque converter, with special reference to the development in England. 193-230. 9 illus., 26 diagrs.
Voith turbo transmission. 231-47. Discussion (with two above Papers): 248-70.
T. Hornbuckle (261-2) noted the co-operation with Haworth in the design of railcars for the LMS.
Volume 131 (1935)
Coker, E.G. and Salvadori, M.
Stress waves in the tyres of locomotives. 493-512.
When a locomotive wheel rolls on the track, the tyre is squeezed between the wheel centre and the rail. The former acts as a roller of variable springiness at each point of its periphery owing to its necessarily intricate shape, while the rail also offers a springy resistance which changes at every point between a pair of chairs. The result of the mutual pressures exerted by the wheel centre above and the rail below is to produce a stress wave of variable intensity in the tyre as it advances along the rail, with a peak value immediately over the contact area when no tractive effort is being exerted. A photo-elastic investigation of one case of a stress wave travelling in a tyre is described in the paper as an illustration of a number of others of practical interest.
Volume 133 (1936)
[Presidential address]. 251-65. 3 tables.
An account of the development of the A4, plus a testing plant appeal.
Investigations in film lubrication. 413-72.
...fluid friction conditions. The second short section deals with experiments on a Deeley friction machine and shows the effect on the boundary friction of the...
Volume 134 (1936)
The air resistance of passenger trains. 91-160. Disc.: 160-208.
Engineering Research Officer, London, Midland and Scottish Railway, Derby.
Study of air resistance, including the effects of oblique winds, performed in a wind tunnel on reduced-scale models of LMS and LNER passenger rolling stock. The main investigation related to trains comprising a locomotive and six coaches, in which the aerodynamic forces on each vehicle were separately measured ; the effect of train length on the resistance of the last coach was determined ; and hence the resistances of trains up to twelve coaches in length have been estimated. The forces on the bodies and chassis of certain coaches were also separately measured.
O.V.S. Bulleid (172) "was quite unable to understand how a theory as to what would happen with a full-size train under working conditions could be built up from results from small models, obtained under such different conditions. He thought Commander Cave- Browne-Caves suggestion, that a relationship should be established between the results for models and for actual trains, was an essential requirement. There was a tendency to encourage engineers to think that streamlining would effect savings in train working which, in practical experience, would not appear possible. He felt, moreover, in view of the London Midland and Scottish Railway Companys magnificent run from Euston to Glasgow in 6 hours with an ordinary train worked by a Pacific engine not streamlined, that the air resistances could not be anything like as high as the figures suggested in the paper. The subject of streamlining was, he thought, still very much in the initial stages and required considerably more investigation."
Some factors affecting the design of heat transfer apparatus. 363-411. Disc.: 411-35.
Lawford H. Fry (414-15) regretted that though the paper gave evidence of a great deal of work and collected a large amount of information useful in connexion with heat transfer, the information was presented in such an unsystematic fashion that it was very difficult to disentangle the thread of the argument and to apply the formulae to specific cases other than those dealt with by the author. He had spent several hours trying to apply the processes described in the paper to the problem of computing the heat transfer in the flue of a locomotive boiler. The results obtained were not consistent with observed values, and he was not sure whether this was due to difficulty in understanding and applying the methods recommended or whether the methods could not be extended to cover the case of the flue. From an analysis of locomotive boiler tests it was found that the following figures were typical. A flue of 2 inches inside and 2¼ inches outside diameter, 250 inches long, surrounded by water at 388° F., carried 288 lb. of gases of combustion per hour. The gases entered at 2,080°F, containing 549 B.Th.U. per lb. and came out at 614°F., containing 149 B.Th.U. per Ib. The heat given up by the gas was 400 B.Th.U. per Ib., representing a total of 115,200 B.Th.U. per hour for the flue. As the flue had 10.9 sq. ft. of inside hcating surface the rate of heat transfer was 10,580 B.Th.U. per sq. ft. of surface per hour.
Volume 135 (January to May 1937)
Kitson Clark, E.
Engineering through the nations. 533-7 + 4 plates. 8 illus.
Volume 136 (1937)
Proceedings, General Discussion on Lubrication and Lubricants, 13th-15th
October. 119 et seq
Other reports covered intrnal combustion engines by Ricardo, turbines (Auld and Evans) and properties and testing (Gough).
General discussion on lubrication. Group II. Engine lubrication (reciprocating steam engines). 139-43.
French and German State Railways consider that various grades of superheater cylinder oil are desirable according to the degree of superheat obtaining in the cylinder, whereas the Canadian National and English railways employed only one grade. Of the opinions expressed about superheater cylinder oils, the majority favoured compounded oils, since it was considered that at the temperature of superheated steam the oil becomes much less viscous and the fatty oil is partly decomposed, the decomposition products helping in the formation of stable and resistant boundary films. Of special interest was the use of emulsified oil, prepared by the German State Railways from superheated steam cylinder oil and lime water, for use in locomotives working under medium loads.
German State Railways used winter and summer grades oils for journals, motion, etc, as did some English railways, whilst Canadian National and many English railways prefered the same grade throughout the year; one English railways considered that the inconvenience of changing the grade of oil twice a year outweighed any possible advantage and in its experience no advantage was obtained when the thicker summer oil was used. It was the practice of the English railways to use a mineral oil containing a percentage of refined raw rape oil, the percentage depending on the different classes of work and the experience of the companies concerned, whereas the German State and Canadian National Railways used mineral oil only. German State Railways used a higher viscosity oil for lubricating the journals and gear of streamline locomotives, this also being the practice of some English railways.
German State Railways used wick trimmings to supply oil to the valve gear, and to connecting and coupling rod bushes: English railways used worsted trimmings for the valve gear and either worsted trimmings, needle trimmings, or felt pads for the rods.
The application of the locomotive to traffic working. 333-52. 8 diagrs.
Methods for analysing of steam locomotive power during traffic working on railways lacking special testing facilities. The determination of cylinder and boiler output, the treatment of locomotive and train resistances, and the application of these factors to train loading, speed, and running time. The calculation of fuel and water consumptions on a horse-power-hour basis is given, also the method of application to train working. Then describes the procedure for the practical application of locomotive power to trafiic working, and the measurement of train capacity in terms of ton-kilometres per train hour. The engine evaluated was one of a batch of 2-8-0 goods engines on the Central Uruguay Railway.
Short biography of George Stephenson. 373-91.
Selected for publication in connexion with the centenary in 1938 of Holy Trinity Church, Chesterfield, in which George Stephenson is buried, and the proposed building of a George Stephenson Chancel in the church. Pp. 386-91 are extracted from the J. Scott Russell presentation made in 1848. Records the meeting of Stephenson with the great American writer, Emerson, in Chesterfield early in 1848 at Whittington House, the home of Frederick Swanwick. Emerson remarked later that it was worth while crossing the Atlantic were it only to have seen Stephenson-he had such force of character and vigour of intellect. He seems to have the life of many men in him. But he was a stricken man and the end came only a few months later. Includes photographs of Stephenson's tomb and memorial tablet, his birthplace and a portrait of him.
Volume 137 (1937)
Diesel traction on railways. 135-43. Disc.: 143-64. 6 diagrams
An analysis of various locomotive operating costs and the degree to which each is influenced by the type of tractive unit selected, namely, steam or diesel. The effect of possible higher availability or serviceability factors with diesel locomotives was not likely to be as high as may be supposed. Specification and design details of the various components of a diesel tractive unit are discussed and in the particular case of a locomotive designed to haul a load of 600 trailing tons at a maximum speed of 60 mile/h., the main design data and performance curves are worked out with and without supercharging. The general conclusion was that diesel operating costs compared with steam became increasingly favourable as the power output required from the tractive unit decreases, when the advantage of a self-propelled vehicle, such as three unit railcar, over a train hauled by a locomotive became more pronounced.
The adoption of large diesel locomotives was likely to be restricted to fast heavy goods traffic, and long-distance through passenger services. In India opportunities for their application would be particularly limited. The climatic and operating conditions will tend to accentuate the disadvantage of great weight and high first cost, and the reduction in fuel and lubricating oil expenditure as compared with steam traction is not likely to be such as to compensate for this fully, at the then prices of coal and fuel oil.
Locomotive operating expenses comprise mainly : (a) capital charges, i.e. interest on capital and amortization ; (b) fuel ; (c) repairs and aintenance ; (d) crews wages ; (e) lubrication ; (fi)water, and (g) auxiliary services, namely, engine shed, watering and coaling faciiities, turntables, etc. The economic application of Diesel traction will depend on the extent to which its characteristics can be utilized, under the particular operating conditions obtaining, to reduce the various items of locomotive expense.
Discussion: Oliver Field Allen (ALCO 144-5) wrote to state that the capital cost in the USA for diesel traction had fallen to less than twice that for steam. L.F.R. Fell (151-4) cited his own paper presented in 1933 noting that as indicated by the author's general conclusion, the operating costs of Diesel locomotives, as compared with steam, became favourable only when the weight of the unit to be propelled was comparatively low. G.V. Lomonossoff (156-9) claimed that in the USSR steam locomotive mileages had reached 9000 miles per month and that this had increased the competition against employing diesel traction.
British engineering societies and their aims. 333-44.
The activities and objects of the Institution of Civil Engineers and the Institution of Mechanical Engineers are described, with notes on other national and local associations in Great Britain. Forms an excellent survey of the general history and state of British institutions and learned societies in the late 1930s. Paper presented at the Semicentennial Meeting of the Engineering Institute of Canada, in Montreal, June 1937 ; reprinted by arrangement with the Institute.
de Soyres, Bernard . The birth and growth of engineering in the West
Includes Richard Trevithick and engines and pumps built in Cornwall by Fox, Williams and Company, of Perran Foundry, and by Harvey and Company, of Hayle Foundry. Brunel is mentioned, but mainly for his marine activities.
Volume 142 (July-December 1939)
Lightweight passenger rolling stock. 13-32 + 16 plates.
This paper makes no attempt to compare British and American practice because of the wide difference in operating conditions prevailing in the two countries. Developments which have taken place in the last seven years on the LMS are described, showing the improvements in the conventional British passenger coach. This originally consisted of a separate riveted steel underframe and timber-framed body, but to reduce weight without sacrifice of strength, welding and high-tensile steel have been employed and timber gradually eliminated. This has resulted in an increasing identification of the underframe and body which has produced an all-steel coach giving a weight of about 500 lb. per passenger seat. Means adopted include the body side and underframe combined into the form of a Vierendeel truss, the design of which is briefly described, together with the method of calculating the stresses in the different members. On the constructional side, the layout of the shops and the special presses and tools are dealt with. A method of unit assembly has been adopted and both spot and arc welding are largely used. Details are given of the erection into a complete coach, and of the overload tests made on the finished structure. Particulars are given of the savings in weight attained, and the paper concludes with suggestions as to the direction in which further progress may be sought in the future.
Introduction. In this paper no attempt is made to compare British with American practice. The requirements are so different. Variations in climatic conditions alone necessitate an entirely different practice and the restrictions imposed by the smaller loading gauge in Great Britain call for an entirely different treatment.
In Great Britain, largely owing to high platforms at the stations, the maximum width over the cylinders of a locomotive is 9 feet and the maximum height 13 ft. 6 in., but generally only 13 ft. 1 in. The maximum weight on an axle is 22 tons 10 cwt. (50,000 lb.), and this limits the tractive effort of a six-coupled engine to about 40,000 lb. The maximum weight of a train is therefore not more than 600 tons,-/- so that to enable a reasonable number of people to be carried with the comfort necessary for comparatively short runs, it has been the practice to build coaches 60 feet in length and weighing 30 tons.
In the past this was achieved by having a steel underframe and a body frame of wood with wooden panelling and roof, but for many years now the general practice has been to have a heavy steel underframe on which is mounted a wooden-frame coach body sheathed in steel and with a steel roof. An attempt will be made to show the trend of British design and the various stages through which it has passed in the effort still to build 60-foot coaches not heavier than 30 tons each.
High-speed lightweight trains. 97-111.
Author was Chairman ASME Railroad Division. The purpose of this paper is to outline the changes which have occurred during the last five years in high-speed passenger train cars and in motive power for hauling them and the economic factors which have brought about these changes. The new designs for passenger cars and the materials used in their construction are discussed. A detailed comparison of steam locomotive and Diesel-electric locomotive characteristics as they affect the operation of these new high-speed trains is presented, Test data are included to indicate the importance of comparative stress in track produced by the two types of power. Reference is made to the steady improvement which has been made in steam locomotive design, but it is shown that there is a need for some rather extensive experimentation to make this type of power more suitable for this particular class of service. In conclusion, the author presents his views on the general results which have been secured from the operation of these new trains and the probable trend in their future development.
An investigation into the occurrence and causes of locomotive tyre failures. 289-303 + 4 plates.
A detailed investigation was made by the LMS Research Department into the causes of locomotive tyre faihres from two standpoints: first to determine the cause of any particular failure, and second to find general relationships between effect and cause in the matter of tyre defects. Examples are given of the examination of individual failures, and of experimental work directed to the improvement of wheel and tyre. In a statistical review, it is shown that fatigue is the major cause of tyre failure, and many of the factors which might influence the development of fatigue failure have been critically examined and their responsibility assessed. In conclusion it is noted how, by a change in tyre boring methods to increase the effective fatigue strength of the tyre, and by modifications in design to ensure more uniform stress distribution in the tyre, the occurrence of fatigue failures has steadily declined.