Journal of the Institution of Locomotive
Volume 33 (1943)
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Journal No. 171
Sillcox, L.K. read by Julian S Tritton (Paper No.
Power to pull: a comparison of the operating charcteristics exhibited by steam and diesel-electric locomotives. 4-30. Disc.: 30-76.
Fourth Ordinary General Meeting of the Session held at the Institution of Mechanical Engineers, Westminster, on Wednesday, 29 July 1942, at 6 p.m., the President, Mr. O.V.S. Bulleid, occupying the chair
This was an American paper and was intended to show the advantages of diesel traction.
The author's comclusion is "Viewed in its entirety, one can but conclude that the Dieselelectric is making steady progress but a definite prediction as to the extent which it will replace the steam locomotive could not be supported by sound reasoning and would, therefore, be unwarranted. The Diesel displays unquestionable advantages for yard assignments, is peculiarIy adapted to certain high-speed passenger operations, and is being installed in freight service to a limited extent. The controversy will be decided finally on strict economic principles and the ultimate selection depends, to a large extent, upon the ability of the Diesel-electric manufacturers to offer their product at a price comparable with that of the steam locomotive. Should this be accomplished, the position of steam as the motive medium would be precarious. Steam locomotive designers are energetically attacking the problem of dynamic augment due to overbalance because of its serious limitations to high speed but the elimination of the problem The substitution of Diesel power would enable the elimination of costly boiler water preparation facilities, water service towers or track pans, and of unsightly coaling plants. It would remove the necessity for roundhouse properties as we know them which could be replaced with modern attractive maintenance plants. The entire tempo of the railway would be changed. Diesels would operate to reduce the number of terminals required and to this extent would largely affect an overall improvement in railway operating practice, both with respect to the economy of movement and to the dispatch with which tonnage is handled. Perhaps this is the important aspect of the entire problem of railway modernization made possible through the use of the Diesel; the aspect that should be emphasised more than all others, thus eliminating excuses to stop trains in transit unnecessarily. Further,. if the practice of handling traffic in train load lots is forced upon the railways by competitive rate situations effected through other forms of transport attempting to obtain the traffic, it merely signifies that railway traffic will represent unit movements covering great distances between originating and final terminals with no intermediate attention affecting train consist required. Railways have put one future ; namely, to handle traffic at wholesale rates and to discontinue conditioning rates upon a retail basis".
Possibly because there was a reduction in the number of papers presented during WW2 it produced a considerable response. E.C. Poultney (30-2); J.S. Clayton (32); E.S. Cox (32-4) who commented strongly on the hammer blow associated with two-cylinder locomotives; John Alcock (35); O.S.M. Raw (35-7); E. Graham (37);
Major O.S.M. Raw, R.A.O.C. (35), reierring to the rise in cost of steam locomotives since 1937 mentioned in the paper, pointed out that in 1937 the steam locomotive industry was very depressed, and willing to build at uneconomic prices, so that prices were bound to go up in the following years. Certain savings resulting from fhe use of Diesel locomotives were, he said, mentioned in the paper, but the chief saving in all the calculations which he had seen so far had been due to the elimination of the fireman, and whether one was allowed to do away with the fireman depended principally on what the trade unions had to say on the subject. The paper also maintained that the Diesel locomotive saved the time required for boiler washout, which was a very decided saving ; but, having been responsible for some Diesel locomotives in Ceylon and India he knew that it was necessary to offset against that the time spent on cylinder overhauls, which was considerable ; and in Ceylon at least two hours had to elapse after an engine came in from the line before the engine room was cool enough to send a fitter in. He would be interested to know more about the type of motors fitted in the Diesel-electric locomotives which were referred to as running at 100 m.p.h. He understood that axle-hung motors were normally used, and that axle-hung motors were normally limited to about 75 m.p.h. Surely the use of axle-hung motors at high speed accounted for the abnormally rapid track wear. The Author stated that Diesel locomotives could stay out in the yard for six days, which was an undoubted fact; indeed, he believed that the L.M.S. shunters carried fuel on them for six days. On the other hand, in the Calcutta docks and on the South African Railways the steam locomotives stayed out of the shed for six days also, with merely a cleaning of the fire-bars when the crews were changed over, so that there was not such a great saving there as seemed apparent. The elimination of water costs was put down in the Paper as a big saving, and undoubtedly it was; but when Diesel locomotives were used it was necessary to put in very special plant to service them. It was not possible to deal with Diesel locomotives in an ordinary shed ; it was necessary to have it dust-proof. He thought there was a great future for the Diesel locomotive for shunting, for rail motors, and for high-speed trains, but they would have to go a long way yet before they were used as main line heavy locomotives, because they involved having such a box of tricks all bottled up together, requiring a B.Sc. as driver. There is one further point, that is the employment of travelling maintenance staff. The Author suggests that on easy sections a portion of the power plant, the locomotive being built up from a number of individual units in multiple control, being shut down and serviced en route. As stated, my experience in India and Ceylon is that on a high-powered unit some considerable time must elapse from the time of shutting down the power unit until the engine room is cool enough. to work in. Surely it would be better to cut off the redundant power unit over the easy section and have it overhauled in a shed under better working conditions. The unit under power would also be saved the effort of hauling the unit under overhaul. The Paper presupposes that there is ample power for all purposes in the modern Diesel-electric locomotives in use in America, but I recollect having read that on Rocky Mountain sections a steam pilot locomotive is used with all forms d Diesel powered trains.
Mr. E. Graham (Member) expressed some doubt as to whether the labour costs given in the Paper were complete. The Author did not clearly state, he pointed out, what staff was employed. Leaving out of the question entirely the yard shunting locomotive, where the case for the Diesel was, in his view, undoubtedly established, and considering only the big Diesel-electric locomotives, he wondered what staff travelled with them on long runs. They were very complicated, with a great deal of auxiliary machinery, and a previous speaker had referred to them as a box of tricks. It was a little difficult to imagine the ordinary steam locomotive driver and fireman taking care of such machines on, say, a 2,000 mile run. There is a hint in the Paper that additional staff were carried, because it is mentioned that there is the great advantage of b&ng able to couple up two, three or four machines and use them as required, and to the possibility if some part of the equipment of one unit failed of putting that unit out of action and repairing it while the train continued on its journey. That pre-supposed that shop staff was carried on the train. His own impression was that mechanics were cafried on each of the very big units on long runs. He doubted whether account was taken of that in the figures relating to running costs, but it might be that the cost was covered in the all-in- repair cost. On that he would like further information, if it was available.
D.R. Carling (37-40) on smoke abatement and comment on the steam locomotive failures cited in the paper on the Norfolk & Western Railroad; Mr. D. R. Carling (Associate Member) said he wished to make some remarks in support of what Mr. Cox and Major Raw had said. Mr. Cox made some remarks on Figs. I and 6 which were very much to the point, but in addition there was undoubtedly a discrepancy of some kind in Fig. 6, because the tractive effort curves over a considerable length lay almost together, and yet there was a steady difference all the way along in the horse-power curves. There was something wrong there, which might explain Mr. Coxs difficulty. Which curves were correct he would not like to say, because he had not had the time to make any calculations. The question of smoke was referred to several times in the Paper. A great deal in the way of smoke abatement had been done on the railways in America, but the locomotives still gave out much more smoke than was the case in this country. It was worse in! America than in this country because the American locomotive did not have a closed ashpan, and therefore unless working at a fairly high output and being fired steadily, if there was any unburned coaI on the grate the locomotive gave out clouds of filthy black smoke, and that had led to the by-laws in many American cities prohibiting the use of steam locomotives. It had already been mentioned that the price at which steam locomotives were sold a few years ago was not economic, it being a question of the state of the market and of competition. Something of the same sort applied to the Diesel locomotive. Competition had been increasing. A few years ago there were fewer firms producing Diesel-electric locomotives, especially high-speed types, than the;e were now, and it might be partly competition which was reducing the price. At the same time, the increasing market for steam locomotives was permitting an increase in price, because the builders were no longer at their wits' end where to sell anything at all. Another point which should be mentioned was that the maintenance cost of steam locomotives was known to rise rapidly with age for a given mileage per year. The cost per year would rise very considerably as the age of the locomotive increased, particularly under United States conditions of really heavy working ; and that made it essential, in all such comparisons as those made in the paper, to know the average age of the motive power. Taking as an example the figures given for freight locomotives on pages 27 and 28 of the Paper, the steam locomotive was built in 1938 and the Diesel in 1941 ; in other words, the Diesel was in its first year of life. If the steam locomotive had been in its first year of life, he believed that the repairs would have been so much cheaper as to reverse the saving of 34d. shown. In a few years' time the steam locomotive would cost more, and what the Diesel locomotive would cost was not yet known, or at least if any figures were available he did not think that they had been published yet. The trend of repair costs for Diesel locomotives with increasing age would be very interesting, when figures became available. Only time could shew what it would be
O.V.S. Bulleid (42-4) was highly critical of the US steam locomotice costs quoted in the paper;
C.E. Fairburn (written communication 44-7 quoted in full) wrote that Dr. Sillcox, in his most interesting paper, defined the position of Diesel-electric traction as an effective compromise between steam and electric motive power, which presumably implied that it might be used to replace either, but so far as this country, and indeed most parts of, the world, were concerned, asked if it should not be regarded as complementary to these syslems? There were, said, undoubtedly many applications for Diesel units on both steam and electric lines but, except perhaps in some rather special cases, it was doubtful if it could be justified as the sole motive power. He maintained that on lines with heavy traffic the fundamental advantages of electric traction must rule out the Diesel. One of those which was often overlooked was. in the provision of prime movers as distinct from the transmission equipment, viz., the total horse-power rating of the Diesel engines needed for any service, was the sum of the rating of all the individual locomotives required, whereas on an electrified line provision had to be made only for the maximum power demanded at any one time. The rating of the power station plant needed for that was very considerably lower than that of the Diesel engines which would be needed if that form of traction were adopted ; in addition, the supply was usually taken from a system feeding an industrial load as well and the diversity between the two loads gave a substantial reduction in the proportion of the capital expenditure on generating plant which could be charged against the traction load.
At the meeting, which, unfortunately, he was unable to attend, one speaker suggested that performance as such was the deciding factor in choosing a traction system and that, if improvement in cleanliness were needed on steam operated lines, that should be obtained by air conditioning but the criterion was surely performance in relation to total cost and if the fitting of air conditioning equipment to all passenger coaches on a railway were taken as the alternative to Diesel or electric traction, it would certainly be more costly, and did not affect the cleaning and maintaining of stations, buildings, and the outside of the stock on steam lines. The Paper compared steam and Diesel locomotives on the basis of horse-power but, by itself that meant very little. A statement of horse-power must be associated with a duration before it could be used as a rating to compare different units. Thus Dr. Sillcox gave the indicated horse-power of certain steam locomotives he mentioned, but were the figures the maxima which the locomotites could maintain continuously or were they for some shorter period, such as one hour or even five minutes? The rating of an electric locomotive was normally given as the sum of the ratings of its motors, usually on a one-hour basis and other figures on a continuous and a momentary basis were generally stated also. However, that method could not be applied to a Diesel-electric locomotive as the output was always limited by that available from the engine ; in practice, owing to the variable voltage and current conditions to be met, the total rating of: the motors on a normal traction basis was usually considerably greater than that. The rating of a Diesel locomotive could, therefore, only be based on the power available from the engine and the time for which it could be maintained and also whether it was measured at the engine coupling or at the wheel tread must be stated. As the transmission efficiency varies with operating conditions, the relationship between figures measured at those two points was complex; quite apart from any power taken from the engine for auxiliary purposes.
If fuller information on those lines could be given for the locomotives dealt with in the Paper, the data already included might be of considerable value ; at present it could not be properly assessed. Apart from a comparison on a horse-power basis, the relative weights of the steam and Diesel locomotives were important provided that the class of work was the same in each case. In British practice that applied specially to shunting units where all the ,weight was adhesive and so determined the maximum tractive effort which could be expected. It was, however, necessary to make some correction for the even torque of the Diesel in comparison with the steam unit. This was illustrated in the table on page 22, where the Diesel locomotive was shown to have an adhesive factor of 33 per cent. compared with the steam figure of 22 per cent. only. To sum up, what was wanted was a basis of comparison which accurately reflected the traffic capabilities of the different locomotives; ability to perform a given service was what really mattered.
He said the figures for the annual mileage of both Diesel and steam locomotives given in the paper were surprisingly large, and wished to know in what degree they were representative of general practice in the U.S.A.? It seemed that they must be based on a few services where conditions favour large mileages, and it would be interesting to learn to what extent traffic in the U.S.A. could be arranged to give such figures generally, provided, of course, that the types of locomotives employed were suitable. In this country, the limit here was set much more by traffic conditions than by the capabilities of the locomotives.
Regarding the characteristics curves given in Fig. 6, there appeared to have been some slip, e.g. if the tractive effort characteristics of the steam and Diesel locomotives cross at 60 m.p.h. the driver horse-power characteristics also should cross on the same ordinate. In Fig. 1 the drawbar horse-power was given instead of the driver horse-power and that was perhaps better, as it compen46 sated in some degree for any differences in weights of the two types of locomotive which were not given. In Fig. 7 the steam locomotive characteristics were clearly only approximate, as they should have a horizontal portion at low speeds. That was the most important part of the curve for shunting locomotives and as drawn, the curves did not show very clearly the rather important differences between the two types. It would be an advantage also if they showed the limits set by adhesion since, as already mentioned, the even torque of the Diesel-electric locomotive gave it a distinct advantage in this respect.
The life of the Diesel was estimated at 15 years. In the present state of development some units may be obsolete in a shorter time than this, but there was no obvious reason why, when design had had time to become more stabilised, the life should not be comparable with that o the steam locomotive as all wearing parts could be replaced in the ordinary course of maintenance. It would be interesting to have Dr. Sillcox's views on the use of nose-suspended motors on high-speed Diesel locomotives. Those motors were generally recognised as being satisfactory in regard to track stresses up to moderate speeds, but in electric locomotive design some form of flexible drive was almost universally used for high speed units. It appeared that certain forms of such drives which occupied relatively little space might be adopted with advantage on *high-speed Diesel units. Could any of the effects ascribed in the Paper to the low centre of gravity of the Diesel locomotive be due in some measure to the nose-suspended motors ?
The L.M.S. 250 h.p. Diesel shunting locomotives at present required refuelling at 12-21 day intervals, depending on the yard where they were working, and in new designs somewhat greater tank capacity would probably be provided to enable a long uninterrupted period to be operated in all yards. It was also expected that a general overhaul would be necessary only ever! three years. On that basis the theoretical technical availability would be at least 95 per cent., including time spent in shed maintenance. It was difficult to comment on the operating costs given in the paper owing to the different conditions, different relative costs of fuels and smaller units used in this country. A 0-6-0 tank shunting locomotive of some 45 tons weight costs not much more than half as much for fuel as the shunting locomotives quoted at the top of page 26, and the cost of fuel oil for a 350 h.p. Diesel was about two-thirds of that for the 600 h.p. American unit. The saving on fuel was, therefore, relatively lower, in addition the other costs for the steam locomotive, particularly repairs and water costs appeared to be very high. Nevertheless the L.M.S. had been able to establish the Diesel-electric shunter at least in its more intensively worked yards. Perhaps Dr. Sillcox in his reply could cover interest and depreciation charges in those comparisons more fully ; interest appears to be excluded and the life on which depreciation was based was not given.
The first cost of steam and Diesel locomotives given also differed considerably from those obtaining here. Recently the ratio Could it be taken as 15 years in all cases? of the cost of Diesel to the cost of steam units had been rising and what might be described as the price spiral which had always handicapped the Diesel showed no sign of breaking. In order to be really useful to a railway, Diesel units had to be employed in reasonably large numbers, otherwise the maintenance and other standby costs become too great a burden for the Diesels to carry. Also the total market open to a manufacturer had a large influence on first cost. But the manufacturer was unwilling to risk quoting prices on the basis of a reasonably large sale to a wider market, and the railway companies in turn would not risk ordering large numbers of locomotives of a type which for most applications was still unproved in this country. Action had to lie with the manufacturers as they had a potential world market, while each railway was limited to itself. That must now, of course, await the end of the war, but the outbreak of war could not be regarded as the reason for the very slow progress made here up to the present as there were few signs of rapid development before, and in fact the manufacturers were more conservative than the railways. As already mentioned the railways were able to establish the shunting unit at least for some duties, but the manufacturers seemed unable to follow that up and produce a locomotive on an economical basis for large scale use on other services.
H.H. Andrews (59-50) was critical of the dismissal of electric motive power in the USA;
T. Henry Turner (53-4) A good case had been made out for the use of Diesel-electric shunting vehicles at marshalling yards, but he thought the Author did not make any reference to tunnels. It seemed to him that Diesel-electric vehicles would be preferable to steam vehicles on, for example, the Metropolitan line passing through Baker Street, where the sulphurous fumes were at times most objectionable to the crowds of passengers. The same could probably be said for the rather special Kings Cross Hotel tunnel on the L.N.E.R., and possibly some others, such as the Severn tunnel, might also be operated by Diesel-electric vehicles.
He realised that many of the tunnels in this country were on main lines and therefore had to be passed by steam locomotives for many years to come, but wherever it were possible to substitute Diesel-electric, the amount of corrosion of the rails and other fittings in the tunnels would be much reduced and the maintenance simplified. He had not mentioned Woodhead, as the electrification which was started on the lines, including that tunnel, was already well in hand. In his work he had constant reminders of the abnormal corrosion in tunnels and therefore thought the Author might be interested in that point. The substitution of Diesel-electric for steam locomotives in suburban services would seem to be justifiable in view of the acceleration characteristics, but whether that be so or not, it would result in an appreciable reduction in the smoke nuisance.
Clarke, C.W. (Paper No. 440)
Service tests to establish locomotive efficiency. 77-90.
On the GIPR in India
Journal No. 172
Vittoné, Jose (Paper No. 441)
Notes and observations on diesel electric railcars on the Buenos Aires Provincial Railway. 94-156. illus., 9 diagrs.
Please note the Peper number is duplicvated. Second Quarterly Meeting of the South American Centre Session, 1941, was held at La Plata, at the Workshops of the Buenos Ayres Provincial Railway on Monday, 1 September 1941, at 9.30 a.m. Translated from Spanish.
four Diesel-electric railcars of the Buenos Aires Provincial Government Railway were acquired in the year 1935 and up to the 31 December, 1940, they had been in service practically five years, and the present time is considered opportune to give an account of certain details and technical results of their working in the hope that same will be useful in the study of, and solution to, some of the problems which arise in connection with this modern branch of railway transport.Abstract in Locomotive Mag., 1943, 49, 183.
Journal No. 173
Robson, T. (Paper No. 441).
The counter pressure method of testing locomotives. 171-98. Discussion:198-217+ folding plate. 5 illustrations., 12 diagrams. (including 2 side elevations.)
Please note the Peper number is duplicated. Presented on 24 March 1943 in London, but a precis with some diagrams appeared in Locomotive Mag., 1939, 45, 78-80..
In order to save expense the Author attempted to use one locomotive only, although it was appreciated that the extra power absorbed per cylinder might cause difficulties. An old 4-6-0 locomotive with outside cylinders and piston valves, built in 1906, was put at his disposal and the necessary alterations made, the French practice being followed. When about 600 horse-power mas being absorbed, the metallic packing was melted out of the piston and tail rod glands, so the water injection was led to the centres of the cylinders instead of into the steam chests, the supply was much increased and the glands were lubricated mechanically. These alterations were an improvement, but when attempting to absorb 900 horse-power, the driving axleboxes heated badly. These were steel with an inserted bronze bearing in the crown, and the side faces were too small to withstand the heavy side thrusts. Solid bronze axleboxes, without any white metal, were fitted to the driving axle having large bearing surfaces on the inside of the wheel boss, and three oil feeds were supplied to each box, one syphon feed to the wheel boss and one syphon and one mechanical feed at the rear
Includes details of the tests performed on the B17 class locomotive No. 2811 Raynham Hall. Whilst the data are presented in graphic form, the precise location and dates are not given
The Author wishes to thank Dr. F. Aughtie and Mr. F. M. Colebrook , of the National Physical Laboratory, for helpful criticisms during the design of the circuits used, and Mr. C. Jarvis, Mr. P. Dobson and Mr. D. Carling, members of his staff now engaged on more important work, for the help received in the development of the apparatus mentioned, and also Mr. E. Thompson, the Chief Mechanical Engineer of the London and North Eastern Railway, for permission to publish the results given in this Paper.
Pp. 206-7 : Comment on the Vitry tests with P2 class 2001 Cock o' the North, Contributors to the discussion included E.S. Cox, O.V.S. Bulleid, H. Holcroft and E.C Poultney..
E. C. Poultney (198-9) , who opened the discussion, prefaced his remarks by thanking the author for contributing such a very interesting and valuable Paper to the proceedings. He hardly knew which part of the Paper to admire morethe graphic description of the testing or the very pointed remarks on locomotive design, and particularly with regard to valves. He felt that he could not usefully make any observations on the question of testing, except that probably the method which had been outlined, while very ingenious, must require an enormous amount of rehearsal before the results desired could be obtained. Inasmuch as each point plotted on the diagrams represented a separate test, the results were obviously extremely good; the points were very close together, and there was not much discrepancy between one test and another when the same specific object had been in view.
So far as the results obtained at various cut-offs were concerned, he could not but think that the Author had perhaps been a little unfortunate, because while personally he would be the last to criticize the performance of the locomotives of the London and North Eastern Railway, in view of the excellent work that they had done and were doing, he thought that on the whole the valves employed on them were very much too small for the cylinders, judged by modern standards. On the other hand, the cylinder design adopted for the B.17 type locomotive used in the tests did not lend itself very well to the adoption of what might be called a full-sized valve. The arrangement was, he thought, well-known, and was shown in the accompanying sketch. The three valves were all in line, and the position of the frames prevented the fitting of a valve of proper size for the centre cylinder. When the Gresley Pacifies were first built they had cylinders of 20-in. bore, and an 8-in. valve, while modern practice would be to employ an 11-in , or 12-in. valve with a 20-in. cylinder. That made an enormous difference to the power which could be obtained at an earlv cut-off.
It was of interest, in that connection, to study a diagram, Fig. 17, published in The Engineer, 23 May, 1906, which showed the performance of a Great Western Railway locomotive with 18-in. by 30-in cylinders with l0-in. valves. At 18 per cent. cut-off and 63 m.p.h., the drawbar horse-power was 800; at 20 per cent. cut-off and 58 m.p.h. it was 900; and at 23 per cent. cut-off and 60 m.p.h., 1,100 drawbar horse-power was shown by the dynamometer. Those figures were far in advance of those obtained with the B.17 type engine dealt with in the Paper, and he thought that that was clue entirely to the fact that the valves were large in proportion to the cylinders. The figures he had given, moreover, were obtained with a saturated steam locomotive. If he were a chief mechanical engineer, he would have that chart exhibited in his drawing office; it was a wonderful example of what could be done with large-size ports and valves to get the steam into the cylinders and out again.
He thoroughly agreed with the author's remarks with regard to the design of cylinders; he was sure that there was a great deal of room for improvement. He knew that there were strong objections to the use of very large and heavy valves, which threw enormous stress on the valve motion. There were also strong objections to the use of small valves, because it was difficult to get the power reguired. There was probably very good reason, therefore, to do away with them altogether and use poppet valves.
E. S. Cox (199-) said that great credit was due to the author and his colleagues for having done so much useful work and for obtaining so much valuable information by what were relatively simple and inexpensive means. The London and North Eastern Railway, however, enjoyed certain advantages, the absence of which might preclude other railways from following quite so simple a method, the principal one being a stretch of line 44 miles in length of almost unvarying gradient, for the most part dead level. Similar tests made abroad had also been carried out on long lengths of level track, or at any rate track with only a gentle and continuous gradient.
Some reference was made in the Paper to the fact that the L.M.S. Railway, which had been considering the use of the type of testing in question before the war, were proposing to develop it by the use of electrically braked vehicles. That was done not from any desire to make the tests more complicated or more expensive, but because on that railway there was not a sufficient length of level track, comparable with that to be found on the L.N.E.R., and also because it was desired in the L.M.S. tests to bring in the question of coal consumption, for which purpose it was felt that at least an hour's run would be necessary, in order to stabilise conditions in the fire. An hour's test at 70 to 80 m.p.h. meant a continuous run of more than that distance, and on the L.M.S. there was no level or even continuous up-grade track of that length; the best piece of track which could be found would include both up and down gradients, and in those circumstances the problem of the regulation of speed was likely to be very much more difficult than on the L.N.E.R. or in the case of the tests carried out abroad. For that reason the electrical method was decided upon, simply because it gave the assurance of very accurate control under widely differing conditions of running resistance, He regretted that it was not possible to give any comparable results of tests on the L.M.S" for the units had only just been completed when the war broke out, and no data were vet available,
The author had referred to Figs. 5 and 6 of the Paper as containing the most important of the deductions made from the tests, and they did in fact confirm in a nutshell the result of all the investigations made by M. Chapelon, underlining the importance of freedom through steam ports and passages. It would be interesting to hear from the author what practical steps were taken, in view of the information so disclosed, in order to obviate on actual engines the difficulties disclosed by the diagrams. In that respect the omissions from the Paper were rather tantalising, because it was well known that the L.N.E.R. had a number of locomotives with poppet valves, and it: would be very interesting to hear whether those valves, with their separation of inlet and exhaust events, and the possibility of better valve opening at early cut-offs, had shown any signs of bringing- about the improvements which were so much to be desired.
He was sorry also that the author did not show in the Paper what an actual indicator diagram looked like when taken by the cathode-ray and photographic method referred to in the Paper. It would be of particular interest to know whether that method gave a diagram which corresponded exactly in its area and characteristics with a diagram taken by an ordinary Crosby indicator on the same engine under conditions where it was known that it could be fairly accurate, as for example at slow speeds. If that could be shown it would be a step forward, because he felt that while it was necessary to develop and utilise the cathode-ray indicator to a much greater extent in future, some form of comparison with the older type of diagram was desirable in order to give confidence in its use for measuring power output.
A.F. Webber, (201) speaking as one who himself had been engaged for some years on engineering research in industry, remarked that his experience during those years entitled him to say that the work disclosed in the Paper was engineering research work of the highest order. Every credit was due to the author and his colleagues for the work which they had done and for the successful conclusion to which they had brought it.
Turning to some points of detail in the Paper, he did not think that the author had fully explained the effect of the port opening. In the first diagiam showing the drawbar pull against speed for different cut-offs (Fig. 4) there was a certain trend going on up to and including the 35 per cent. cut-off, in that the slope of the line was steadily steepening; but at 45 per cent. cut-off there was a reversal of that trend. He understood that that was due to the increasing port opening, but, if that was so, he would have expected that it would become apparent gradually. Instead of that, up to and including 35 per cent. cut-off the port opening did not seem to influence the position, the drawbar pull falling off with increasing steepness, while at q j per cent. cut-off there was a sudden reversal of that trend. Fig. 5, which was used to show the marked increase in drawbar horse-power when the cut-off was increased from 15 per cent. to 25 per cent., was from one point of view a little unfortunate, because it should be noted that the zero was not shown on the diagram, the ordinates starting at zoo db.-1i.p. That had the effect of exaggerating to the eye the difference in drawbar horse-power between 15 per cent. and 25 per cent. cut-off.
On page 182 of the Paper there mas a remark which seemed to require some amplification. The author said: The pressure drop to the steam chest will be proportional to the amount of steam take:> by the cylinders. Strictly speaking, the word proportional, if it was not qualified, meant directly proportional, whereas, in fact, the pressure drop would be proportional to the square of the steam flow. He thought that a correction should be made there, as otherwise readers might be led astray. Further, one should be very careful about taking a system resistance as equivalent to an orifice. The pressure drop across an orifice arose primarily from the convI:rsion of a certain amount of pressure energy to kinetic energy. The pressure drop across such a system as the regulator, superheater elements and steam pipes was chiefly due to frictional resistance, and the characteristics were not identical with those for the pressure-velocity conversion.
With regard to smokebox temperatures, although the point was, perhaps, not strictly relevant to the main thesis of the Paper it would be interesting to know whether any steps were taken to make traverses with a thermocouple to ensure that the point finally selected for the test was an average temperature in the smokebox, and also whether any tests had been made with a high-velocity suction thermocouple to ascertain the effect on the ordinary sheathed couple which he assumed, in the absence of any statement to the contrary, was used; because such a couple, if of fairly large dimensions (5/8in. or ¾-in. in diameter), would be very seriously affected, so far as the temperature which it attained was concerned, by its surroundings, by which he meant the front tube-plate of the boiler, which was approximately at boiler-water temperature, and the rest of the smokebox shell, which was at some temperature intermediate between the gas temperature inside it and the air temperature outside. He had had some experience of that problem of gas temperature measurement, and he thought that it was not an over-estimate to say that in conditions which were roughly similar to those at present in question the thermocouple reading might be 50°F. to 100°F. lower than the true gas temperature.
A point which occurred to him as being of great importance if successful steps were to be taken to overcome the difficulty at the inlet ports at early cut-offs was the following. If the drawbar horse-power at 15 per cent. cut-off was increased sufficiently to maintain constant drawbar pull, it would, of course, mean a very great increase in the steam demand on the boiler. As the cut-off would remain at 15 per cent., the exhaust pressure would presumably remain more or less constant, and he would suggest that the repercussion on boiler design would be very serious, because the boiler would have to produce this increased quantity of steam without any help from increased blast-pipe pressure.
A final comment, though a minor one and one even further removed from the main thesis of the Paper, was that according to ordinary financial reasoning a company was not, as the author seemed to suggest, insolvent if it could not pay dividends to its shareholders, but only if it could not pay its debts.
D.R. Carling ((202-) (the only member of the author's dynamometer car staff who was able to be present) said that to the main description of the tests already given he could add very little, except to say that the tests occupied about a fortnight on the line, and, due to the traffic-passing on the line in question, it was usually possible to make only one run in each direction daily. That was often a severe handicap. When Professor Lomonossoff initiated constant speed testing in Russia in 1908, his test trains were g iven equal priority with the Tsar's train, and all ordinary traffic had to give way to them. It was improbable that such a position would ever exist in this country, but possibly a little more help in that direction might be received from the Traffic Department in future. The Paper necessarily condensed into a small volume a large amount of work done in the tests, and when one little point was shown on a graph with a small figure against it, it meant that a great deal of work had gone into establishing that figure from genuine data. Unfortunately they were not able to complete their work on the indicators. They had just reached the tantalising stage when they intended to photograph the screen and obtain some final results when Hitler threw his spanner into the works, and any further work had to be postponed. The same thing applied, of course, to any altera- tions in design which might have been based on the results of the tests carried out. There was no doubt that the slide shown by Mr. Poultney did indicate how far in advance of all others the G.W.R. were at the date in question, and the effect on design on the L.N.E.R. of the locomotive exchange between the two railways was too well known to need detailed description. It was quite true that it was extremely difficult to get larger valves of the ordinary type into the space available in the British loading-gauge with three cylinders, especially with the conventional British plate frame, and probably it would become necessary to use entirely independent inlet and exhaust valves at each end of the cylinder-either poppet valves, as Mr. Poultney suggested, or independent piston valves , as used by M. Cossart on the former Northern Railway of France.
. A point of considerable difficulty in dealing with the test equipment was that the locomotive under test was housed in the ordinary engine sheds, and all the apparatus hac! to be designed with that fact in mind, because one never knew when one's carefully made indicator was going to receive a clout from the shovel of ~ passing fireman, or when some similar mishap would occur to other apparatus. All delicate equipment had to be dismantled every night. When he had the honour of accompanying the author to France they had been greatly impressed by the fact that for certain tests which were being done there a large electric express locomotive was placed permanently at the service of the experimental section, which was provided with adequate accommodation for it, and only at times of great traffic activity was it returned to the Traffic Department, as a favour. There could no doubt that an improvement in the conditions under which tests were carried out would greatly simplify the apparatus used, and probably the value of the results obtained would far outweigh the cost of providing the equipment.
As a result of tests on a single locomotive class in Russia before the last war, Professor Lornonossoff succeeded in saving annually about ten times the total cost of his experimental depart- ment.
The difficulties in developing the new indicators had often been very discouraging and it was due to Mr. Robsons persistence that so large a measure of success had been attained. H. Holcroft (203-)said the author had done the Institution a great service by describing the latest form of locomotive testing, which is comparatively new to this country, although it has been used on the Continent for some time past. It would be of interest if the Author would give some indicator diagrams showing the action taking place in the cylinders of the counter-pressure engine. If information of that kind was available, it would be a valuable addition to the Paper.
While it simplifies the procedure and facilitated research by enabling constant conditions to be maintained and unwanted variables eliminated the system described in the Paper should not be regarded as seperseding all other tests. there being at least five methods of testing locomotives. There was first of all direct observation from the footplate in actual service, with or without a measured coal and water over-all lest. That method was of value in assessing the fitness of the design to carry out the intended duties, and it was purely an operational test. Then there was testing by means of the dynamometer car with a train attached, which recorded the actual work done: by the engine over a particular route with a given load and speed. It was very difficult to evaluate the dynamometer record accurately in this case because the inertia effects of the locomotive on the -drawbar with varying speed added plus and minus quantities to it which had to be allowed for, and it was not at all easy to assess the correct amount of acceleration or deceleration taking place at any moment. Then there were indicator trials, and these were run, with or without coal consumption tests, when no dynamometer car was available. The author had described the latest form of testing with the dynamometer car and a braked load, and the advantage of that method, of course, was that it was possible to get steady conditions of speed and so plot the results more accurately and thereby determine what the engine would do under any given circumstances. Finally, there was testing with stationary plant; and that had some advantages where development was concerned, and some disadvantages. For instance, the drawbar pull recorded was not the true reading which would be obtained on the line, because the atmospheric and track resistance were not present, and only the machine resistance was deducted from the indicated horse-power, and, of course, there was the absence of the cooling effect due to the passage of air over the hot surfaces of the engine. All five methods have their particular merit in one direction or another, and they should be regarded as being complementary rather than competitive.
He was very interested in what was said in the Paper with regard to the low efficiency at 15 per cent. port opening, and would like to suggest to the author the use of a piston valve of half the normal diameter and twice the travel, which he thought should gi"l."e greater port efficiency. The greater inertia forces set up by the acceleration of the valve would be largely balanced by the lighter weight of the valve, so that the valve gear itself would not be subjected to any more loading.
It had to be remembered that the 15 per cent. cut-off was only a nominal figure, and the clearance volume in the cylinder modified its value very considerably; ordinarily, IS per cent. nominal cut-off represented an expansion rate of about 20 per cent. ; but here again at fast engine speed the diminishing aperture in the closing phase of the valve while the piston was moving at high velocity resulted in very little steam getting through approaching cut-off point, and, as speed increased, this amount decreased, the cut-off really becom- ing limited by the time factor rather than by the precise action of the valve, so that a 15 per cent. cut-off became virtually 12 per cent. or less with increasing speed.
The author also suggested the lengthening of the cut-off to 85 per cent. to give greater starting effort, but' the difference in mean effective pressure between 75 per cent. and 85 per cent. was scarcely appreciable, and one would be using 10 per cent. more steam to little purpose. On the other hand, an improved starting effort, i.e. the avoidance of dead centres, would be the chief advantage; but, while that might be desirable in the U.S.A., where there were long close-coupled trains with automatic couplers, and setting-back at starting was to be avoided, it was scarcely needed in this country, where there was usually sufficient elasticity in the drawgear for the engine with a 75 per cent. maximum cut-off to be able to make enough angular movement to open the second cylinder to steam. The longer travel required for an 85 per cent. maximum cut-off adversely affected the valve gear design and was at the expense of the short cut-offs. The author suggested a reversion to the two-cylinder engine and the lightening of the reciprocating parts; but two-cylinder engines must have at least 40 per cent. to So per cent. reciprocating balance if they are to run satisfactorily at speed, whereas the latest multi- cylinder engines were without any reciprocating balance" and there- fore with these engines the bridge stress diagrams recorded were smooth parabolas as compared with the jagged saw-tooth diagrams obtained with two-cylinder engines, and, because the bridge stresses were so much lower, three or four-cylinder engines were allowed a higher static loading on the wheels, and therefore had more adhesion than could be obtained with a two-cylinder engine. The lightening of the reciprocating parts involved the use of alloy steel, and that again raised difficulties, because the liability to hair-cracks and so to fatigue-fractures was much greater, and also the parts could not be handled by the shed staffs in the way that plain carbon steel parts could be. If parts had to be sent to the works for attention engines were held out of traffic so much longer.
Still on the question of reciprocating parts, he would like to suggest that mass was actually beneficial in the short cut-oft's at high speed. With a IS per cent. cut-off there was a large steam load at the beginning of the stroke tailing off to very little at the end, whereas the reciprocating parts by their inertia absorbed some of the steam pressure at the beginning of the stroke and gave it out towards the end, with the result that there was a very much more even turning moment at the crank shaft. It had been proved by test on more than one occasion that the least internal resistance of an engine coincided with evenness in the 'turning moment, and a point which might very well be investigated by the new method of testing described in the Paper was how to get the most beneficial weight of the reciprocating parts in relation to the variation of pressure and cylinder diameter. Owing to less internal friction with even turning moment, it did .not necessarily follow that the maximum indicated horse-power or most economical point of cut-off necessarilv coincided with maximum drawbar horse-power or most economical production of power at the drawbar; it might be, for instance, that lengthening the cut-off and easing the regulator would result in a more even turning moment, and therefore an actual increase in drawbar horse-power or decrease in steam consumption per drawbar horse-power hour.
In conclusion, he would like to support the views held by the author in regard to the limited opportunity for engineers in executive positions to enter into technical investigation under present circum- stances. With regard to the remarks of Mr. Poultney on the Great \Vestern Railwav dvnarnorneter record illustrated bv him, it should be pointed out that 'that exceptional result was obtained with a well- designed Stephenson valve gear, and in his (the speaker's) experi- ence the Stephenson valve gear could give much better results than the \\' alschaerts , although the mechanical arrangement of the latter made it preferable in modern locomotive design.
The President (O.V.S. Bulleid 206-), in closing the discussion, said he had known the author for many years, and did not think there was a better experimental engineer in the country. Another of the author's great merits was that he had no hesitation in saying exactly what he thought.
Personally, the Paper had made him think a great deal, because he did not like to have it said that locomotive engineers did not know so much about the steam engine as they ought to know, and particularly that they could not get steam into their cylinders. On thinking it over, however, he came to the conclusion that there must be a mistake there, because locomotives had been and were being built which ran very fast and pulled very hard; and so he came to the conclusion that the author had forgotten two things: time, and the inertia effects of'steam. The author did not pay enough regard to the weight of the steam, but almost contemptuously disregarded the necessity for large steam pipes and, above all, for large steam chest volumes immediately adjacent to the valve opening, while concentrating on the peripheral measurements of ports, based on extremely badly-designed ports with unnecessary bridges, so getting a false picture. The author might also be wrong in not taking into account the volume behind the piston and the rate at which that volume was increasing; had he asked himself whether the steam would have anywhere to go if he had a bigger port opening? M. Chapelon had stated definitely that there was a good deal of illusion about the poppet valve with its separated phases, and that what was of prime importance was the location of the piston at any given moment; it was no use having big port openings to feed a volume which did not require feeding, Personally, therefore, he thought that the reason for the failure of the B.17 locomotive to develop higher horse-power at 70 rn.p.h. should be looked for in other directions than a port opening of the order of that in question. In his own practice, and with the dimensions employed, he found that the steam had more time to fill the volume available at 15 per cent. cut-off than at 25 per cent. cut-off. The point, therefore, seemed to need considerably more explanation than it had so far had.
On the general question of testing locomotives, he had always been entertained by the fact that in France there were two completely hostile schools. There were the engineers in charge at Vitry, who were convinced that Vitry provided the only way in which to carry out tests, and there was M. Chapelon, who was quite certain that the results with the Vitry plant were most misleading and deceptive. When, therefore, the testing plant at Rugby was finished, the best thing would be to have Rugby plus the counter-pressure, and, probably better still, the electric braking agent, complementary one to the other.
The author trod on very delicate ground in his reference to multi- cylinder engines. The" Channel Packet" Pacifies, owing to weight restrictions, could not have been built as two-cylinder engines. The benefit of the absence of reciprocating balance was clearly shown on bridge tests, and he, was sure that no two-cylinder engine had ever been designed which could give such a smooth bridge deflexion curve. Another problem involved was that of the piston load; there, would have to be a load on the piston of 45 tons, or something of that order, and that would present a problem not easy of solution. The author's indicator was extremely interesting, and it was a pity that the war put a stop to the work, becauseit was not possible to be happy about indicator diagrams at present, and if the author could produce a real indicator diagram which would, at long last, show where the true point of cut-off was, locomotive engineers would be extremely indebted to him.
Written contribution from Dr. G. V. Lomonossoff.
All methods of testing locomotives can be divided into two basic groups:- ( 1) Under service conditions, and,
(2) Under constant conditions;
and the latter into three sub-groups:
(2a) On the test plant.
(2b) On the track with an auxiliary locomotive
(or· the counter-pressure method), and -
(2c) With trains on very long grades.
Generally speaking tests (2) under constant conditions are much more costly than those under service conditions (I). Consequently tests (2) can be justified only in cases where the relation looked for cannot be established under service conditions. But all relations presented by the author in his interesting Paper can be and were established under service conditions by many experimenters. As a matter of fact the measurements of speed, drawbar pull, temperatures, vacuum and taking indicator diagrams require only a few
Journal No. 174
Parker, C.R. (Paper No. 442)
Some notes on experience with railcar oil engines in the Argentine (with particular reference to repairs). 241-302; Journal No. 175: Disc.: 314-362.
First Ordinary General Meeting of the 1942/43 Session was held jointly with the Diesel Engine Users Association in the hall of the Institution of Mechanical Engineers, Storeys Gate, S.W.1, on Thursday, 5 November 1942, at 2.30 pm., Mr. O.V.S., Bulleid, President, occupying the chair and supported by Mr. G. E. Windeler, President of the Diesel Engine Users Association.
An extended abstract appeared in Loco Rly Carr. Wagon Rev., 1942, 48, 201 under the heading: Diesel Vehicle Repairs A consideration af the maintenance and repair methods of diesel locomotives and railcars compared with those of steam locomotives indicates that the life of either type of unit may be virtually unlimited. It has not been uncommon practice to. glorify the performance of steam locomotives 30, 40 and 50 years old, regardless of the fact that at such an age there is little of the original locomotive left except the spaces between the wheels. Similar methods may be applied to. the engines and mechanical portions of diesel locomotives and railcars by routine renewals, and by building-up through welding and by metal deposition.
This passible similarity of the methods applied to. steam and diesel power an railways was not featured in the remarkably comprehensive paper an the repair of railway oil engines on the Central Argentine Railway presented recently by Mr. C. A. Parker, of that line, to the Diesel Engine Users' Association, and read in London, on November 5, before a joint meeting of that Association and the Institution of Locomotive Engineers. But that paper did result. in an appreciation of the way and degree in which the proportions of a maintenance-and-repair programme may vary. For example, with. the Chicago-California and other long-distance diesel-powered trains in the United States the travelling-fitter system and the work done during a few hours of lie-over time at each end of the run, mean that say, 75 or 80 per cent. of all maintenance and repair work comes under the heading of maintenance, and that repair work "within the meaning of the Act" is undertaken only at infrequent intervals. On the other hand, the method practised on the Central Argentine Railway for the power plants of the 12 twin-car 640 b.h.p. Ganz diesel sets incorporates the mmimum of shed work, and the running department has teen relieved of the responsibility for engine maintenance except for odd details, practically all of the necessary work being carried out in the course of visits to the central repair shops. The claim is made that this Central Argentme Railway practice in no way invalidates "preventive" maintenance and repair, which is probably the key to the successful running af motive pawer of all types. On the Central Argentine system the power plants are taken to. the repair establishment for a light overhaul every 43,000 miles, and for heavy repairs every 125,000/140,000 miles, and It is judged that these mileages enable attention to be given to all the major and minor constituents before they begin to give trouble either through excessive wear, fatigue, or deterioration. Nevertheless, the extent to which the Central Argentine Railway has relieved the running department of much minor work and tuning-up the engines is greater than found on the majority of railways owning diesel stock, and possibly the success with which this has been done may be traced in a large measure to. the fact that these twin-car trains are concentrated in one area and work an certain definite services without variation. For mare widely-scattered vehicles it would seem that the shed staffs would still have to. be entrusted with a greater proportion of the total maintenance-and- repair work. These remarks, of course, apply to. medium and large-sized railways, for an the smaller lines maintenance and repair are usually undertaken in the same shed by the same men just as they happen to be needed.
Although a certain amount of trouble has been experienced with the main constituents of these oil engines an the Central Argentine Railwaythe shopping periods, for instance, seem to be governed by the mileage which can be expected before trouble is g;iven by the inverted main bearings bolted to the light-alloy crankcaseMr. Parker's paper emphasised the feature which has been found in practically all diesel railcars designed and built from about 1937 onwards, and that is the great majority of failures booked against the vehicles are not due to the engines or to the gearboxes themselves, but to. the auxiliaries associated with those two main constituents, Many of these troubles are trifling, and may result in the lass of only a few minutes on schedule, or a day laid off. On the other hand, the consequential damage resulting from the failure of a relatively unimportant part may be great, and that is one of the principal reasons for the necessity of an immediate advance in the standard of design and construction of all ancillary equipment. Far too often the standards have been almost nonsensical, and if found in conjunction with a conscientious running department officer who. books every defect, however small, may give a totally incorrect impression as to what modern diesel locomotives and railcars can do in the way of performance.
Journal No. 176
Shields, T.H. ( Paper No. 443)
The evolution of locomotive valve gears. 368-448. Disc.: 448-60. 1944, 34, 260. 2 illus., 100 diagrs., 2 tables. Bibliog.
The list of valve gears covered in this historical survey is very extensive, but is not completely comprehensive. It includes several which may not have been fitted to locomotives. Some gears for stationary engines may have doubtful authenticity, such as the involvement of Humphrey Potter (see Dendy Marshall in the discussion). The gears covered included those by James Watt who had learnt German to be able to understand Leupold's Theatrum Machinarum, William Murdock, William Symington, Richard Trevithick and his locomotive. Before the application of engines to locomotives and ships there had been little need to reverse. Engine, Cam and Frame Gear, Stop Valve Gear, Narrow Cam and Ring, Cam and Box Gear, Loose Eccentric, Carmichael's Gear, Bury's Gear, Gurney's Expansion Gear, Melling's Gear, Bourne's Link Motion, Hawthorn's Gear, Gray's Expansion Gear, Drop Hook Motion, Bury's Double Eccentric Gab Motion, Stephenson's Double Eccentric Gear, Pauwel's Gab Motion, Stephenson's Gab Motion, Rodger's Link, U.S.A. Gab Motion, Dodd's Wedge Motion, Dodd's Spiral Sleeve Gear, L. & S.W. Rly. Gab Motion; Fenton's Sliding Eccentric Gear; Crampton's Valve Motion; Eastwick's Sliding Block; Johnston's Reversing Valve; Hawthorn's Expansion Gear; Gozenbach Expansion Gear; Meyer Expansion Gear; Routledge Expansion Gear; Polonceau Expansion Gear, Guinotte Expansion Gear; Carbey Expansion Gear; Longridge Expansion Gear; Nasmyth Expansion Gear; Forrester's Gear; William's Link Motion; Howe's Link Motion; Howe-Stephenson Link ,Motion; Solid Bar Link Motion; Link Motion, Dub's and Co; Link Motion, G.I.P. Rly; Link Motion, L.M.S. Rly; Crampton's Locomotive Kinnaird.; intermediate driving shaft loco.; Gooch Stationary Link Motion; Angele's Link Motion; Walschaerts' Valve Motion; Heusinger Valve Motion; Walschaerts' Valve Motion (GSWR version), LMS version, William Mason modification for application in USA in 1875; Allan Straight Link as employed by Beyer-Peacock and on LSWR; Stewart's Link Motion; Cam and Link Motion (U.S.A.); Taylor's Shifting Eccentric; Von Landsee Link Motion; Hackworth's Radial Gear; F.C. Marshall's Radial Gear; Bremme's Radial Gear; Brown's Valve Gear; Kitson's Valve Gear; Morton's Valve Gear; Strong's Valve Gear; Joy's Valve Gear and as used on LYR and by Andrew Barclay and Sons; Ouest Valve Gear; Southern Valve Gear; J.T. Marshall's Gear; Bryce Douglas Valve Gear; Deeley's Cross Drive Gear; Churchward's Cross Drive Gear; Young's Cross Drive Gear (U.S.A.); Beames Walschaerts' Valve Gear; Stephenson-Molyneux System; Berthe Valve Gear; Baker Valve Gear; Valve Gear developed by Andrew Barclay and Sons; Webb's Loose Eccentric; Conjugated Valve Gear by Gresley and by Caledonian Railway; Poppet Valve Gears: Durant-Lencauchez; Caprotti; and R.C. Type (A.L.E., Ltd.); Fluid Pressure Gear-Meier-Mattern System; and Bulleid Radial Valve Gear.
It will be generally accepted that for the period 1843-1910 the Howe-Stephenson link motion was the most popular form of valve gear, although the' Gooch, Allan and Joy gears were, each in their turn, keen rivals. From 1910 the Walschaerts gear gradually gained popularity. Perhaps in this country this was due to the slow but sure decline of the inside cylinder locomotive, in addition to larger types i-ntroduced. R.C. poppet valve gears may be the future means of steam distribution in locomotive cylinders. How- ever, from the maintenance aspect poppet valve gears will have difficulty in proving superior to the present narrow ring, long travel piston valve actuated by Walschaerts valve gear.
H. Holcroft (448) said that a feature of all radial valve gears, and also of valve gears with a fixed quadrant link, was that they gave constant lead; i.e. the amount of opening at the beginning of the stroke remained constant, but the angle at which the valve opened, of course, advanced with the notching up. In the case of a shifting link eccentric gear such as the Stephenson or Allan straight link motion, however, not only did the angle of advance increase with the notching up but so too did the amount by which the valve was opened, i.e. they gave variable lead. That was a most valuable asset of the Stephenson gear, in that the valve was well open for early cut-offs at the beginning of the stroke; and an engine with a Stephenson gear, if it was well designed, would give a larger mean effective pressure and horse-power for the same size of cylinder than other forms of gear operating reciprocating valves. By reduction of lead in full gear it gave greater accelerating power from rest.
All valve gears which derived their motion from cranks or eccentrics or from crossheads connected to .cranks produced an approximation to harmonic motion, but it differed from the simple harmonic m that there were some minor harmonics compounded with it.
A simple harmonic motion could only be produced from cranks by gears having infinitely long rods, and in practical application the restricted length of rods and their angularities gave rise to minor harmonics of which those of any consequence were small in amplitude but of double the frequency of the main harmonic and at a phase. of 90° to it, and these octaves had the effect of introducing variations in the movement of the valve which might be beneficial or otherwise. The length of connecting rod was another factor entering into the case. The merit of a gear of any type depended on its mechanical layout and proportions. There had always been a great deal of controversy about which gear was the best from all points of view, but apart from mechanical considerations there was little to choose between the numerous designs described by the Author, because they all generated more or less the same type of harmonic motion, notwithstanding wide differences in the mechanism employed.
It was largely a question of the-survival of the fittest from the mechanical aspect, simplicity, cheapness of construction, adaptability and freedom from undue wear deciding the issue.
E.W. Marten (449) described the Paper as a valuable record, in the form of a connected story, of the development of and research on valve gears over many years. He knew of no other publication, he said, in which so much information on the subject had been so well presented. The Paper indicated that a great deal of study had been given to the subject of steam distribution in the locomotive cylinder, but it was of interest to observe that the inherent disadvantage of the great majority of gears described was that they had fixed valve events, and it was not until towards the end of the Paper and therefore in comparatively recent years that one found efforts directed towards separating the events so as to make admission independent and unrelated to exhaust. No doubt the absence of competition from other forms of motive power partly relieved the drive towards improving cylinder efficiency, and. after all, the locomotive with a conventional type of valve gear did pull the train, and reasonably well at that; but what of the future?
It was in the future that he himself was chiefly interested and he would like .to ask whether the developme';t of the reciprocating steam locomotive was to be prosecuted as vigorously as had that of, fo; example, the Diesel engine, in which case the improvement of cylinder performance offered the greatest scope, being that part of the locomotive where there was the greatest thermal loss. "It was still a long way from the thermodynamic ideal obtainable of a maximum of some 20 per cent. With the probable further increase in steam pressures and superheat temperatures, if full advantage was to be taken of greater expansive workingor, in other words, if maximum use was to be made of the available heat drop in the steamit would seem that valve gears of conventional type must eventually be displaced, particularly for high-speed operation or where efficiency and economy in working were of importance.
As an example of the difficulties encountered with the higher superheats, he knew of one series of locomotives where it had been found that the temperature of the superheat was such that the piston valve liners were badly scored with the result that it had been necessary to blank off some of the superheater elements. On the other hand, with those locomotives of the same class equipped with poppet valves, the absence of this trouble made it possible to take full advantage of the superior steam efficiency of high superheat. In discussing the present Paper, he did not want to press too much the subject of the poppet valve; but he was dealing with the future, and it was in that direction that development would probably be found to lie.
There was a brief reference in the Paper to the Caprotti gear. It was certainly the case that that gear was introduced in Italy about 1920, but the present British-Caprotti gear was in many detail respects very different from the original, and much had been and was being done in developing it to suit modern conditions of working and to avoid difficulties of maintenance. He alluded to that because of the Author's conclusion but he felt that provided it was well designed and of simple construction, a poppet valve gear should stand up to its work just as well as a conventional gearin fact a cam-operated gear had much to its advantage on the score of maintenance because of its precision nature.
According to the Paper it took 35 years for the Walschaerts gear to be applied to a hundred or so locomotivesin other words, to become establishedso at that rate there appeared to be a reasonable prospect of the poppet valve gear becoming universal during the lifetime of many presentassuming that the steam locomotive itself survived, which he thought was questionable unless its efficiency was increased by more progressive adoption of modern improvements.
W. Cyril WilIiams (450) said the Paper was really an historical review and although of indisputable and lasting value to the Journal and must have entailed laborious research, no discussion was really invited. The Paper might have encouraged discussion if the Author had given his views on present or future valve gears. For instance, there was the Baker valve gear; about a week ago he had met an eminent American engineer who had since returned to the United States and asked him his opinion of this gear. His reply was: "You can cut it out; it is slowly disappearing." Is that so? If so, why?
Reference was made in the Paper to the maintenance aspect of the use of poppet valve gears, but the whole question of poppet valve gears would surely have to be very thoroughly studied as the speed of locomotives increased. In this connection he would like to mention that he had been most impressed, on a visit to Algiers just before war broke out, at the performance of the express Beyer-Garratt locomotives which were fitted with Cossart cam-operated vertical piston valves of the Nord type. They had been at work for several years, and ran with under 7 per cent. cut-off for more than one-third of the journey between Algiers and Oran, which is a distance of 262 miles. When one shut the regulator off one seemed to feel the whole engine leap forward, and high speeds were main- tained for several miles with a remarkably slow drop. The performance, whether at speed or on 1 in 40 grade was excellent and efficient. He would admit that it was a " bag of tricks," but the interesting fact was that at the time of the landing in North Africa 28 out of 30 engines of this class with that gear were found working, although no spares had been received for two years.
J.D. Rogers (451) said the Paper was an encyclopaedia on valve gears of the past, but personally, like Mr. Williams, he was more interested in the valve gears of the future. He had been surprised to .learn how many valve gears had been invented in America, but, strangely enough, the only two to " get anywhere" had been invented on this side of the Atlanticthe Stephenson and the Walschaerts. The Walschaerts gear was invented in 1844, it was introduced in America by the B. & O.R.R. in 1904, and applied to the first Mallet built there. In 1906, the railway on which he served his time bought experimentally two engines fitted with this "new" gear. They did not know a name for it, but called it the "monkey motion" because as the engine ran it had the appearance of climbing or jumping. The beauty of it to them was that it got away from the use of fixed eccentrics, and, in spite of the many virtues of the Stephenson gear, it is of no use in America to-day, because the speed of the very large eccentrics would be so great that it would be impossible to lubricate them. The Walschaerts gear therefore serves the purpose, and some of the largest and fastest engines in America to-day, hauling the crack trains, are fitted with well-designed Walschaerts gear and piston valves.
So far as his own recent investigations went, he did not find that with any of the high-speed engines doing the maximum of 70 to 80 m.p.h, there had been any great trouble with the lubrication of piston valves, and he was surprised to hear that there had been trouble on this side of the Atlantic. The valves used in America are sometimes 12 inches or 14 inches in diameter, of light design, but it took a good deal of power to drive them, steam pressures being 250-300 lbs. per sq. inch.
He had used the Baker gear, and many other types, including the Southern gear with the fixed horizontal link; but that was just one that passed as an experiment. In his time the principal objection to the Baker gear was the pin connections, with fixed beanngs. These collected lost motion quicker than Walschaerts gear, but now that it was on needle bearings it is doing a better job. Some of his friends told him that it was good only for freight and moderately fast passenger service, and that it did not give the distribution which was desired at high speed.
As far as poppet valves are concerned, there are only a few engines in America, built experimentally, which are using them. The Pennsylvania Railway has had several engines fitted, and some of the other railways. The most intriguing gear which had come under his observation is that fitted to the Merchant Navy class locomotives of the Southern Railway. When he first looked at the box and was told what was inside he was rather fearful that it might not do the job, but since he has travelled. on the engine and seen the gear in the shops, he has changed his mind. He wondered whether some gear of that type was not the answer to the problem of driving piston valvestransferring the motion from the axle to the three-throw crank, which was, he thought, novel in valve gear construction.
K. Cantlie (452) said there were only two points where he could add to the Paper in any way. One was that the ouestanding locomotives to be fitted with the Allan straight link motion were the L.N.W.R. Jumbos, which many people regarded as among the most astonishing locomotives for their size ever built. The other was with regard to the fitting of Dendy Marshall valves to the L.N.W.R. locomotive No. 1361 Prospero. The valves did not follow the fitting of the engine with four cylinders; the experiment was carried out to test Dendy Marshall valves.
He felt that in some ways it was a pity that the Author would not go one step further and indicate more fully than he had done why it was that the hundred and one gears descnbed in the Paper failed in their various ways, why they were not perpetuated. Some of them looked excelfent, but there must have been some fault or flaw in them. At the present date it was probably impossible to find out just what the trouble was, and in some cases, of course, the cause of the trouble was obvious; but in certain cases it might be of great interest if that information could be discovered. One curse of valve gears lay in the up-and-down motion of the driving axle in the horns, and that, if he might say so, had been found to be the trouble with the Southern gear. Perhaps Rogers would agree with that. That also affected the Joy gearnot seriously, perhaps, .but it could not have qeen a good effect .. A difficulty with a cross-connected gear such as the Deeley, which looked very fine on paper, was that it could not be worked on one. side, and if one side went the arrangement failed completely. That was a very important point which militated against cross-connected gears.
He thought it rather odd that the various types of flat valve, fitted with an expansion valve above or below them, were not perpetuated. The introduction of the link motion almost killed them, but before the link motion was introduced there was a very good reason for their use, ia- order to obtain expansive working of the steam. After the introduction of the Stephenson motion only a few efforts were made to continue their use. For working at very short cut-offs an expansion valve might have been worth the fitting, though history appeared to indicate that that was not the case. It might appear that the real reason was that the small steam pipes and small valve ports prevented working at very short cut-offs, but if that was not the reason then there should have been an advantage in putting in an expansion valve, because it would allow of freer exhaust, which was the point behind the use of poppet valves, etc. One had only to listen to locomotives passing to hear the very large proportion in which the beat was definitely out; and, when it was remembered that the beat had to be 10 per cent. out before one could hear it, it would be realised that there was room for improvement. With the Prince of Wales engines on the L.N.W.R., the driver used to be blamed for wire-drawing the steam and working at half regulator until the engines were indicated and it was found that with a boiler pressure of 175 lb. per sq. in. the pressure in the cylinders was 170 lb. and the back pressure 220 lb. That was one reason why the drivers did not like working with short cut-offs. The invention of valve gears appeared to be rather like the indicated horse-power of a locomotive; it rose very steeply when it started and gradually levelled off. After about 1860 it very much levelled off. That was an argument for the Stephenson and the Walschaerts being good enough, but, as had already been said, he did not think they would be good enough for the future.
F.L. Howard (453) said his shed experience on the Southern Railway was that there was not a large amount of trouble with valve gears. They had to deal with the Walschaerts gear in its normal form and in the modified form on the 3-cylinder engines, and with the Stephenson working with the straight shaft and also through the rocking shaft with piston valves on superheater engines, and they did not meet with much trouble; maintenance was yery light.
He did not think it could be said that the problem of lubrication had yet been solved. The old-fashioned slide valve had been a very wonderful fitting, and it gave good -perforrnance. They had a steam crane which had been in service for forty years, and it still had the original cast iron slide valves, and he did not think that they had worn 1/16th inch.
B.W. Anwell (454) said it seemed that a large number of people had worked in a large number of different ways to try to attain the same ends. It struck him that at the present time locomotive engineers were not being original enough, but were being content with small modifications of already well-established principles and not looking ahead as far as they should. The type of valve used on the internal combustion engine withstood terrific loads and temperatures continuously, and in view of that it seemed that for locomotive work the poppet valve principle had not been sufficiently developed. The poppet valve would appear to have a great future in front of it, and if it proved possible to devise some improved method of controlling the admission with the poppet valve they would be getting a little nearer to the results which they sought to obtain. good deal more could obviously be done on those lines with the development of alloy steels and other alloys which the war had produced, and once locomotive engineers were able .to make use of those materials they might be a little nearer the solution of their problems. Mennwhile, the old, radial types of gear did seem to be doing their job, and developments of them, and in particular the type used on the Merchant Navy class on the Southern Railway, with the oil bath, meant a definite step forward which would fill the gap until the poppet valve had been properly developed. He hoped that the reasons for the failure of earlier types of gear would be the subject of a Paper to the Institution in the future.
A.J.L. Winchester (454) said he had recently been reading a publication by C.G. Wolfe which came out in the early years of the present century and described the various forms of link motion. The three main forms were described in detail, and in the case of the Allan straight link motion it was stated that this gear, when properly designed, gave the best distribution of steam of any gear so far used; and that would include what was practically the modern form of the Walschaerts gear, but not the poppet gears. If the present Author could throw a little light on that statement, and explain just what was meant by " the best steam distribution," it would be of interest.
Bulleid (454-6) expressed his regret that it had not been available twenty years ago. Searching through valve gears had always been a tedious and difficult task, but there would now be available in the Proceedings of the Institution a very concise and convenient history of the development of valve gears. The earlier valve gears were efforts, he thought, to· find a practical form of gear, and from the late 'eighties [1880s] it might be said
As a matter of interest, he had compared the valve events of the first "austerity" engine built on the Southern Railway with those of the second "austerity" locomotive, produced by the Ministry of Supply. The Southern Railway engine used the Stephenson gear; the Ministry of Supply used the Walschaerts. When one looked at the figures, one had to admit that it was quite immaterial whether one used the one or the other; the events' were both good, both engines did the work for which they were designed, and both stood up to their job. The Stephenson gear did not cause any trouble with lubrication. It was piston ring trouble rather than gear trouble which was generally experienced.
Going through the Paper, he could not help thinking of the past. He could just remember the engine on the G.N.R. which was fitted with the Marshall gear. He had been a youngster then, and at Doncaster they were all very interested in the engine fitted with this new contraption. Why it was taken off' he did not know; it was probably a case of " Here's a foreigner; kill it! "
The next gem: which amused him was the Cossart gear on the Nord Railway of France, which was not-mentioned in the Paper. On one occasion when he happened to be in the Nord railway offices, he asked why anyone ever invented that gear, and the answer was amusing. It appeared that the Nord never found it necessary to borrow ideas from other people, and. so M. Cossart was ordered, he believed by Baron Rothschild, to invent a valve gear. To maintain the tradition of not copying. anything used anywhere else, therefore, the Cossart valve gear was evolved, and it was a very good valve gear. On one occasion Sir Nigel Gresley, who at one time had an unfortunate reputation in France they called him the " Jonah," because whenever he travelled by the boat train from Calais it was almost certain that something would happen between Calais and Paris, and they even went so far as to suggest that they would prefer him to travel via Le Havre was on the train and the engine failed at Creil, and the train had to be taken on to Paris by an 8-coupled tank engine fitted with the Cossart gear. He was very surprised to run into Paris behind this suburban tank engine at about two minutes under the normal time with a Pacific, and after that he was very interested in the Cossart gear, its performance having been rather startling.
Everyone was interested in the poppet gears, but they did not seem to have got as far as they should. They were certainly attractive, but there seemed to be something about them which prevented them making progress; what it was he did not pretend to know.
1944, 34, 260.
Corrections and additions were publshed in Journal 179 (p. 260); on page 379 it had been stated that Forrester locomotive of 1832 for the Liverpool & Manchester Railway Swiftsure had four fixed eccentrics, but it appears that it had Carmichael valve gear with one fixed eccentric (Loco. Rly Carr. Rev., 1934 January). The locomotive Vauxhall of 1834 for the Dublin & Kingstown Railway had a four-fixed eccentric gear (Engineer, 1983, 2 March). On page 401 comment on introduction of Walschaerts into Britain failed to note Fairlie-type locomotive built by Yorkshire Engine Co. in 1873 so fitted: locomotive sold to East & West Junction Railway (later Stratford-on-Avon and Midland Junction Railway): illustrated Loco. Rly Carr. Wagon Rev., 1911, Nov.). Another date claim (p. 403) concerned "last locomotive" built with Allan Straight Link Motion as being Dubs locomotive for Highland Railway in 1917, but Yorkshire Engine Co. built two 0-6-0s so-fitted for Maryport & Carlisle Railway in 1921. Additions: Younghusband valve gear tried on five NER passenger locomotives in 1897. Riekie valve gear (a modified version of Walschaerts gear) was tried on Caledonian Railway by McIntosh (illustrated in Paper 194)
E. S. Cox (456-): One cannot but marvel at the ingenuity displayed over the past 100 years in the devising of nearly as many different forms of locomotive valve gears. Leaving on one side the older types no longer in use, even the more modern existing forms are subjected to numerous variations, most of which seem to have been prompted by a theoretical rather than a practical approach. Any of the basic modern valve gears, Stephenson, Walschaerts or cam-driven poppet valve gear can be made to produce effective and economical steam, distribution, granted correctly designed ports and passages, steam tight valves, and selection of the right valve events. While on paper it is possible to split hairs on the relative advantages of these gears from the distribution point of view, when fitted to engines and in daily service, 'no one is distin- guishable above the others. As an example, the G.W. have produced long lap valve events with Stephenson gear, and it would be a bold man who could claim that a Hall class engine so fitted was more or less effective by virtue of its valve gear than an L.M.S. Class 5, mixed traffic engine with Walschaerts gear. Then again, there are a number of examples of the same class of engine fitted with both Walschaerts and poppet valve gears. Where the old gear did not allow the steam to be used expansively and gave rise to undue compression, and where the poppet gear was associated with improved passages and valve events, the latter, of course, showed up well. But where conditions are comparable no such clear advantage is to be seen. Most careful dynamometer car tests were made with the L.M.S. Standard 2-6-0 engines so fitted, and no difference in coal or water consumption could be discerned. Although both versions of this engine continue in active service there is still absolutely nothing to distinguish between them in this respect.
This verdict applies, of course, only to our present normal methods of designing and working engines. Where future accelerations demand super-power outputs. in conjunction with higher steam temperatures and pressures, then the finer points of distribution come into their own and tests on stationary plant may indicate a clear advantage of one gear over the other. But that is of the future so far as this country is concerned and for the present the case is, to say the least of it, not proven.
The most important present factor is, therefore, that 'of maintenance, and on this basis the Walschaerts gear is outstanding. There are 11 points of wear on an outside gear, all but two, those between curved link and block, and between valve rod and lifting block, being simple pin and bush assemblies. Moreover the arrangement of the leverages on this gear is such that cumulative wear at all but one of the pins is actually reduced in magnitude by the time it reaches the valve itself. This gives the great practical advantage that a really run down gear only affects the distribution in a relatively small degree.
Few parts of the locomotive give so little trouble in service or are so cheap and easy to repair as the Walschaerts valve gear. Changing a few bushes and a pin or two at each 50,000-60,000 mile shop repair is all that is required, while re-grinding of the curved and valve rod links is rarely necessary under 250,000 miles. In an endeavour to .reduce even this small amount of maintenance, needle roller bearings have been recently introduced. They have not, however, so far produced any improved results because of the very difficult problem of sealing them against water and dust, within the small dimensional clearances which are possible.
It is just because the straightforward Walschaerts gear is so good that one marvels at the continuous efforts to supplant it, and far more effort and ingenuity seems to be exerted in this direction than towards other items of locomotive design which give infinitely more trouble, such, for example, as cracked plate frames and hot coupled axle boxes.
Reference is made in the Paper to conjugated gears for operating the inside cylinder of a 3-cylinder engine. The best known of these adds 8 pin joints to the existing two outside gears as against 8 pin joints plus two sets of sliding surfaces plus one eccentric if a full third Walschaerts gear had been employed. But a few lines set out on paper will show that the leverage of the 2 to 1 arrangement is such that a wear of x inches at the pins attached to the outside valve spindles becomes 3x 'inches of lost motion by the time the inside valve is reached and in addition, in the more usual form with the 2 to 1 levers in front of the cylinders expansion of the valve spindle where it passes through the steam chests is also multiplied by 3 by the time the conjugated motion reaches the centre valve. From a practical point of view, therefore, there is little which can be said in favour of such an arrangement. Where it involves some 14 pin bearings, as in the Caledonian Railway arrangement shown in Fig. 93, it ceases to be a practical proposition at all, and the four engines so fitted were notably unsuccessful. Tendency all over the world is to give 3-cylinder engines three independent gears.
C.F. Dendy Marshall (458) wrote to say that the story about Humphrey Potter on Page 371 was now disbelieved by competent historians. See Dickinson's Short History of the Steam Engine (1939), p. 41. Page 392. It is quite true that American writers claim the invention of the link motion for W. T. James in 1832. But it may be added that there is no satisfactory contemporary evidence to support the claim. Page 408. Hackworth valve gear.
For many years he had been of the opinion that a form of that gear, properly designed, was most suitable for locomotives: But very few people fully understood it. Except on some agricultural engines, the eccentric rod had always been guided either by a radius rod, the length -of which would be limited by considerations of space, or by a block with a straight slot. By employing a curved slot (the radius of which was much too long for a radius rod), the serious irregularities of the gear could be almost completely eliminated. These irregularities in its ordinary form were so great that marine engines fitted with it had even been made with double ports at one end of the cylinder in an attempt to cope with the situation. They were due to the obliquity of the eccentric rod, which was at a maximum jn full gear and practically vanished in central gear, and to that of the rod running to the valve, which was very nearly the same in all gears. The irregularities in the distribution of all the gears of this type which had so far appeared were mainly due to the fact that the eccentric rod lay at right angles to the central line of the engine, and therefore had to be very short. In The Engineer for 20 June 1913, he published a description and full analysis of a gear with the eccentric rod lying along the' engine, at an angle of about 10° below the horizontal, with the end (beyond the block) connected to a bell crank, the other arm of which drove the valve. The eccentric rod was 7 feet long, which made its obliquity negligible; only leaving that of the link to the bell crank to be dealt with, which was done by curving the slot in the block to a radius of 3 ft. 6 ins. The arrangement was not altogether unlike that used afterwards in the Southern valve gear (Fig. 78), but in that case a radius rod was used, which could not be made long enough to give the required correction. An attempt was made in that direction by altering the angle of the bell crank from its natural value, but that expedient was only a palliative.
A few months ago it was stated in an article in the Railway Magazine that Engine No. 1850 on the Southern Railway was fitted with his valve gear, which was unsuccessful and was removed. The truth of the matter was that the gear tried on that engine was the invention of another Mr. Marshall.
Page 431. He asked to be allowed to add a short supplement to Mr. Shield's reference to his 4-cylinder system. It was far from being the failure that it might have been inferred to be from the fact that it was only used once. The Prospero, originally built in 1907, ran for many years after having been converted to his system in 1915, without alteration. A report from the company, dated August, 1920, gave the coal consumption as 62.7 lb. per mile, and the average 'mileage between repairs in shops as 58,365; whereas the average figures for 49 similar engines not converted was 68.1 and 46,666. (Incidentally, there was an argument in favour of 4- cylinder engines.) Nevertheless, after the death of Mr. Bowen Cooke, the authorities decided not to give the system another trial.
Author's reply. 459
With reference. to remarks of Mr. Marten, he agreed that there was
room for greater research being made with valve gears. Unfortunately his
own practical experience was confined to Stephenson, Allan and Walschaerts
gears. He also agreed with the President that working to fine limits in
locomotive motion construction was asking for trouble; clearances on moving
parts required to be ample to avoid heating.
In actual operation there was little difference between the Stephenson and Allan gears; both did their work satisfactorily and gave little or no trouble., Lt.-Col. Cantlie remarked on the reasons that the various gears were not perpetuated. Each new gear in Its turn claimed some improvement over preceding gears, a claim that was generally not upheld in actual practice. To keep the Paper within reasonable limits only the transition from one gear to another was followed. The step from the early tappet gear to the loose reversing eccentric was a big advance in its time. The chief rival of the loose eccentric being the double-ended lever using one fixed eccentric. The coming of the double eccentric gab motion followed by the introduction of valve lap proved another advance in steam distribution. Shortly before the advent of the link motion the separate cut-off valve still further economised the steam consumption, however, at least in this country, the link motion superseded separate expansion or cut-off valves. Mr. H. Holcroft mentioned the advantages of the Stephenson gear. It has been claimed that the Walschaerts gear with its constant lead was a benefit. However, he was inclined to favour the Stephenson gear WIth its increasing lead toward mid-gear. A locomotive with a large amount of lead in full-gear was tardy at starting, and with the .Walschaerts gear a satisfactory lead must be fixed upon to. suit running conditions. The impetus to the Walschaerts gear since the first decade. of the present century had been chiefly due to structural considerations and the necessity of employing large eccentrics with Stephenson's gear, to operate modern long travel piston valves.
In reply to Mr. A. J. L. Winchester, the best steam distribution, in his opinion, would be that giving the nearest approximate to the theoretical indicator diagram. That would necessitate °a valve motion giving quick admission and cut-off in addition to full port opening from point of release to a constant point of compression. No reciprocating valve motion had yet attained that end. The modern poppet valve gears with only the events of admission and expansion variable and independent exhaust valve 'events was a move towards that ideal.
The President asked why the valve ellipse of the Baker gear was given in the Paper to the exclusion of all others; that was due to t hc Baker gear, as illustrated, being the most recent gear built in this country to which the valve ellipse was available. As regards the modern piston valve, that gave little trouble, and with proper attention to lubrication, engines usually ran between shopping periods without attention, running from 50,000 to 70,000 miles. In reply to Mr. Dendy Marshall, the legend of Humphrey Potter was as probably untrue as otherwise, nevertheless one would like to believe the story of the boy playing on the engine room floor, while his engine was faithfully performing its duty with its sticks and strings, the valves opening and closing by the automatic action of engine, giving the first valve motion.
Mr. E. S. ·Cox referred to the elasticity of the levers in the conjugate valve gear applied to the inside cylinder of 3-cylinder locomotives. Trouble was experienced with the valve motion a given in Fig. 93, and subsequently a dash pot, as shown in Fig. 102,