476 JOURSAL 01’ THE ISBT. OF LOCO. EXGIXEERR
THREE-CYLINDERLOCOMOTIVES,
Pnjer lY171i before the Iiislitirtioti, Londoti, b~ 11. HOLCROFT, McviiJer, Xozwnber 2114 19 18. Contitruaircc oj‘ Discussion at Leecis Centre, Ilecelnhcr 17/li9 1918, Mi.. T. H. Hrocklebnnk /wrsiiiiti<.
PAPER No. 65A. The Chairmail (Mr. T. H. Brtxklebank) : The Hon, Secretary has received several letters of regret tor absence from some of the members. and I will asl: him to read them to you. The Hon. Secretary : As time is rather short, gentlemen, and we want a good discussion on hlr. Holcroft’s Paper, I just propose to tell you Mr. Gresley not only wrote, but alm telephoned me, I was to givc his personal regrets to Mr. Holcroft that he could not be present. Mr. Stamer also wrote again this morning, and I have received letters of rt gret from Mr. Goodall and several other members ; Coloncl Kitson-Clark was sorry hc could not attend, as he had to be in London. The Chairman: One of the great points of a three- cylinder engine is its good starting effort, or “ torque,” as our good French .4llies havc it. One might add that it can ‘. torque ” for itself, but of course we shall all prefer to hear Mr. Holcroft talk for it. I will therefore now ask Mr. Holcroft to present to us his Paper on the threecylinder locomotive, and so makc ‘‘ a good start.” Mr. Holcroft : Mr. Chairman and Gentlemen. Ikfore reading the Paper I should like to be permitted to make a personal explanation. I havc not been actually connected with locomotive work for some years, and for this reason cannot attempt to give you any details of existing. three- cylinder engines and their work, but hope to interest you ii the subject from an entirely novel point of view. A few years ago I made some investigations on three- cylinder locomotives, more especially as to the means of working three valves by means of tn.0 valvc-gears, but hitherto nothing has been published on the subject. The- Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 Tl€REI<-CYI,IST)l rccent appearance of Mr. Gresley’s engine has fixed attentioti on the matter, and great interest has been created, so that the moment was opportune to present the theoretical side for discussion. I received an invitation from the Council in London to give a Paper on the subject, and this I will now proceed to rend to you. klr. Holcroft then read his Paper, which is published in Journal So. 35? Vol. \TllI., of the J’rocecdings. DISCUSSION. The Chairman : IVc have heard Mr. Holcroft’s excellent Paper with great interest, I am sure, and I have much pleasure in congratulating him on it and also on the manner in which he has prcsmted it. Mr. Warren has spcxially come from Darlington to help in the discussion, and has to leave soon by train, so I will ask him to make any remarks he wish-’%s to now. Mr. J. G. H. Warren: Hefore I m;\k<, n fen criticisms I sh6uld like to call attention to a Papcr published in 1913. It was read by Mr. J. Snowden I3elI bef’ore the American Master Mechan‘ics, and deals with the whole subject of three-cylinder locomotives, particularly with the question of the third valve-gear. A description is also given of a valve- gear proposed by Mr. H. S. Vincent, of the American Locomotive Company, who had apparently been working independently at the problem to which Mr. I-Iolcroft has given so much attention. I very much regret that in the time at my disposal it has been impossiblc to give to Mr. Holcroft’s estraordinarily interesting Paper the study which it deserves, but I havc noticed one or two points which seem to call for partic-ular comment. My criticisms or expressions of opinicn must bc taken as expressing only my own personal views. With Mr. Holcroft’s genera1 deductions and plea for an extended use of the thrce-cslinder locomotive I am in com- plete agreement. Rlr. Holcroft’s Paper refers at some length to the latest development of three-cylinder design in this country as sho\vn by thc, ncu‘ 2-8-0 type locomotive of the Great Northern Kailway, and it would be interesting to hear from him whether he considers that the lines on which this pzirticular locomotive has been developed are sound. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 478 JOVH?iAL OF THE ISST. OF LOCO. ESGINEERS. .4 glance at the engine itself sho\vs that the arrangement of the outside cylinders is unusual, 2nd I cannot discover from the published drawings any c-onvincing reason for the adoption of a cylinder arrangemciit tending to produce disturbancx in running, and, I think, loss of efkiciency due to increased friction, and large increases in driving-wheel pressure at the rail. It appears to me, in fact, that some of the advantages which might have been obtained by the use of three cylinders have been lost. On :I first study of the published drawings of the cylinder and valve motion arrangement of this engine it appeared to nie that the placing of the three cylinders in line and on the same incline might ha\.e been necessary in order .to obtain the arrangement for dri\-ing the inside valve by connections from the outside gears. Iht Mr. Holcroft, who has evidently given much thought to this question, has made it clear to us to-night that it would be possible to drive the inside valve from the outside gears rven were the outside cylinders arranged horizontally, as shown by Fig. 13, that in fact with such an arrangement of outside cylinders the valve-gears as a whole would have been simpler than as actually adopted on the Great Northern engine and illustrated by Fig. I. I suggest that undue emphasis has been given to the supposed disadvantages of a third independent valve-gear. It would appear from examination of Fig. XI that the addi- tional parts introduced between points A and B the valve radius rod pins for the outside valves are nearly as many as would be required for an additional independent gear. ,. 1he arrangement adopted also necessitates the use of rocking shafts, which are referred to by Mr. Holcroft as complica tions. Mr. Holcroft’s Paper as a wholc is of such interest that it is likely to lead to considcrahle discussion, and I therefore do not feel justified in touching upon othcr points of interest, but would add that in connection \vith thc particular points to which I rcfer 1 had prepared, some time ago, diagrams to show the relative amounts of certain vertical disturbing pressures at slow speeds and late cut-offs in locomotives ot the 2-84 type and of the same cylinder capacity, but baving- (a) Two inside cylinders of large diameter inclined at I in 8 and with drive on to the second axle. (h) Two outside cylinders of the same diameter placed horizontally with drive 011 to the third axle. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 THREE-CYI,ISDI {c) Three cylinders of total piston area approximately equivalent to zbove, all inclined :it 1 in 8 and with drive OII to the second axle, :IS in the case of the Great Northern engine. (d) Three cylinders as above, the inside one inclined at I in 8 with drive on to the second axle, the two outside horizontal with drive on to the third axle. It is evident that as the result of the incline and drive from the outside cylinders the detrimental tendencies due to upward pressures at cylinder head and slidebar will be greatest in the case of (c). In view of the necessity of obtaining from locomotives of given weight a maximum of efficiency, these particular points appear worthy of fuller consideration. Before I sit down 1 should likc, to save time, to antici- pate some possible objections to my criticisms. I have personally discussed these points with other locomotive engineers and have so far only come across two in favour of the arrangement adopted in the Great Northern engine, and the four principal araiiments used against me are as follow :- Firstly, that the new engine runs more steadily than its two-cylinder predecessor. This may well be the case. I believe the advantages of a three-cylinder engine are so considerable that the three-cylinder , even with this inclined outside cylinder arrangement, is better than a two-cylinder. This argument does not answer my criticism, because I am comparing one three-cylinder engine with another. Secondly, that thousands of engines are running in this country with inside cylinders inclined at I in 8. The fact that they have inside cylinders vitiates this argument. Thirdly, that owing to the weight of the Great Northern engine, the disturbances in running are not evident. This may be the case, but even if the disturbances are not evident the reactions will be there, none the less, although they are not seen. Fourthly, that I am right in theory, but that in practice it doesn’t matter.’’ I submit that sound theory is the -best basis for good design, and that this is a dangerous argument to use. It seems to me that this argument is quite inconsistent with the demand for every ounce of work from every ton of weight, to get which all causes tending to produce disturbance and friction must be eliminated. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 480 JOURNAli OF THE: INYT. OF MCO. ENGINEERS. Mr. S. W. Groom (G.X. Icly., Doncaster) : Mr. Chair- man, Mr. Grcsley spoke to me to-day about the I’apcr to be read to-night, and he was very disappointed at not being able to attend himself to hear it. He handed me his notes and asked me if I jvoulti be good enough to read them, which I will proceed to do. They are somcwhat lengthy, as he is greatly interested in the subject 01 three-cylindcr engines, having recently built one on such lines that he can get a favourable comparison with a two-cylinder engine, every detail of the two engines heing exactly similar, with the exception, of course, of the cylinders. Mr. Gresley \note as follows :- I regret very much that I am unable to be present at the hleeting of the Institution at which Mr. Holcroft’s Paper on “ Three-Cylinder Locomotives ” is to be read and dis- cussed. RIr. Holrroft has already read thc Papcr before the Institution in London, and I suggested to our Hon. Secretary that he should be invited to read it in Leeds. I felt that as tllrce-cylinder engines had been adopted to such an extent by railwavs serving this district a valuable discussion might be expected from our members n-ho havv actual experience uith this class of engine. blr. Holcroft has e\-idently made a dose study of the three-cylinder engine, and has pointed out its advantages in a \cry able and effective manner. With the ever-increasing demands for power in the locomotive, I came to the conclusion some years ago that i: would bc desirable to adopt more than two cylinders. The three-cylinder arrangement ga1.e such advantages over four cylinders that Sir Vincent Raven boldly adopted it, notwithstanding the extra set of valve-gear. I felt that if this disadvantage could be obviated the only point which can be claimed in favour of the four-cylinder :irrangement would be eliminated. By an entirely different method from that described by h1r. Holcroft I devised an arrangement of two levers by which the valve ot the middle cylinder could be operated from the valve-spindles of the outer cylinders. I submitted the design to Professor Dalby, whom I look upon as being one of the greatest authorities on valve-gears. He was very much interested in the gear, which he believed to be novel, and was kind enough to furnish me with the proof, par- ticulars of which I give below. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 THREE-CYLIXDER LOCOMOTIVES-HOLCROFT. $81 240) CRESLEY VALVE GEAR. Assume that the displacement of the balves is simply harmonic. Let Y be the radius of the equivalent eccentric and let q be the angle which thc equivalent eccentric of the right-hand valve makes with the line of stroke of the valve. Then $I+ 240' is the angle which the left-hand equivalent eccentric makes with the line of stroke of the left valve. Wehave to show that the linkage produces a motion of the point C equa1 to that which would be produced by an equivalent eccentric standing $ + I 20' with the line of stroke of the middle valve and of radius Y Referring to the diagram- The movement of A = movement of right-hand valve- spind.le=r cos $. The movement of B=-& the movement of the left- hand valve-spindle'= -4 cos (+ + 240). The minus sign is introduced because the link EF changes the phase of the motion of the left-hand spindle by 180'. Then movement of C=-r cos 9 about H as centre and -r cos ($+ 240) about A as centre. Total movement of C is therefore -r cos q - (rcos 6 cos 240 -r sin q sin 240) =-rcOsq+4rcos$+rsincpsin 240 = -4 Y cos 9 + r sin $ sin 240 =-I (cos 9 CQS IZO - sin sin 120) =r cos (q+ 120). Q. I;. D. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 482 JOUBSAL OF THE ISST. OF LOCO. ENGINEERS. It was not unti! some TZ months after that I discovered through the Patent Office that Mr. Holcroft had a gear for the same purpose, and that his gear, whilst differing in its arrangement and application, was based fundamentally on the same principle as mine. I consider, therefore, that to Mr. Holcroft belongs the credit of having first devised an arrangement by which only two valve-gears are necessary for three-cylinder locomotives. Before applying the gear to a locomotive I set up a full-sized model, from which I was able to obtain curves of the valve events of the outside and insidc cylinders for all points of cut-off. I am sending some of the sheets, which will no doubt be of interest to the Meeting, and which clearly show how closely the movements of the middle vahe approximate to those of the outer valve. I am also sending a drawing showing the generar arrangement of the gear as applied to a 2-8-0 coal engine. My original arrangement, which I have so far not applied to an engine, is that shoan by hlr. Holcroft on Fig. 9. Having some very powerful two-cylinder coal engines of the 2-8-0 type already at work on the Great Northern, 1 decided to build a three-cylinder engine which would he otherwise identical in every way with the two-cylinder engine. 'The boiler and wheel arrangement, tractive power, adhesive weight, etc., wcre the sanic in both engines. I realised that the tractive power might ha\ c: been increased with advantage by the use of slightly larger cylinders, but this would have spoilt the tests for comparative purposes. f considered that if thc three-c-1 linder engine proved in actual working to be better than the tua-cylinder on equal terms, that the success of this type would be assured when advan- tage was taken of the increased tractive effort which can be obtained with the same adhesive weight. 'The following table gives the leading dimensions of thc engines tested, from whidi it will bc seen that they are about the most powerful engines at work in this country :- Two-cylinder engine. Three-cylinder engine- Cylinders ...... 21 dia. x 28'stroke. 18' dia. x 26" stroke. Boiler hcating surface ... 1,927 square feet. 1.927 square feet, Eleineiits ,Superhcatcrl ... 430.5 ,, ,, 430.5 ,. ,, Firebox 163.5 ...... - ,, ,, -163.5 Y I Totxl ...... 2.521 *. .. 2.521 ~ .. Grate area ...... 27.5 ., .. 27.5 v $3 Boiler pressure ...... 17olbs. per sq. in. 17olbs. per sq. in- Total weiglit (A engine ... 76 tons, j cwt. 76 tons, s cwt. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 The engines were designed for working wal trafiic between Peterborough and London. Their regular working. load is 80 10-ton coal \vagons and a zo-ton brake, the total \vcight behind the tender being approximately I ,300 tons. Mr. Churchward wis kind enough to lend me the Great IYestern Dynamometer Car, and trials were made with both er?gines. Sections of the charts obtained are shown, which clearly indicate the steadier pull given by the three-cylinder engine. The tuo-cylinder c:ngines were built up in 1913 and thc three-cylinder was sent into traffic last May. Up to date the latter engine has run just over zo,ooo miles. There is a good dcal to be said for the design shown on Fig. 13, in which the outside cylinders ;it-(: horizontal and the inside cylinder inclined, but I do not like the off- setting of valve-spindles of the outside cylinders which is shown in detail in Fig. 6. A little consideration will show that the forces actuating the outside valve and the rocking lever for inside valve :ire not always constant in the propor- tion of z to I. There :IIY periods when the inside valve is practicdly stationary and both outside valves are moving in one direction and the. other in the opposite direction, the result being that the flo:itiny: lever is only moving pivotally about its centre. At surh moments the off-set of the valye- spindle cannot he corrrc‘t, and will result in :i side thrust being given to the vah.e-spindle. Although my original scheme of two horizontal levers only as shown on Fig. 51 is so extremely simple, it is by no means easy to work it in on the back side of the cylinders; the valve motion of thc outside cylinders, the nhecls and the slidebars of the middle cylinder have to be avoided. In fa(-t, it appears that the simplest method of applying it is to fit the levers on the front of the cylinders and connert them to the valve-spindle tail-ends. I have had an opportunity of reading 3rr. 11:arren’s criticisms of the Great Sorthern three-cylinder engine. The chief objection raised is the effect of the inclination of the outside cylinders. It is contcnded that this ivill cause- (I) Vertical disturbance and rolling. (2) Increased friction. (3) Increased nsle loads. Some time ago I obtained a hIuni-n Recorder, n very sensitive and beautiful picce of mechanism for recording Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 484 JOVRNAL OF THE 1SST. OF LOCO. ESUTNEERS. vertical and lateral oscillations, and which I have found very usefril for testing the riding of dining-cars and other carriages. I fixed this Recorder on the outside framing over the cylinders of the two and three-cylinder coal engines and .obtained comparable records at the same speeds over the same section of the line, and with similar loads. I also got charts with the Recorder fixed on the centre of the buffer beam. I am sending the original records which were obtained, and regret that I have not had time to malie a large-scale reproduction. These records show that at the slowest speed there is slightly more vertical movement in the three-cylinder engine, but that at the normal running speeds they are less than with the two-cylinder. They show further that as compared with the lateral movement the vertical is negligible and that at all speeds the three-cylinder engine is a steadier- running engine than the two-cylinder ; in fact, the diagrams only confirm the actual observations of anyone who has ridden on the two engines. Mr. Warren also anticipates increased friction. In- creased friction would either result in less hauling capacity or increased coal consumption. The hauling capacity of the engines is the same. The loads they haul are equal and are the maximum that they can deal with. If the loads were increased from 80 to 85 wagons they would never start the trains on a curve with a rising gradient of I in zoo, as they have to every day. The coal consumption of the three-cylinder engine has consistently been several pounds per mile lighter than thc two-cylinder engines ever burnt, and this I think disposes of the criticism of increased friction. I have dealt at some length with Mr. Warren's criticisms as he has been to some trouble to back them up by diagrams and calculations. His objections, however, are not sub- stantiated by actual results. I think Mr. Holcroft will agree that if satisfactory results can be obtained by a three-cylinder engine having so many imperfections as the Great Sorthern engine, there is a great future for a three-cylinder engine in which thesc defects are eliminated. The Chairman: It would bc interesting to mention that a three-cylinder locomotive built by Icobert Stephenson 8. Co. was put into service in 1852 on the York, Newcastle 8: Berwick Railway. It was a 2-2-2 express locomotive. The outside cylinders were Ioiin. diameter by 22in. stroke and the inside cylinder was 168in. diameter by 18ir1. stroke. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 It seems strange that with all the manifest advantages appertaining to the threecylinder engine so few examples are to be found in railway practice. In all my long ex- perience of designing locomotives we have never at our works constructed one of the three-cylinder ty,pe. In 1906 some engines of this type werc suggested by Mr. F. W. Rach (,who in 1910read a Paper in which he advocated their use to the members of the Institution of Civil Engineers) and constructed by the Xorth British Loco- motive Co. for the Central Railway of Peru, but whether others of the same class have been built I am not aware. There are, as Mr. Holcroft has stated, numbers of three-cylinder IocomDtives in service on the North-Eastern Railway, one of which is fitted nith Stgmpff cylinders. Possibly if there are any gentlemen here to-night repre- senting the Korth-ISastern Railway they might kindly give us some of their experience of the results in service. Mr. Gresley, our worthy Chairman, has recently intro- duced, as stated in the Paper, sonil: three-cylinder loro- motives of the 2-8-0 type on the Great Northern Railway, and has been good enough to send to-night some very valuable notes regarding them. At the time Mr. Bach suggested thc three-cylinder engine for the Peruvian Railway we investigated at our works the turning efforts of the two-, three-, and four-cylinder engines. We found that taking the masimum turning effort .at IOO the two- and the four-cylinder engines fel! to a mini- mum of about 64 per rent. and the thi-t.e-cylinder en&'rines to a minimum of about 7j per cent. Notwithstanding t-he above, it is strange to think that at the time all the designs of the Indian Standard Engines were considered (with which I was cmwerned), to the best of my recollections, no suggestions \\.('re made of any other type than the two-cylinder engine, and cvxtainly no other has been adopted. The three-cylinder engine, with all its advantages, of course has its limitations, such as, for instance, in designing a 10-wheels coupled locomotive, it \\.as found that three cylinders, owing to limitations of gauge for the outside cylinders, could not be made large enough to give the necessary traction, and four cylinders were arranged for. As regards the valve-gear for the three- and four-cylinder engine it is possible, as mentioned by Mr. Holcroft, and allowable to use two sets of valve-gear in each case, but to Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 486 JOURNAL OF THE INRT. OF LOCO. ENGINEERS. my mind the small saving in parts effected does not seem very appreciable, and certainly the most effective steam distribution is secured by the use of thrce or four sets of valve-gears as required. There is one great advantage the four-cylinder engine possesses over the threecylinder, and that is in thc much. better balancing of the reciprocating parts in the former over that of the latter. In conclusion, I would add that possibly after considera- tion of Mr. Holcroft's Paper by railway locomotive engineers more locomotives of the three-cylinder type may be con- structed. Mr. H. A. Akroyd (The Yorkshire Engine Co., Sheffield): The Author mentions that it is agreed that a four-cylinder engine with two valve-gears also has marked advantages, and is actually simpler than the three-cylinder with three valve-gears. He did not mention that it is further possible to design the four-cvlindcr type with only two slide- valves, thus allowing this portion of the mechanism to be practically as simple as a two-cylinder engine. The valve- gear can thus be made far simpler than any known design of three-cylinder engine. It does not appear to me that anything has been saved by the elimination of one valve-gear in the drawings shown, as the number of wearing points is actually greater than before, unless the Author has in mind the inside eccentric, which is not an essential feature even of inside W'alschaert motion. Turning to the advantages of the threecylinder system, the first claim is superior starticg. In this particular there is very little difference between the four-cylinder and three- cylinder. The ratios of maximum to mean crank effort at starting are respectively for two-, three-, and four-cylinders, I .25, 1.065, and 1.1 to I, thus requiring for the same tractive. effort adhesive weights in the ratio of I, .852, and .88;in the last two cases there is thus very little difference. At higher speeds, however, the margin in favour of the three- cylinder system is more pronounced, but this is offset by the adhesion being more than sufficient in any case under these conditions, if the action of the balance-weights be neglected particularly. As in four-cylinder engines, the reciprocating weights do not require to be balanced, there is no tendency for the ueight on either side of the engine to be relieved. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 THREE- GY I,I S I)ER LOCOJIOTI\T S-HO LCROFT . 487 I think, therefore, taking into consideration that the Sourcylinder engine can he designed with simpler valve-gear and that the characteristics arc so nearly equal, the case is for the four-cylindcr, if and when the prevailing two-cylinder engine is to be superseded. Mr. Holcroft: Mr. Chairman and Gentlemen. I have to reply to a number of interesting points raised in the discussion. Mr. Warren asks my opinion of the cylinder arrange- mtnt in the 2-84 engine on the Great Northern Railway, as there has been a good deal of criticism of it and a number .ofpeople seem to think that the inclination of the cylinders is excessive and detrimcntal. In reply to this I wish to point out that the London & Sorth-U’estern Railway have had a number of ,hsth three- and four-cylinder compounds of the 0-8-0 type, and in the latter case 2-8-0 type as well, with .steeply inclined outside cvlinders. These engines have been running for a number of years, but there does not appear to have hecn any criticism of them. Of course the speed of the engine will have a great deal to do with the objection to the outside cylinders being inclined. In the case of a coal engine running nornialiy at 12 or 15 miles an hour no detrimental effect is observed, but the design would he unsuited for higher speeds. Theoretically there does seem to be some objection to an inclination of I in 8 for outside cylinders, but practically there does not seem to be much in it at any rate at slow speeds. Mr. Groom 1-cad wme very interesting remarks from Mr. Gresley, in which the off-set shown in the diagrams is referred to. It is true that while the average forces are balanced, the actual forccs at any moment may be slightly out of balamx, but the nmount is small, and in the diagrams the off-set is exaggerated for clearness, and, in addition, the zeccssary guide for the \.alve-spindle crosshead is omitted. In the case of the Sortli Eastern engines the inside valve- gear and valve-spindlc are off-set about gin. without any bala.nce at all, and the :irrangement appears to give no trouble . As Mr. Gresley points out, there is some difficulty in using the simple form of the gear. If it is put at the front of the engine the gear has to be disconnected every time an examination of the valws is made. Also therc is trouble from the expansion by heat of the valve-spindles, but this can, of course, he allowed for. In the case of the London 81 North Western Rnil\my four-cylinder compounds, where the Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 488 JOVRSAL 01.' TIIK ISSl. OF LOCO. ESGISEEHS. outside valves were drivc:n irom the spindles of the inside valves the former \vere affected by the expansion of both spindles, and the same sort of thing would apply to a three-cylinder engine \dIi the gvar in 'front. I am very plrased our Chairman anticipates :I multi- plication of three-cylinder engines. I am sure once the advantages arc widlely realised these engines will become more general. I have not seen the Paper read by Mr. Snowden IJell in .imerica, although I am alvare of Mr. H. S. Vincent's arrangements for working three valves with two gears. Mr. Akroyd refers to the four-cylinder system in which tu-o valves arc: operated by two valve-gears, there being a single piston-valve to each pair of cylinders. While this is a simple arrangement, it is open to the objection that the steam distribution is not thc same in each of the cylinders and no independent adjustmcwts can be inadc. In the case of the Great Western I thanks to Mr. Holcroft for the very interesting and attractive Paper wc have listened to. If one may judge a Paper on the amount of discussion it has been a very good one. I am sure we are all 1m-y pleased, and feel that we have greatly benefited by it. Mr. J. W. Kidd: I have much pleasure in seconding that motion, and I an1 sure that if the Paper has given the other members as much pleasure as it has given me, Mr. Holcroft's visit to Leeds will not have been in vain. The vote of thanks was carried unanimously. COMMUNICATION. Mr. J. J. Weatherburn (S.E. Rly., Darlington) : It has given me much pleasure to read the above Paper, as it c,onfirms the opinion of the Chief Alechaniral Engineer of the Sorth Eastern Railway that this type of engine is the ,most suitable for general rail\vay work. .\t the present time the thrtvcylinder engine is the stantlard express cngine on the North Eastern Railway, and also the standard I~uiking-engint:. Some mineral tank and some passenger tank etigincs of the three-cylinder type are also in use. *.ihese engines hav(! g-iven such satisfactory results that :t :t number of ;argc. goods tender engines are now on order. The boilers, connecting rods, axles, valves, and \-al\.e-g:ear !\.ill be the same on the two classes of engine. The approximation equation to pull and speed curve of the mineral engine will be ?J = 16- 0.25 2 up to a speed in about 20 miles per hour (y=pull in tons and x=speetl in miles per hour). Having watched the \\.orking and tested many of the S.E.R. three-cylinder engines, I am pleased to say that the Author's theoretiail deductions are all confirmed by the practical results obtained. With regard to two sets of valve-gear versus three sets, I think it will be found that the latter will give the best results, as three sets will remain longer in good condition than two sets. It is a well-known fact that coal consumption goes up as soon as the valve-gear gets out of order. There is a double advantage due to the more uniform crank effort. Onc is, that it is the maximum crank Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 .I')o JOURXSAL 01F TEE ISBT.. OF LOCO. ENGINEERS. effort that causes the engine wheels to slip and the minimum crank effort which preyents the engine from starting ; there- fore it follows that a reduction of the difference between minimum and maximum crank effort will tend to reduce slipping and prevent the engine from refusing to start. l'he other advantage is that there is less shock on the working parts of a three-cylinder engine due to its more uniform crank effort, and consequently the wear and tear is less on these parts. H.iL.wciw.-In addition to the advantage mentioned by the Author, the balance-weight to he placed in the driving wheel of a three-cylinder engine is about 30 per cent. less than that required for a two-cylinder engine, so that the lifting force in each wheel due to balaiicing of reciprocating parts is reduced by 30 per cent. The six exhausts per revolution allow the engines to hase the regulator full open when running slowly on heavy gradients, or in starting out of a station without the ill-effect on the fire which occurs \vhcn the same thing is done with a tuo-cylinder engine. ?'he attached diagrams were taken from the blastpipe of a two-cylinder engine; one of them, when going at 60 miles per hour, shows that 71 horse-power is absorbed by the blastpipe. This is one of the factors which causes a reduction of pull as the speed increases. Mr. Holcroft, in reply to Mr. Weatherburn's remarks, said : From Mr. 11-eatherburn's wry interesting remarks it is evident that all the claims put forward in the Paper for three-cylinder engines are actually realised in practice on a11 classes of traffic. Mr. Weatherburn prefers thrcc sets of valve-gear to two, 011 the grounds that the former will remain longer in good condition and that the r-oal consumption goes up as soon as the gear gets out of order. No doubt there is something in this, where the Stephenson link-motion is concerned, as it is not sery accessible and the eccentric straps have to he closed up periodically. With an outside motion, such as the Walschaert gear, the whole of the joints are exposed and can be got at easily. If they are provided with renewable bushes there is no reason why the gear should get out of order at all, as any slacltness.can be taken up quite cheaply directly it appears. If this is provided for any objections as to lost motion at the centre valve 3-ani sh . Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016 THREE-CYLINDER LOCOMOTIVE8-EOLCROFT. 49' There is another point which shou!d not he lost sight of and that is the influence of the third valve-gear on the general design of the engine. It often happens that in order to accommodate the third valve-gear some freedom in general design is lost. The operation of the centre valve from the outside gears removes this restriction, as the necessary rocking levers can be worked into the design where it is impossible to get a full valve-gear, as they take up little space and their actual arrangements can take a variety of forms to suit the circumstances of the case. Downloaded from jil.sagepub.com at CAMBRIDGE UNIV LIBRARY on June 5, 2016