Fry Z+. Fiq: 1. J n Fiq: 18. F. P. L. MA I N t <' i SECTION A A A PLAN POINT-RODJOINT. 2773.. F. P LA N. 4 F. P. L. -iL MAIN t-- Y ELEVATION A A. + SPRINGBALANCER AND LOCKINGBAR. RE L1 F E TELEGRAPHPOLE. M -----t MA1 N t- r- Fz'a: 6 . / +I 1 I L GOODS-LOOPINDICATOR. F7;q: 7. l + INDEPENDENTDISK. B-.. ROUTE-INDICATWR. PLATFORM LINE i MAINLINES t PLATFORM LINE BLOCK DIAGRAM A T. BLACKALL. Downloaded by [ University of Liverpool] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] BLACKALL ON RAILWAY-SIGNALLING. 153 28 February, 1911. ALEXANDERSIEMENS, President, in the Chair. (Paper No. 3931.) “ Railway-Signalling : Developments on the Great Western Railway.” By ALFRED THOMAS BLACHALL,M. Inst. C.E. THE Paper on railway-signals by the late Mr. R. C. Rapier, read at the Institution in 1874,’ described very fully the evolution of rail- way signalling up to that date, and Mr. A. M. Thompson’s Paper on the signalling of the London and North Western Railway, in 1885,2 showed advances madein railway signalling and interlocking during a later period. In the present communication it is proposed to refer to some further developments which have taken place in recent years upon the Great Western Railway, that being the line with which the Authoris connected and best acquainted. Although signalling and interlocking had longbeen an established feature of theGreat Western Railway, there were stillin 1889 many stations and junctions where the signalling was, according to modern ideas, very insufficient, and at which there was little or no attempt to concentrate or interlock the levers. The Regulation of Railways Act passed in that year gave power to the Board of Trade to require railway-companies to set their houses in order in various ways, and amongst the Orders made by the Board of Trade in virtue of thesepowers was onedated the 26thNovember, 1890, which required the Great Western Railway Company to adopt the block system on allits lines, with certain exceptions, andto provide for the interlocking of points and signals, also subject to certain exceptions. Although it was not found possible to comply with these require- mentswithin the actual times specified in the Order, they were fulfilled with all reasonable speed,and within a short time thewhole of the railway had been properly and efficiently signalled. As the Minutes of Proceedings Inst. C.E., vol. xxxviii, p. 142. * Zbid, vol. lxxxii, p. 166. Downloaded by [ University of Liverpool] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. 154 BLACKALL ON RAILWAY-SIGNALLING. winutes of GreatWestern Railway had been extendingand improving its interlocking and signalling arrangements for many years, the effect of the Order was simply to expedite somewhat the completion of that work of signalling its line throughout which the company had already taken in hand, A few years ago, the company, having in mind that the signalling of its railway comprehended something more than the installation of semaphores, the connecting of rail-switches, and the interlocking of levers actuating them, andalso having in mind theextensive and increasing use of electrical appliances in signalling, decided that the co-ordination of the outdoor signalling and block signalling was a necessity ; it therefore placed the supervision of bothsignalling and telegrapharrangements under one control. It maybe of interest to recall that in the discussion on Mr. Thompson’s Paper, Mr. Spagnoletti, then Telegraph Superintendent of the Great Western Railway, advocated this course, and events have proved the correctness of his views. The Signalling Department controls the construction and maintenance of all signalling appliances, both mechanical and electrical, including telegraphs and telephones. The modern developments of signalling on the line arelargely in the direction of the increasinguse of electrical apparatusand appliances in connection with its outdoor signalling arrangements, andthe Author proposes, inter alia, to describe briefly some of these. IXTERLOCKINGFRAMES. For many years an interlocking frame designed by the Author’s predecessor (hisfather) was used, in which the interlocking of levers was carried out in a manner peculiar to the Great Western Railway ; but this form of interlocking could not be applied to conditional or special locking, and was suitable only forthe ordinary locking or releasing of onelever by another. For conditional- interlocking combinations tappet-locking had to be resorted to, and this led the Author to decide to use tappet-locking generally. With the exception of some smallerframes in which the interlocking between the levers is effected by means of what is known as stud- locking-which is reallyamodification of theother method- the tappet form of locking now generally employed on most rail- ways is used. ARRANGEMENTOF SIGNALS. It is of the greatest importance to place the signals so that they shall be easily readand understood by engine-drivers,and in Downloaded by [ University of Liverpool] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] BLACKALL ON RAILWAY-SIGNALLING. 155 Figs. 1-8, Plate 5, is shown the generalplan upon which the signalsare placed with this object in view. It will be seen that the general idea is to place each signal next to and upon the left- hand side of the line to which it applies, and to vary the height of thearms in accordance withthe importance of the lines. For instance, in Figs. 1 and 2 it will be noticed that the home signal at the facing points in each case has the arm for the main line higher than Lhe arm which applies to the branch, and to emphasize the distinction the former is placed upon the main post of the signal, while the arm for the branchis bracketed out. In Fig. 3, where the speed on both of the diverging lines would be the same, neither homesignal is upon the mainpost of the signal, but both are bracketed out to indicate the equal importance of the arms. In Fig. 4, where there is no branch line, but merely a turn-out to an avoiding line or siding, the principle of keeping the main-line arm on the straight post higher than that for the diverging line is again acted upon, and asthe loop line is comparatively unimportant thearm for it is kept lower than it wouldbe for an ordinary branch line, while it is also smaller. The signalling for parallel lines is shown in Fig. 5, where each signal is placed next to and upon the left-hand side of the line to which it applies. A junction at which fast running is on the straight road is shown in Fig. 6, where the speed is low on the branch line which goes off to the right, with a lower speed still upon the branch line going off tothe left, the arms upon the junctionsignal being varied in height accordingly. The signals for a " scissors " crossing in a station through which thereare four linesare illustrated inFig. 7. Theelevation will show how the signals are arranged to make them distinctive. No. 1 is the signal for the through line A, No. 2 is the signal leading from the through line A to the platform-line, No. 3 is the signal leading from the platform-line to the through line A, and No. 4 the signal for the straight platform-line. A double junction between parallel lines is given in Fig. 8, which shows the arrangement of the junction signals. The arrangement is on the same lines as in the othercases mentioned. It happens frequently thatit is not possible to arrange the signals as here described, owing to want of space between the lines, but it is very desirable in preparing plans for new lines or stations, and for other rearrangements of lay-out, to arrange the spaces between the lines so as to allow of the signals beingfixed in their properplaces. Downloaded by [ University of Liverpool] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. 156 BLACKALL ON RAILWAY-SIGNALLING. [Minutes of Signals upon gantries spanning the lines are read very easily by drivers,and can beplaced actuallyover the lines to which they apply. The expense, however, of a signal-gantry is very consider- able, and is hardly to be justified unless its provision is absolutely unavoidable.The disposition of thepoints at very compliated stationsand junctions renders it impossible, inthe majority of cases, to group many signals upon one gantry so that they shall 011 be intheir right places, because it seldom happens that all the facingpoints and fouling points which the signals protect come immediately under the gantry. On this account very few gantries are provided upon the Great Western Railway. It was formerly the practice torepeat the home signals of a junction at the distant, that is to say, each home signal had its corresponding distant, but inview of the fact that atmany junctions there is fast running on one line only, and that a train diverging from the main route must reduce its speed considerably, it was felt to be bad practice to give the same indication upon approaching a junction to a driver who was required to reduce the speed of his trainto, say, 15 or 20 milesper houras to a driver whowas permittedto run through the junction at full speed. It is now customary, therefore, at junctions where there is fast running on one line only to provide but one distant signal, and this signal is capable of beinglowered only when the road is set for the fast- running line. The driver of a train which has to leave this line at the junction, and in consequence to reduce the speed of his train, passes the single distant at danger.This arrangement has the advantage of ensuring that the driver of the train which is required to slacken speed is checked at the distant signal, and it is also an economical arrangement.