m ^'^:- W r;>SHj^: m ^; ^;^H i^'M: 1 ? '.■:: ^'- ^^f i^ ■'! i'^:^-m ^v.,-T /a EXPERIMENTS SHOWING THE AMOUNT OF EFFICIENCY TO BE OBTAINED BY AUTOMATIC YACTJTJl BEAKES. 1882. RAILWAY BRAKES. THE VACUUM PRINCIPLE, STARTLING FACTS. In former pamphlets the Compressed Air system, as illustrated by the Westinghouse Automatic Brake, has been compared with the Automatic Vacuum system, as represented by the Clayton Brake used on the Midland Railway. The present pamphlet contains the results of a very complete series of experiments which have since been carried out with vacuum apparatus, in which great care to ensure accuracy has been taken. These show that the statements already published are more than substantiated, and they also bring to light some further important facts relating to the nature of a vacuum brake, which it is believed will repay a study, and will be read with interest in connection with Colonel Rich's report on the accident which occurred at Port- skewet Pier, on the Monmouthshire branch of the Great Western Railway, on the 25th of April last. For although the experiments referred to have been made with the apparatus in use on the Midland Railway, the conclusions hold good in all essential points for the Great Western brake ; the leak-hole in the piston, which is so strongly animadverted upon by Colonel Rich, being an essential feature in both contrivances. It is one amongst other weaknesses of a vacuum brake, that many of the statements made by its advocates can never be substantiated by actual experiments. Bare assertions, with- out proof, are greatly relied upon. In no instance have the 13 2 professed believers in the automatic vacuum, or non-automatic vacuum principle, shown a desire to strengthen their position by having full and careful experiments made in the presence of their friends and adversaries. On the contrary, they appear to be satisfied to rest their chances for commercial success upon everything except the merits of their apparatus and principle. This is very significant. On the other hand, it is equally signi- ficant that the Westinghouse Brake Company should always have courted the most public tests, and been prepared to go to any expense to prove their statements by figures and diagrams. Before going into particulars, and that a just estimate may be formed of the value of the experiments, a few facts must be borne in mind. 1st. The highest pressure obtainable from a perfect vacuum cannot exceed 15 lbs. per square inch at the mean state of the barometer, and in practice with brakes the vacuum does not average so much as 10 lbs. per square inch. 2nd. The pressure resulting from the compression of air is practically unlimited, and that commonly used for brakes is from 70 to 80 lbs. per square inch for express trains. 3rd. The brake force, or brake-block pressure on the wheels, required, varies according to circumstances, and for express trains, according to Captain Galton's experiments, should not be less than 30,000 lbs. for a carriage weighing 20,000 lbs. 4th. The necessary brake force must be capable of being instantly applied to every wheel of the longest trains that may be run, or at least to twenty-five vehicles. In addition to these points and bearing upon the results which will be given later on, may be mentioned four other equally undoubted facts. (a.) To do a given amount of work, the brake apparatus for the vacuum principle must be at least eight times larger than that for the compressed air principle. O {b.) A much greater volume of air has to be operated upon with large vacuum apparatus, than with the small appa- ratus for compressed air. (c.) A given quantity of air is moved more quickly by a high than by a low pressure. (d.) As a consequence of the three foregoing, it follows that the vacuum brake must be slow in action, and the ap- paratus cumbrous and costly, as compared with a brake operated by compressed air. The experiments referred to have been made with apparatus representing trains of both fifteen, and twenty carriages, fitted with the Clayton brake as used on the Midland Railway. A Clayton cylinder, having the usual leak holes, was so arranged that it could be connected at various parts of the train pipe, and the piston being attached to the recording apparatus, the effective force actually exerted upon the piston, as well as the time required to bring the force into operation in different parts of a train, was automatically registered on an indicator diagram. The system of diagrams was adopted for thi» purpose as being the only safe method of securing reliable particulars, and the apparatus employed was part of that used by Captain Galton for recording the results of his experiments on the London, Brighton, and South Coast Railway. The stroke of the brake piston was 4^ inches (except in the case of a few diagrams, when it was 6 inches), and reservoirs upon each carriage represented the capacity equivalent to the stroke, or to the contents under the piston when the brake was full on. Diagrams i, 2, 3, 4, and 5 area series taken from the 1st, 4th, loth, 14th, and last vehicle of a train of twenty carriages ; the initial vacuum in the cylinder ranging from 24 inches to 10 inches. Diagrams 6, 7, and 8, give the same particulars for the ist, 8th, and last vehicle of a train of fifteen carriages. Diagram 9 shows the single diagram at 20 inches vacuum taken from each of the first series and represented together ; also that from an initial vacuum of 10 inches. Diagram 10 is similar to No. 9, except that the stroke of the piston was 6 inches instead of 4^, and illustrates the large loss of power resulting from an increased stroke. To assist in appreciating the importance of these diagrams, numbers 3 and 7 are translated into figures in Tables I. and II.; these diagrams being chosen because they represent the average work of the brake on trains of twenty, and fifteen vehicles, respectively. The first point which strikes the eye in looking at these diagrams, is the rapidity with which the power (which it has cost so much to produce) is allowed to disappear, as indicated by the slanting direction of the lines. This is of course due to the " patent " hole in the piston, which it is clear does its work very successfully. The dotted line shows what would have resulted with this leak -hole closed, and the heavy black line represents the force required for efi'ective work. The next point which attracts attention, is the diff'erence between the initial degree of vacuum in the reservoir before the diagram was taken, and the degree of vacuum remaining for effective work when the brake was full on : thus from 24 inches it reduces to 16 }4 inches, and from 12 to 3^ inches effective vacuum. Now this is a very important fact, and is the result mainly of the simple movement of the piston in bringing the blocks against the wheels. In other words, a considerable proportion of the power at a high initial vacuum, and the whole of it at a low initial vacuum, is ab- sorbed in doing nothing. This serious defect cannot be prevented in any automatic vacuum brake, owing to the laws which control the expansion of air. Could an absolutely perfect vacuum be obtained, the upward movement of the piston would not reduce the vacuum in the reservoir, but as under no circumstances can anything but a partial vacuum be obtained in practice, the air remaining is compressed, and thus the vacuum is diminished in proportion as the movement of the piston diminishes the capacity of the space above it. With a reservoir of very great size no serious loss would result, but, with the small patented reservoir now employed (the only peculiarity about which appears to be its incapacity for the purpose to be effected), the efficiency of this brake is seriously influenced by the simple stroke of the piston. This stroke may vary from 3|- to 6J inches, depending upon the wear of the brake blocks, pins, &c., and the amount of attention given to the '* taking up " of the blocks. A glance at the following table will show how important are the effects resulting from an increased stroke alone. The reductions of various degrees of initial vacuum at both 4^ and 6% inches stroke, were ascertained from a gauge fitted to the reservoir, and this table is without reference, for the moment, to the effective power illustrated by the diagrams. Initial Reduced Vacuum owing to Stroke of Piston, at Vnrnnm in Inches. 4i inch Stroke. Per centage of Loss. ei inch Stroke. Per centage of Loss. 24 22 8-3 21 12-5 22 19 13-6 175 20-4 20 165 17"5 14-5 27-5 18 14 22-2 11-5 361 16 11-25 29-5 8 50 14 8-5 39-2 5 64*2 12 6 50 25 791 10 3 70 nil 100 It will be seen that while at 24 inches initial vacuum there is a loss of 2 and 3 inches respectively, or say SJ and 12J per cent. ; at 20 a loss of 3|- and 5i, or 17 J and 21^ per cent. ; at 8 12 there is a loss of 6 and 9} inches, or 50 per cent, and 80 per cent, of the initial degrees of vacuum, due solely to the stroke of the piston. This loss of a power, which was sufficiently restricted to begin with, is bad enough ; but, as proved by the diagrams, the result is in reality much worse. This brake is so constructed as to leak off in periods varying from about i min. 40 sees, to 30 sees., from the time of application, according to the degree of initial vacuum. So effective is the contrivance for this purpose, that the power begins to diminish before it has had the oppor- tunity of fully exerting itself. Moreover, the power due to the degree of vacuum in the reservoir above the piston, cannot be exerted until the large space formed below, by the upward movement of the piston, is filled with air. The result of this combination of defective design and principle is that, the effec- tive pressure upon the piston shown on the diagrams, is still less than might be anticipated from an inspection of the figures given on the previous page. As already mentioned the stroke for all the diagrams except the last was 4^^ inches, this being taken as a favourable aver- age, and the following are the figures from the third column of Table I., which is a Iranslation of diagram No. 3 :— Initial Vacuum in Inches. Effective Vacuum in Inches upon piston at 4^ in. stroke. Percentage of Loss. 24 i6-6 30-8 22 14 363 20 11.6 42 18 9'5 47-2 16 7*5 531 14 55 60 12 3*4 73-3 10 i'5 85 The real loss, therefore, at 24 inches is 7^ inches, or 30 per cent. ; at 20 inches it is 8 J inches, or 42 per cent. ; and at 12 there is still a loss of about S}4 inches, or 73 per cent. ; whilst below this point there is scarcely power to bring the blocks against the wheels at all. In column 4 of Table I. will be found the brake-block forces resulting from these pressures, calculated on the effective area of the piston and multiplied by the leverage.* From an initial pressure equivalent to 12 lbs. per square inch down to 6 lbs. there is a reduction in the brake-block force of 15,424 lbs., or a fall from 19,396 lbs. to 3,972 lbs. The actual force result- ing from 24 inches or 12 lbs. pressure being under 20,000 lbs. is less than two-thirds that required for effectively braking a carriage weighing 30,000 lbs., as found by Captain Galton's experiments. But starting with half this, that is, 12 inches or 6 lbs. initial pressure, there is only about one-eighth the required force for effective braking, and this with the Clayton Brake almost immediately leaks away. In practice a vacuum of 20 inches on the gauge is above the average when running, but even with this initial pressure the resulting brake- block force is only 13,554, or 40 per cent, of what it should be, and 30 seconds after full application it has leaked down to 7,291 lbs., or under one-fourth of the required amount ! The first five columns of Tables I. and II. are applicable to any automatic vacuum brake, but the remainder are rendered necessary by the leaking-off provision of the Clayton brake. With the Clayton brake it is impossible, with a size of appa- ratus practically applicable, to get enough force for really efficient working. To obtain 30,000 lbs. of brake force would require an effective pressure on a piston of the size now used of 26 inches, or 13 lbs. per square inch. This, again, would require an initial vacuum * The full diameter of the piston is 18 inches, or equal to an area of 254-4 square inches. The effective area, however, is that within the rolling rubber packing ring, the diameter of which is only 17I inches, which gives an effective area of 2337 square inches. C lO of about 32 inches, which is, of course, out of the question. As already mentioned, 20 inches initial vacuum is above the average, and this gives less than 6 lbs. per square inch effective pressure. If more power is to be derived from the apparatus, the sizes must be increased in the proportions illustrated by the tables ; but such increase would make the brake much more cumbrous and costly to begin with, and render it slower in going on and coming off, with a conse- quent enormous increase in the expenditure of steam. It may be said, the leverage might be increased. But this means increased stroke, and the evil effects of this have already been pointed out, and will be further plainly seen by diagram No. 10, taken from 20 inches initial vacuum and a stroke of 6 inches. Com- paring this with diagram No. 9, also at 20 inches vacuum, but with only 41^ inches stroke, we find a difference of 2,0001bs. brake-block pressure per carriage, due to the 1 2 inch increase in stroke. The serious reduction of the initial pressure is unavoidable. It must be pointed out, however, that increasing the stroke results not only in a decrease of the power above the piston, by diminishing the capacity of the reservoir, but it also has the effect of delaying the application of the brakes ; for, by increasing the capacity beneath the piston, the volume of air which has to flow in to destroy the vacuum is thereby largely augmented : the principle, therefore, is doubly- defective. The amount of vacuum maintained while running is by no means a fixed quantity. As already shown, the brake is constructed so that no degree of vacuum obtainable would be sufficient ; but so far from even a mean of 20 inches on the gauge being attained, it is a fact that drivers consider them- selves fortunate when they can keep 14 or 15 inches; and there is a delusion abroad that even zuith 10 i?iches on the gauge effective zuork may be done. Now at 14 inches, or 71bs., the resulting brake-block force is only 6,426 lbs., or less than half that derived from 20 inches; while at 10 inches there is practically no power at all, the work of arresting the train being done alto- gether by the steam brake on the engine and tender. The eflEiciency of an automatic vacuum brake, therefore, is vastly lessened by the slightest reduc- tion in the vacuum which is being maintained for its operation. The loss of 2 lbs. initial pressure per square inch means a loss of nearly 6,000 lbs. effective brake-block force per car- riage, and should the initial pressure decrease one-tenth, or from say lO to 9 lbs. even, it signifies a loss of 2,400 Ibs. per carriage, or about one-fifth of the brake force. Various causes may affect the amount of vacuum ; such as the length of the train ; the pressure of steam in the boiler ; and the condition in which the apparatus is kept. It has now be:r come a very difficult matter for drivers running trains fitted with the Clayton brake to maintain the maximum pressure of steam in the boiler, for the difficulty in releasing the brakes compels constant recourse to the large ejector, and cases have been known where the boiler pressure has been reduced from 140 lbs. down to 90 lbs. in the endeavour to release the brakes. More- over, an ejector which will work well at 140 lbs. will probably work very badly at 20 or 30 lbs. less. The above facts thus prove the construction and principle of the Clayton brake to be such that : — I. There is not sufficient brake force for really effective work under the most favourable conditions, and the real amount existing is very much less than it appears to be. At 20 inches initial vacuum, to take a high average, the loss of effective pressure caused by the movement of the piston in performing its stroke is over 40 per cent. ; at |ths of this initial pressure, or 12 inches, there is a loss of 73 per cent., and the 12 remaining 27 per cent., or 31^ lbs. on the square inch, is merely sufficient to bring the blocks fairly against the wheels, and that for a few seconds only. 2. In the effort to maintain a vacuum and to release the brakes the boiler pressure is seriously affected. This not only influences the power of the engine, and the ability of the ejector to maintain a vacuum at all, but it leads to an enormous waste of fuel. The consumption of coal, due to this brake, amounts, at a moderate computation, to over 2 Ibs. a mile. 3. In consequence of the above, drivers often run with the brake shut off, or with such reduced vacuum (for instance 10 inches), as to amount to the same thing as having no brake at all. In practice, only a few inches of vacuum are created before the train is started, and in a couple of minutes the small ejector is supposed to get a sufficient degree of vacuum ; but in the meantime the train has attained a considerable speed, and unless the vacuum exceed 7 or 8 lbs. the brake is comparatively useless. To prevent having difficulty with long trains, drivers have found that even when their steam is high, it is a capital thing to run with only 10 inches of vacuum, " because the brakes are then so much easier to get off!" As already shown, this feeling of relief of course arises from the fact that there is practically no brake at all at 10 inches, since this trifling power is at once dissipated by the simple stroke of the piston. Moreover, the lower the vacuum, the more readily the pressures upon both sides of the piston are equalized, and the brakes thereby released. The time for the application of the brake as shown upon the diagrams is no doubt in excess of what it is in practice, since these diagrams have been taken without any auxiliary means of increasing the rapidity of the brake's action. They 13 show, however, what the principle of the automatic vacuum brake is worth, and how absolutely essential for obtaining quicker action are the inlet valves in the guards' vans, and the leaky piston rods on every carriage. That from ten to twenty seconds should be allowed to elapse, before getting only half the power necessary for effective braking was, of course, out of the question, and led to the desperate remedies referred to. But these supplementary inlets are very objection- able in themselves. The valves in the vans frequently stick open, and thus prevent any vacuum being created at all ; they must be made exceedingly sensitive in their action, so as to operate on the slightest fluctuation of pressure in the train-pipe, or they would be of no use upon long trains where they are most required, and in the same way they must also act upon short trains when least required. It is, of course, impossible to graduate the brake, and trains are often pulled up at the wrong part of the platform by the brake going full on against the will of the driver, and when the speed demanded only a slight application. It is a common thing to see trains fitted with this brake, being dragged into the station with the regulator wide open, and the large ejector blowing at the same tijne to release the brakes ; if the ejector is not carefully handled it will result in the brake being again applied, by jerking open the guards' valves once more. It follows then that this device, to be of service when most wanted, must be so constructed as to be seriously detrimental in ordinary working. Indeed, if it were not for the leak-holes in the pistons, the stoppages and delays would have rendered the brake quite impracticable. It is easy to comprehend how the Clayton brake can be made to give fair results on a short experimental train with everything in first-rate order, and especially when assisted by a powerful steam brake on the engine and tender, the weight of which constitutes a large proportion of the braked weight of the train : it is quite as easy, from a study of the tables and diagrams, to understand how it can, and does give bad results in ordinary working. 14 But it may be asked by some, what are the circumstances when compressed air is the agent employed instead of vacuum ? In the first place, with the air-brake, a large amount of power is carried in a small compass, instead of a small quantity in a very large compass, as is the case with the vacuum brake. Secondly, such power, as in the Westinghouse Brake, is available to be drawn upon many times without replenishing ; while the Midland brake has only one charge, which, when the brake is applied shortly disappears, and can only be replaced after the lapse of more than one minute. Thirdly. In the Westinghouse Brake, the loss of pressure by expansion from the reservoir into the brake cylinder, is nearly constant at all pressures, and so long as there is any pressure at all in the reservoir, a large proportion of it is available in the cylinder. Thus 75 lbs. initial pressure in the reservoir gives an effective pressure of 60 lbs. in the cylinder ; 50 per cent, of the 75 lbs., or 37^ lbs., gives 287 lbs. in the cylinder, or 48 per cent, of the 60 lbs. With the Clayton brake, if the vacuum of 20 inches be reduced 50 per cent., there remains vir- tually no power at all. Fourthly. Owing to the high pressure and abundant power in use, the stroke of the pistons with the Westing- house Brake may be much longer relatively than that of the Clayton brake. This is a very important point. The stroke of the piston in all brakes is equal to the slack of the brake blocks multi- plied by the leverage, and, in addition, the spring upon the gear, which is something considerable. The evil effects of a long stroke with the Clayton brake have been already shown ; owing, however, to the limited pressure obtainable, a high leverage is necessary, and therefore, to confine the stroke as much as possible, the brake blocks must be. kept very close to the wheels. This, of course, necessitates frequent adjustment for wear, and causes in addition much friction when running, by the rubbing of the blocks against the tyres. 15 Now the blocks of the Westinghouse Brake may be moved twice as far as those of the Clayton brake, so that the Westing- house blocks always hang quite free, and the adjustment for wear is only required half as often. When the blocks of the Midland (Clayton) brake are worn so far as to make the brake almost useless, an equal amount worn off the Westinghouse blocks leaves the brakes still capable of acting with full power. There are many other advantages besides the foregoing, which a pressure brake such as the Westinghouse possesses over the vacuum, but as they do not relate so much to the immediate object of this paper, and have been fully treated on in previous pamphlets, no reference need now be made to them in detail. In the annexed diagram the effects of both the Westinghouse and Clayton systems are clearly shown. The vertical lines show the various initial pressures for both brakes, and the horizontal lines the amount of brake force developed at those ^pressures. The average running initial vacuum is taken at 20 inches for the Midland brake, and the diagram for this is constructed from Table I. before referred to. The Westinghouse diagram is made by calculating the cylinder pressures resulting from the various initial pressures when the brake is full on ; the standard pressure being taken at 75 lbs. per square inch, and the stroke of the piston at 6 inches. Now to compare the two diagrams. On the application of the Westinghouse Brake, the pressure is reduced from 75 lbs. to 60 lbs., which is equivalent to 30,000 lbs. of brake force. At 70 per cent, of the 75 lbs., or at 52^' lbs. initial pressure, the brake force is 20,625 lbs. ; at 50 per cent., or 37^/^ lbs. initial pressure, it is 14,375 Ibs. ; and at 30 per Cent., or 22^ lbs., there are 8,125 IbS. of brake force Now, looking at the vacuum line, the apparent power falls, to begin with, from 20 inches to 11^ inches effective vacuum, or from 20,000 to 13,554 Ibs. In other words, this, the greatest average brake force of the Clayton brake, is i6 equivalent to the power exerted by the pressure brake when the initial pressure of the latter has been reduced about 50 per cent., or to 36 lbs. per square inch. At 70 per cent., the Vacuum has only 6,246 IbS. brake force, or less than half that at starting, and is equal to 24 per cent of the Westinghouse, or the force derived from 18 lbs. initial pressure. At 50 per cent., the vacuum brake force has only 1,752 Ibs., or practically nothing. This is about 13 per cent, of what it was at starting, and less than 10 per cent, of the Westinghouse, or than the force derived from 7^ lbs. initial pressure. There is now no further power with the vacuum, while the pressure brake has only been reduced 50 per cent., and the brake force remaining is more than the vacuum began with. Put into figures the diagram reads thus : — WESTINGHOUSE. 1 CLAYTON. Initial Pressure in Auxiliary Reservoirs. Pressure in Brake Cylinders when Brakes are full on. Brake Block Force. Initial Vacuum in Reservoirs. As lbs. pressure Vacuum when Brakes are full on. As lbs. pressure Brake Block Force. lbs. 75 67-5 60 52"5 45 37-5 30 22*5 15 75 lbs. 60 5376 47-5 41 25 35 2875 22-5 1625 10 375 lbs. 30,000 26,880 23,750 20,625 17,500 14,375 11,250 8,125 5,000 1,875 lbs. 10 1 9 ; ^ ; 7 6 5 4 3 2 lbs. 5-8 475 375 275 17 75 nil nil nil nil lbs. 13,554 11,100 8,763 6,426 3,972 1,752 nil nil nil nil )f the Westinghouse and Clayton (Midland) Brakes, at r their standard pressures. i6a 4 — I — \ — I < — m (Co X xespondin^ Initial I — ^^JPressui in lbs. V> S^ m s ^ ^ 1 ^ <^\ «^ 1 Ni >^ ^ ^ •^ '•i ^^ ^ vo N ^' ^ •<* 5^ .*S. >) ..<- Si •*!?< T^ ^ 1 J^ G 6 -f- jTf?itial decnces of ifFdcentaoc of I Slanda rrf 1 'arutiw Diagram showing the comparative eflBciency of the Westinghouse and Clayton (Midland) Brakes, at various degrees of their standard pressures. 17 The initial pressures in both cases are reduced by one-tenth of the standard pressure every time. It will be noticed that, in the case of the Westinghouse brake, the proportion of pressure lost by expansion from the reservoir into the brake cyHnder, practically does not vary, from 75 lbs. down to 30 lbs. initial pressures. Of course the loss, such as it is, is considered in designing the sizes of the parts, but however great it might be, the initial pressure which can be carried is practically unlimited, and therefore the loss is of no conse- quence. In the case of a vacuum, on the contrary, the pressure avail- able is so small, to begin with, that the slightest loss is of immense importance ; and, as has been shown, when the pressure has been obtained, it has a marvellous power of being easily reduced. Upon a previous page mention has been made of a very important defect in the Clayton brake, viz., that having only one charge of power, the brake is not available for several applications ; in fact, it often becomes necessary to obtain a fresh supply of power while the train is still running. During the process of re-charging, or re-creating the vacuum, the brakes must, of course, all be " off," and without any available power ; the length of time, therefore, necessary to procure anything like an effective brake force is obviously of the greatest moment, especially when approaching junctions and termini, and par- ticularly in foggy weather, and upon down gradients. Experi- ments have therefore been made, with the view of ascertaining the interval which must elapse, before the train can be again provided with a continuous brake, after the first supply of power has been dispersed, and the following indicator diagram showing the results will no doubt be studied with interest. The experiment was made upon one vehicle only, and to make the circumstances as favourable as possible, a vacuum equal to 12 lbs. pressure was maintained in the train-pipe from the beginning, while the time taken to produce various degrees of vacuum adove the piston was recorded. Under these circum- stances the flow of air through the leak-hole was, of course, more rapid than could possibly take place in practice, since the time necessary to exhaust all the air from the pipe, and from beneath all the pistons of a long train, was disregarded. Diagram showing the time required to produce various degrees of vacuum above the piston in a Clayton cylinder^ but with 24 inches, or 12 lbs., mainfaifted in the trainpipe. In the following table the results are shown in figures Number of lbs. Time in Seconds. 2 6 3 10 4 15 5 22 6 28 7 36 8 45 9 56 10 66 " 82 19 In practice these times would be certainly increased, with any size of ejector in use, but the figures as given are surely striking enough. Imagine, however, a train still running, perhaps at thirty miles an hour, and even the very inadequate power which, as has been shown, results from a vacuum of 20 inches, or 10 lbs. pressure, being unobtainable for a minute and a half or two minutes ! The great danger of this feature, however, lies in the fact that when the brakes have leaked off once, drivers are often beguiled into thinking they have created a further supply of power upon which they can rely for a second application, when, in reality, they have done nothing of the sort. Upon opening the large ejector a high vacuum may in a few seconds appear upon the gauge which is close by ; but this is no indication of the amount of pressure on the top side of the pistons and in the reservoirs throughout the train. Now, the brake may often be required for a second or third application, before there has been time to re-create a vacuum, even when all is in perfect order. But if things are not in good order ; suppose some couplings are leaking ; that even one of the brake pistons from any cause has failed to seat properly, either through the twisting of the rolling rubber piston packing, the deterioration of the rubber seat, or the stopping up of the leak-hole (as mentioned in Colonel Rich's report) ; then, it would be impossible to obtain sufficient vacuum for effective work at all, because air would be drawn in round the unpacked piston rods, or through the leaky couplings ; yet at the same time a vacuum of from 20 to 24 inches might be registered upon the gauge ! Is it any wonder, then, that drivers are entrapped into running past signals and platforms and into buffer-stops P In the case at Portskewet Pier, the brake failed, as Colonel Rich shows, in the most commonplace way, and this v/as at an ordinary and expected stopping place. But, imagine a heavy train running down hill in a thick fog up to a crowded junction, 20 or terminus, with numbers of fouling places and signals, for the last two or three miles (there are hundreds of such places throughout the country), and that the driver, as is most likely, has been called upon to use his brake ; that, before coming to a stand the road is cleared for a short distance, and the train runs on, still at considerable speed ; and that then, shortly after, in obedience to another signal, perhaps a fog signal, there is urgent need to stop, but that, from either of the causes just mentioned, which are quite independent of the driver, there is no vacuum ready formed ! Colonel Rich, in the report alluded to, describes a casual experience of this kind when running up to Taunton Station, and the consequences which might ensue are only too clear ; but it should be understood that the risks mentioned are now run daily and nightly ; that, so far from its being a rare occurrence, stations and signals are frequently over- run, many cases having occurred at Bedford, and Kentish Town, alone, on the Midland Railway. There is no doubt, too, that the collisions with the buffer-stops at Bradford last June, and on September 22nd at Liverpool, were due to the same causes, Vide , , . , . 1 1 Appendix, and that the drivers were utterly powerless to prevent them. If it were not for the steam brakes upon the engine and tender (which, be it remembered, form no part of the continuous brake system), many more serious accidents must have resulted upon the Great Western and Midland Railways, simply from the inefficient and treacherous character of the vacuum brake. If the leak-holes in the pistons were larger, no doubt the vacuum would be re-created more quickly, but at the same time the brakes would leak off so much the sooner ; and it would seem that even the Midland and the Great Western Railways would not care to incur the risk of using a brake which was intended to remain on less than a minute and a half. In face of the delay which has occurred in the adoption of a brake, owing, it was said, to the difficulty in deciding upon which was the best^ the comments made herein may read to the 21 uninitiated almost like a fable, and it may well seem incredible that any Board of Directors should allow money to be wasted in such an exceedingly useless way. We are, however, fully prepared to prove the truth of our statements ; and as some confirmation of them, we insert here the principal portion of the conclusion of Colonel Rich's report upon the Portskewet accident. The heavy type and italics are our own. " The collision was caused by the vacuum brake " failing to act when it was required In the " present case the engine-driver appears to have been running " at the ordinary rate of speed, so that he might have pulled " up his train at the pier platform, by calling for the ordinary " guard's hand breaks and by using his engine brake. He " appears to have touched the lever of the vacuum " brake three times slightly, so as to control the speed of " his train, as he descended the incline towards the pier ; and, " at the last moment, when he found that he was running close *' up to the empty coaches, and tried to stop his train by means " of the vacuum brake, which he ought to have been " able to do, this brake failed to act. " I believe that the brake failed to act in consequence of " there being a very small amount of vacuum in the pipe and " cylinders, possibly none, as the train approached the pier, " after the driver had applied it three times during the short " journey from the junction. " I think the efiiciency of this brake has been " materially interfered with by the hole in the pis- ''ton rod, which allows it to leak off in a short " time. " I experimented on the carriages of the 6.40 P.M. train, which " were standing at the Portskewet Junction when I made my " investigation, and I found that the brake leaked off the van, ** which was next to the engine, in about thirty seconds. It " leaked off one of the coaches near the tail of the train in " about two minutes ; and the brake on one of the other 22 •* coaches near the centre of the train held for more than " five minutes, probably owing to the hole being *' stopped up. •'The effect of these brakes is dependent on the extent of the " vacuum. " While running into Taunton station on the engine of the " express train to Plymouth, on the same day after my inquiry, " there seemed to be a very considerable leakage in the vacuum *' brake. The ejector did not rise the gauge beyond 20 inches, " and this leaked off to about 7 to 9 inches before the train left " Bristol. After leaving, the pump rose the gauge very slowly " to about 22 to 23 inches while the train was running, but the *' zvhole of the brake pozver appeared to be exhausted before the " train was half stopped when running into Taunton station, so " that at that momeittous time there was actually no continuous " brake available until the vacuum was recreated by the applica- " tio7i of the ejector, after which the train was stopped at the " platform. I doubt zuhether this was considered by the engine- ** driver as a failure of the brake, and zvould be reported as such ; " to my mind it was a very important failure. " I have, &c., " F. H. Rich, " The Secretary, " Colonel R.E. " {Railway Department,) Board of Traded The above strongly supports the position which has been taken up. It is instructive, too, to learn that one brake leaked off in thirty seconds, while another remained on five minutes, "probably owing to the leak-hole being stopped up !" In other words, this contrivance only acts with any semblance to a brake, when it fails ! Is not then the conclusion arrived at in a previous pamphlet fully justified— viz., that, ''real efficiency, and therefore safety, has been sacrificed to obtain a delusive appearance of simplicity"? 21 It may be asked, why use such a questionable contrivance as the leak-hole ? The simple answer is, to avoid the delays to traffic, which would otherwise render the use of such a brake impracticable. On behalf of those who have not studied the question, it may be as well once more to explain this matter. In the endeavour to provide a brake, other than the Westing- house, which would comply with the very necessary conditions laid down by the Board of Trade, the Great Western and the Midland Railway Companies purchased for small sums the right to make and use an untried apparatus on the automatic vacuum principle. All automatic brakes are applied by reducing the pressure in the train pipe, and thereby allowing the stored- up power in the reservoirs to be exerted upon the brake pistons. It follows, then, with such brakes that, whenever the couplings are disconnected, whether for shunting or other purposes, the brakes must be applied, unless there is some means of confin- ing the pressure in the train-pipe. With the brake in use on the above railways there is no such provision, and all the brakes are consequently applied at most unseasonable times, that is, when performing the ordinary operations of traffic. The obvious solution was the use of cocks at the ends of each vehicle, such as are employed in the Westinghouse Brake ; but, pipes of less than two inches internal diameter cannot be used with vacuum brakes as at present designed, and it is not practicable to employ cocks for closing pipes of such a size. The Westing- house pipes, being only one inch in diameter, or one-fourth the size of the vacuum, are, of course, not open to the same objec- tion. To release the vacuum brakes then, when separated from the engine, two courses were open — viz., either to attach a valve upon each carriage, which would require to be opened by hand, always with the loss of several minutes, or, by making a hole in the piston, enable the pressures on both sides of it to be equalized, and thus render it impossible for the brakes to remain on longer than a certain time, depending upon the size of the hole. The former plan was soon found to be impracticable for 24 ordinary traffic, and the latter system was adopted. It was felt, however, that the traffic could not be facilitated, and that there would be no gain in forsaking the alternative arrangement of a valve, unless the brakes released themselves very soon : one minute and a half was therefore chosen as the regulation time during which it was desirable the brake should remain applied; and even this brief period depends, as already shown, upon the amount of vacuum which is carried. There was a further important reason which influenced the adoption of the hole through the piston, and this was the diffi- culty experienced in releasing the brakes at all by the large ejector, upon trains of more than ten carriages. This was partly due to the friction in the pipes. Moreover, as regards the Great Western Railway Company, the vacuum is maintained by a pump which is often able to attain a higher degree of vacuum for the application of the brakes, than the ejector can overcome for their release. Further, as the pump is driven from the cross- head of the locomotive, it varies in speed as does the engine, and sometimes stops altogether. The higher the speed, the greater the degree of vacuum which can be obtained ; and when the speed reduced, the fluctuations in the train-pipe, and on one side of the valve, were considerable, and the brakes naturally went on. In fact, there were undoubtedly very strong grounds for resorting to this hole for equalizing the pressures, and releasing the brakes ; and though, in comparison with other arrangements, such a method is of course not to be commended, it is certainly of the greatest importance to the Midland and Great Western S5^stems, since it is clear that without it those Companies have found their brakes to be quite impracticable. Even now, as has been stated, there is often very great diffi- culty in getting the brakes ofl" on long trains, if anything but a very low and consequently useless amount of vacuum is main- tained. Indeed, the use of any automatic vacuum brake, as at present constructed, is quite out of the question upon trains of twenty carriages. Thus, we see that the Great Western and Midland Com- 25 panics were reduced to the necessity either of destroying the brake power almost as soon as brought into action, or, of abandoning the appliance which had been so strongly recom- mended by their officers. They chose the former : in the public interest, and in view of the fact that there was another system available, constructed upon a principle which enabled it to fulfil all necessary conditions, without incurring risks or delays, a more unwise course could not have been pursued. The Westinghouse Brake Company has at all times sought to arrive at the truth, and has always encouraged the fullest examination of its brake apparatus by friends or opponents. It has further gone to considerable expense in erecting a great variety of compressed air and vacuum apparatus, in addition to that of the Clayton Brake referred to in these pages, and has repeatedly invited all those interested in the question to come to the Company's works, and, by personally experimenting, satisfy themselves of the correctness of the view that Auto- matic Vacuum Brakes can never be made to compete as safety appliances with Compressed Air Brakes. Those who have responded to this invitation have been greatly impressed by what they have seen. The Westinghouse Brake Company, Limited. Canal Road, York Road, Kin^s Cross, London. APPENDIX. Since the foregoing was printed, Major Marindln's report on the collision with the bufifer-stops at the Central Station, Liverpool, has been issued. This case has already been referred to on page 20, as illustrating one very great defect of the Clayton (Midland) and Great Western brakes, viz.: that after they have been applied and have released themselves, it is impossible to get a further supply of power, or to re-create a vacuum in the reservoirs throughout the train, so soon as the necessities of the case demand, and that this is a most dangerous feature in those systems. The remarks of Major Marindin on the behaviour of the Midland brake at Liverpool, fully confirm what we have said, and also support the views of Colonel Rich as to the defects of similar apparatus on the Great Western Railway. Appended is an extract from the conclusion of Major Marindin's report : the heavy type and italics are our own. After censuring the driver for not running into a terminal station at such a speed that he might have stopped by means of hand-brakes alone, the Inspector goes on to say, — " It would, however, appear from the evidence that "the breaks upon this train did not act as they "should have done when they were last applied, " for, if they had, the train break, which was undoubtedly " applied when leaving the tunnel mouth, 3 1 1 yards from the " buffer-stops, or very soon after, ought certainly to have so " reduced the speed that the driver might without difficulty " have stopped his train at the proper place, by the application " of the steam break when he had still 140 yards to run. 28 " It is impossible to say, with certainty, whether this was " due to any fault in the hanging parts of the break, such as " the blocks being too far off the wheels, or to the driver not ** having taken steps to maintain the necessary power ; but, as "the breaks seem to have acted well throughout the journey, " and were found to be in good order after the collision, I believe " that the failure to act properly was due to the latter cause. *' The statement of the driver that his train break and steam ** break were both full on from a point 30 or 40 yards inside "the distant-signal to a point 100 yards outside the home-signal, "that is, for a distance of 560 yards, is clearly incorrect, for, if "this had been the case, the train must, if the breaks were " worth anything, have been stopped altogether in the tunnel ; " but, taking the statements of the fireman and guards as being "more accurate, it is clear that the train break was on to some " extent for a considerable distance and time before the driver "released it upon sighting the home-signal. The rear guard "says that it was released when near the home-signal, but did " not come fully off, and that, when applied again, it did ^'not seem to act properly; while the front guard " says that it came fully off the front break-van, and " that he does not think the blocks came on again " upon the front break-van at all. " It is probable, therefore, that the break was applied slightly " only after passing the distant-signal, and remained slightly on " until the home-signal was sighted, the power gradually "diminishing on account of the leak-hole in the " piston-head ; that, when the driver released the break near " the home-signal he did not make sufficient use of his large " ejector, and consequently did not take the break fully off, " and did not create a sufficient vacuum to render " the break effective when he resorted to it after " leaving the tunnel. " It is true that the driver states that he saw that he had ** blown the vacuum to 15 inches on the gauge, but he was then " in the dark and may easily have made a mistake, while it is 29 " rather remarkable that the number of inches which he has " stated, viz., 15, is the minimum number at which he is allowed " by the rules to run. "/ t/imk that the unsatisfactory matiner in which the train " break behaved upon this occasion strongly supports the conclusion " which was arrived at by Colonel Rich, when reporting upon " the somewhat similar accident which occurred on the 2^th April, " 1882, at Portskewet on the Great Western Railway, viz., that "the efficiency of this class of break is materially "interfered with by the leakage hole in the piston- " head. ******* " I have, &c., '* F. A. Marindin, " The Secretary, ** Major. " {Railway Department^ Board of Trade!' As has already been explained, the fact that it takes so long to obtain a further supply of power with the Clayton brake arises from the defective priiiciple of the apparatus, and is entirely outside the control of the driver. Though animated with the best intentions, the driver could not procure 20 inches of vacuum throughout the train under one minute and a half. LE I. ,ges, fitted with the Clayton (Midland) Brake. ,'om the 10th Carriage. To match Diagram No. 3. [ Vide page 6. IS seconds after full appl ication. 30 seconds after full appl ication. ve pres- kr square if brake Ston. Resulting brake block force. Brake block force wanting for effective work. Effective pres- sure per square inch of brake piston. Resulting brake block force. Brake block force wanting for effective work. 1 lbs. lbs. lbs. lbs. lbs. •75 18,111 11,889 5-5 12,853 17,147 •25 14,606 15,394 4-25 9,932 20,068 •0 11,685 18,315 312 7,291 22,709 ■12 9,628 20,372 2-5 5,842 24,158 •8 6,543 23,457 1-6 3,739 26,261 ■0 4,674 25,326 ■75 1,752 28,248 •0 2,337 27,663 ! -2 467 29,533 3 701 29,299 nil nil nil L E II. taken from the 8th Carriage. To match Diagram m. 7. bs. lbs. lbs. lbs. lbs. lbs. r-8 18,228 11,772 58 13,554 16,446 55 15,190 14,810 4-75 11,100 18,900 525 12,269 17,731 35 8,179 21,821 vo 9,348 20,652 2-6 6,076 23,924 ?'0 7,011 22,989 1-8 1 4,206 25,794 ^■4 5,608 24,392 1^0 2,337 27,663 1-0 2,337 27,663 •25 584 29,416 2 467 29,553 nil nil nil TABLE I. Experiments with a Train of Twenty Carriages, fitted with the Clayton (Midland) Brake, stroke of Piston, 4)j inohea. Reaidts taken from the 10th Carriage. To match Diagram No. 3. [Videpagt 6. i Initial pressure in lbs. per square inch beforeapplcia- Time required to get brake .„o„. At ins ant of full applic ation. ■5 seconds after full application. 3oseco„ ds after full appl cation. Effective pres- Resultingbrake block force. Brake block force wanting for effective work. Effective pres- Tnch'^lf brake" Resultingbrake block force. Brake block fofeffeS've^ work. Effective pres- sure per square inch of brake ^'£-1^'^' Brake block force wanting for effective work. Ibs. Seconds. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. 12 12 8-3 19.396 ,,,604 7-75 i8,iu 11,889 5-5 12,853 17,147 II .2 70 iS.SSQ 13.641 6-25 14,606 15.394 4-25 9.932 20,068 10 12 • 5-8 13,554 16,446 5 11,685 18,315 312 7,291 22,709 9 9 4-75 11,100 18,900 4-12 9,62s 20,372 i 2.a 5,842 24158 8 9 3-75 8,763 21,237 2-8 6,543 23.457 1 '■' 3.739 26,261 7 9 2-75 6,426 23.574 20 4.674 25,326 1 .75 1.752 28,248 6 9 1-7 3.972 26,02s 10 2,337 27,663 ■2 467 29.533 j 5 9 •75 1,752 28,248 3 701 29,299 nil 1! nil nil TABLE I L Fifteen Carriages. Stroke, 4i inches. Results taken from the 8th Carriage. To match Dia^-am No. lbs. Seconds. lbs. lbs. lbs. lbs lbs. lbs. lbs. lbs. lbs. 12 lO 8-75 20,448 9.552 7-8 18,228 11,772 5-8 13.554 16,445 ■> lO 7-5 17.527 12,473 6-5 15.190 14,810 4-75 ,.,.00 18,900 10 10 625 14,606 15,394 5-25 12,269 17,731 35 8,179 21,821 9 9 50 10,685 18,315 40 9.34S 20,652 2-6 6,076 23.924 8 8 3-75 8,763 21,237 30 7,011 22,989 18 4,206 25.794 7 8 2-75 6,426 23.574 2-4 5,608 24,392 10 2,337 27,663 6 6 1-8 4,206 25.794 10 2,337 27,663 ■25 584 29,416 5 6 •5 1,168 29,832 2 467 29,553 nil nil nil Brake. cuum on a train of 20 carriages ches. N° Mirujtes . ZMtrmtes Experiments with The Clayton (Midland) Brake. Dui'iranis sho^wins the bi-alve hlork pressure exej'ted at various degrees rf vacuum on a train of 20 catT-ia^es. Uiaanuihs f'r-oni J>'' J't/url^ . -Slrckr ol' J'hston 4'i uichcs. Secende Uiac/ratn.s from 4'P} Vfki'cle N°2. N' D ^ Brake N?3 -z::^ — =^ — — 1 — 1 — Sb rji ^- — — — — — — — en ?f> i I r/c; 7/r'' /^^ Ifl t* l€ IM^ v^n H< .*£ fjt _ . . ^ __ . __ \ — - [ 15 10 l___ r -^.^ =_, zrr ■ — __ — — 1 T -L --- ^ T ± v 1 1 T T" ■^ I tr L ^ -jt- t L_L 20 40 50 Mirvuutes N°4-. = = i — 1 P^ — 1 — Sh 1 — 30 Ifi ___ ?/ tU r,T/ y,rf //' fk ■J: . _ _ . _ . ^. _ _ . . _ -tr- io 1 5 r— -^ — — — — — — — X I 1 1 T rr h- ~r 1 T T i T" 1 1 T 1 -^ 1 I Y -r- 1 1 1 w 30 40 50 ^ ^ ^ ZMiruiies THO* KELL ot SON . LITH 40, KING S-* CO'^NT GARDEN Experiments with The Clayton ; M i d j- a r.' d j Brake JJuufrtiiiis irxtia 10*'' J'ehiclf; . N?3 JJutq/ciniN I'toiii U*^' Vcln'clc N?4-. \ N D ) Brake w 2 inches . 30 40 N°5 — -^ 3b . ' 30 ts — rt fir ii(( , , in 7 1 \h /77 tl fj< (t ( h ic /'f' -" 1 1 — ' ^~ 25 ' — ^ ^ fe f-r it' hf Ir Jj:± t^ '/' 717 < •^rt >} 0/7 1 1C' = =- — « =^ fer- 1 ' 1 — ^- — — 1 — 5 = =^ "— == ^ ^ :^ ^ — A - ' — ' — -— ^ — — ■ ^ T 1 -j- T 1 T 1 1 1 1 T T- 1 M- I 1 1 X T T T 1 1 , 20 40 50 ^ ZMirvuutes chicle N9 8. -j — — — — — k- '65 — >i ^0 C s:: 1^ 25 stf ^S ^ Q> . '^ 'Y^, ^ t ?/^ va tff \t' > IV ' / r/ ^/// ' f' fSf ■)f(, W 75 W 5 \z. 3 YEW s^ — — . — 1 H ^ J5 f^ r— ^ fsS ^ jy ^ 1^ M ^ ..^ t^ - ^ t>SM ^' '^' ^ - - - -1 b= „^j. .^_ ' — ' »— , _ • \—r- 1 i Y 1 1 I 1 1 T T T "J" 1 T T 1 X T 1 T 1 1 T ■ _ _ 2 3 4 rao^ KEJ L * 5 SON ra 4 O.KI NG S^ C Muiujtes T GARDEN ^ Experiments with The Clayton (Midland) Brake 15 (xnricuf&s . Buicfrajris from 8*^^ Vehic^ii . N? 7. 15 Cafrraqc.s . Biaqrains from 15^^! VcJdcLc N? 8. NaK E . N° 9 w rti 35 3V nr 30 40 50 25 p W ^ 15 ^ Jo w ZMifuztes 1^ Ccurrtax^e 20^ , — — N o 10 1 — — — ~ — 1 — ! . Sy ^ 25 '^ \~-'~~ ^ 9/J ^ ^ ■ « \ ^2 ^s ■■ § c> ' 1 I i \ Lj I 1 1 '] 1 1 L 1 L I 1 1 1 Ll_ w 3 4i 5 ZMiruates Experime nts with The Clayton (Midl and) Brake GojiLiJar-ative diagrams at 20 and 10 inclies vacuum. W Carriaqes . 4 k Str^okf Seconds o LomparLs'on at G inches strohr. . /*f Carriaqe N?IO. ^ m w m .H -Ik. 4 *-4h /*^*^**r %-^ i * \ -fUft*^ %^^ ^^ ^m % ■St.' h t ^^ ^W'