PLATE 87-No. 3-E CONTROL VALVE, P-C PASSENGER Preliminary Release Position (Diagrammatic View) CAR BRAKE EQUIPMENT # ATMOSPHERIC PRESSURE CHAMBER SERVICE CYLINDER EMERGENCY RESERVOIR APPLICATION CHAMBER ISOLATED PORTS AND CHAMBERS ERRATA-Chamber D being isolated from other pressures in this position, the pressure therein should have been designated by Brown instead of Orange (or Atmospheric), but unfortunately the error was not discovered until the printing was completed. PUBLISHED MONTHLY BY THE BROTHERHOOD OF LOCOMOTIVE FIREMEN AND ENGINEMEN COPYRIGHT, 1914, BY JOHN F. McNAMEE Entered as Second-Class Matter January 21, 1914, at the Post Office at Columbus, Ohio, VOL. 57 No. 3 COLUMBUS, OHIO, SEPTEMBER 1914 Plate 87-No. 3-E Control Valve, After a service application has been P-C Passenger Car Brake Equipment (Diagrammatic View)-Preliminary Release Position. made, no matter in which of the two lapped positions-noted above-the Control Valve may stand, a recharge of brake-pipe pressure will cause its equalPlate 87 of the Westinghouse Air izing piston and the release piston with Brake Series of the Locomotive Firemen their attached valves to return to the and Enginemen's Magazine Educational release position-or to the graduated reCharts represents the No. 3-E CONTROL lease position; the positions are the same, VALVE of the P-C Passenger Car Brake the only difference being that if the Equipment in a diagrammatical section brake-pipe pressure increase-rechargeview, with the operating parts in the is not interrupted it may be called the PRELIMINARY RELEASE POSITION. This "release position"; but if the rise of re. position-chart may appropriately follow in direct sequence the charts previously published, of either the Service Lap or the Over Reduction Lap positions. In these diagrammatic charts of the Control Valve, all operative parts, air chambers and ports that do not come into play in this position, are omitted, to simplify the charts and make the different phases of the Control Valve's operation the very easiest to understand. charging pressure is stopped, by placing the engineer's brake valve in the lapped position after only a portion of the brakecylinder pressure has been exhausted, the same position of the Control Valve parts is termed "graduated-release position," but it will be followed at once by the Control Valve automatically assuming the position of "graduated-release-lap." After a service application the recharging of the brake pipe forces the [Errata.-Chamber D being isolated from parts of the Control Valve to release other pressures in this position, the pressure position in a general movement covering therein should have been designated by Brown on the accompanying chart, Plate 87, instead of no more than two or three seconds; yet, Orange (or Atmospheric), but unfortunately within this short space of time, there the error was not discovered until the printing is a series of limited movements in the was completed.-Editor.] direction of their release positions by the equalizing, application and release portions, in which the termination of a certain action in one portion is necessary to permit the start or continuance of another portion, etc., thus forming a short chain of events that must be viewed separately in order to gain a proper understanding of the release action as a whole; this is provided by considering that there are three stages in the releasing operation, and explaining them with reference to three corresponding charts that represent each stage as a separate "position" of the Control Valve parts; the first (the subject of the present plate) is called Preliminary Release Position; the second, Secondary Release Position; and the final one, Graduated Release and Release Position. Referring to the present chart, Preliminary Release Position, brake-pipe air in chambers A and B has the same pressure against the equalizing and release pistons, and there were equal pressure resistances on the opposite sides of the piston heads, but the equalizing piston is freer to move (on account of less slidevalve frictional resistance) than the release valve, and at the point at which this position was taken the brake-pipepressure increase while not yet having become great enough to move the release piston, has forced the equalizing piston and its attached valves downward to the position shown; at this stage-a little short of completing its full stroke to release position-there is a momentary pause in the movement of the equalizing piston through having met with an added resistance, the smaller (lower) end having abutted against the equalizing stop and closed the equalizing port that connected chamber F with chamber D, there is the resistance of the equalizing-stop spring and the air pressure in chamber F, which is in direct supply from the pressure chamber. Another connection occurring at this stage for a brief moment only, is that chamber E behind the release piston, is connected through ports in the equalizing slide-valve and graduating valve with the reduction-limiting chamber exhaust-port; it is a necessary feature, and provides for the next stage of the releasing operations -the initial movement of the release piston-which will be represented in the chart to follow, this exhaust-port connection insuring a momentary but material drop of the air pressure in chamber E below that of the brake pipe in chamber B on the opposite side of the release piston; to afford time for this to take place is the reason for the tempo rary pause of the equalizing piston as already explained. Meanwhile, the reduction-limiting chamber begins emptying itself of pressure of air which, as already explained, has had nothing directly to do with the application of the brake-the port from the reduction-limiting chamber now being connected by way of a cavity in the face of the equalizing slide-valve with the reduction-limiting-chamber exhaust port leading to the atmosphere; and this exhaust-port connection is maintained through the subsequent stages in the release movement of the Control Valve. Release of brake-cylinder pressure has not yet commenced, as there has not been, so far, any discharge of pressure from the application chamber and chamber C on the left of the application piston-this piston remaining therefore in the lap position, with the ports in both its application and release valves closed; this inaction is brief, only lasting until the continuing increase of brake-pipe pressure has forced the release piston and its attached valves to their full release position, which will be described with reference to the next chart to follow-"secondary release position." "Braking Power"-Its Interpretation and Its Application. With Particular Reference to Passenger Service.* The brake which can transform the fluid pressure of compressed air into a very great mechanical force needs a foundation gear adequate for the development of this force, and, if it is not provided, distortions, shifting of wheel weights, unequal division of the force to the wheels, binding of the wheels in the pedestals, in fact, every conceivable, uncondition in desirable braking may occur to the loss and inconvenience of the road and to the retardation in development of one of the principal things roading possible, namely, the air brake. that has made the present scope of railOf course, most of the ill effects of an improper understanding of the braking ratio problem and of inadequate and damaging designs of foundation brake gear are not apparent in themselves; that is to say, the foundation brake gear is a dormant appendage until the air actuated mechanism per se causes it to Abstract from paper by Mr. Walter V. Turner, Chief Engineer, Westinghouse Air Brake Company, read before The Railway Club of Pittsburgh, at its meeting of April 24, 1914. (1) greater loss than anticipated in co-efficient of the brake shoe, due to the higher forces developed, (2) the greater mass of locomotive which was unbraked, come into action, and since whatever I can well remember pondering over the damage or ill effects result, prima facie, causes for several days and among the must have been caused by the air valve five causes which I finally concluded itself inasmuch as everything was lovely were the reason of this, I found the one until it was called upon to perform. of improper and inefficient design of One might as well blame a train for foundation brake gear-the other four being wrecked by a broken rail, for, being obviously, the broken rail would not have mattered if the train had not come along; or blame the blowing up of a boiler on the steam that caused it, since, obviously, the boiler could not have blown up had there been no steam (3) the larger brake cylinder volpresent, but, in this case, most men of ume without proportional provision for sense blame it either upon improper getting the air into the brake cylinder design or maintenance of the boiler, and quickly, I have hope that some day the same (4) increased length of time in line of reasoning will be applied to the which to get the brakes started throughtwo interdependent and intimately re- out the train, due to longer cars, which lated parts of the air brake, namely, the means greater brake pipe volume to be air actuated devices and the foundation exhausted without adequate provision brake gear through which is trans- being made in increased number or formed the air pressure into a me- efficiency of quick action venting devices chanical force and then transmitted for the purpose. through the shoe to the wheel. All of these five causes were written Suppose, for example, one should down in my note book at the time and design and build a locomotive capable of were copied therefrom today, and I transmitting 40,000 pounds to the know you will pardon the strong sense drivers and then provide connecting of gratification which I feel in the rods capable of properly and effectively knowledge we now have that each one transmitting but 30,000 pounds. What of these was thoroughly investigated in would be the result on the one hand, our recent experiments in brake testing and what our opinion of the designer at Atlantic City and every one abunon the other? dantly confirmed. In fact, a modificaI had gone through several so-called tion of any one of these factors in any air brake tests and had studied con- considerable degree evidenced itself by siderable literature on the subject be- such a wide margin as to be indispufore the commencement of the air brake table. It is because of this, that what tests at Toledo in 1909, and I believe is to follow speaks forth with such asyou will pardon me for saying that I surance, and I have no hesitation in had made something of an analysis of the braking situation and potential, the working out concretely of which has resulted in some very desirable and profitable improvements. But at Toledo and In a discussion of the subject of subsequently in the installation of air braking "power" we are hampered at brake mechanisms capable of develop- the outset with the same difficulty that ing great forces, it was apparent that has been the case, and still is, with the foundation brake gear was very in- many problems in air brake engineering; efficient in transmitting the air pressure that is, the absence of a hitching-post to the shoe on the one hand; and that or standard criterion and by the gendue to distortions, binding of wheels, eral vagueness and ambiguity of our forming of toggle joints, and turning the engineering terms. This may be due to truck frame into a suspension beam for the fact that up to a few years ago, the the wheels, very unequal braking force air brake business was simply a busiproducing surges and wheel sliding, ness and not an engineering or scientific could occur, on the other. development. It was largely a question saying with a period at the end of the statement; that any violation of the principles laid down will result in inefficiency and loss. At these tests, we had every reason, of rule of thumb, or cut and try, and based upon the state of the art at that such methods are not conducive to time, to believe that with the air brake standards. In the past few years, howmechanism recently designed a stop ever, the development has been very could be made, with the braking ratio largely along strictly engineering or to be employed, in 1200 feet, but some- scientific lines, and many of our probwhat to our surprise, it required some- lems have been reduced to an engineerthing like 250 feet more than this, and ing or scientific basis, but still there are some with which it is not the case, and this "braking power" question is one of them. convincing them as to the utility and degree of earning power inherent in a brake, but the layman to whom, if we are to convince and persuade, we must employ terms which naturally he understands, from the fact that they are not arbitrary. Definitions of Braking Power. When one attempts to consider this question, he is confronted at the outset by the realization that "per cent brak- That is, inasmuch as "braking power" ing power" by itself is vague, indefinite, and retarding force have no fixed relaand ambiguous, for unless the context tion to each other, when speaking of clearly brings out the intended meaning, dissipating the energy in a moving train, "per cent braking power" may mean the term "braking power" is ambiguous, the ratio of the shoe pressure to the since the actual ratio of shoe pressure weight of the car, and this either for to the weight of the car per se gives but service or emergency, or both, or it little information as to the actual length may be intended to mean the ratio of of stop, so it would seem that the term the retarding force to the weight of the which should be employed in such cases car, and this again can be for either should indicate the retarding force, by service or emergency, or both. Still this meaning the stopping force actually again, it may mean the former of the realized and not the nominal shoe prespreceding less certain assumed losses of sure of the installation. In fact, such brake rigging, etc. Again, "per cent a term is now used in brake test analybraking power" and "braking power" sis, for the factor of retardation is the are often used synonymously, although ratio between the average actual stopthe latter, strictly speaking, applies only ping force realized and the weight of to shoe pressure, that is, total cylinder the car. pressure times the leverage ratio, which does not necessarily have any fixed relation to the weight of the car, while "per cent braking power" does. Thus it will be seen that in using this expression, one must be careful to state the extent in which it is to be taken by surrounding it with a context sufficiently explanatory to clearly define and limit the speaker's meaning. Braking Ratio and Factor of Retardation. The confusion arising from assuming braking ratio and factor of retardation to mean the same thing, makes it desirable that the terms should be clearly defined, and then it will be seen that the former is better adapted for use when considering brake installations, and the latter, as the criterion of brake Braking Power and Braking Ratio. performance. This will be all the more apparent when it is remembered that It would seem when considering a brake installation that the term "brak- be assured for any given car, even uniformity of stopping distances cannot ing power" or braking ratio, might though the levers, cylinder, etc., are of properly be employed. Preferably brak- the generally accepted proportions, by ing ratio, because "braking power" is a arbitrarily prescribing any braking misnomer, since power is the rate of ratio, unless three other factors can be doing work which is not even a factor in the case we are now considering, and since even when applied to the stopping of a train, no fixed relation exists between the "braking power" and the length of stop. If employed when considering brake performance, it can only be in an arbitrary sense, which is inexcusable if a precise and fundamental term can be employed. known and insured, namely, time to get the required cylinder pressure, the efficiency of the brake rigging, and the coefficient of friction of the brake shoe. With these three things known, the percentage of so-called "braking power," but more properly braking ratio, which must be used to produce a given stop from a given speed, can be determined. In general practice, however, it is practically impossible to know these factors when contemplating a brake installation, therefore, nothing more than "Braking power" is nothing but air brake parlance, for it has no scientific basis and is not a convertible term, and, except the user consciously or uncon- an arbitrary percentage can be desciously translates the expression, it has no practical value. In the writer's judgment, it is not a sufficient justification for its use to say that its various usages are understood by air brake engineers, for we are not concerned about termined upon. This, then, is as far as one can go when considering what percentage of "braking power" shall be employed for general service, or as we may say, arbitrarily determined upon in order to have a working basis. |