Brake Tests

202 Diagrams of Typical Stops. 415. A considerable part of the data taken during tests was obtained by autographic recording devices, and can be combined on a single diagram to afford a convenient means of analyzing the various factors, and the effects which they produce with respect to the general action of the train during the stop. Diagrams of this description for typical test runs are shown in Figs. 117 to 137, in which will be found curves for the speed of the train, the building up of brake cylinder pressure and braking power corresponding thereto, the deceleration in miles per hour per second, and the relative slack movement between cars at various points in the train as observed, all of which are plotted on a distance base with the corresponding time scale for comparison. 416. The deceleration curves are shown only on a sufficient number of representative diagrams to establish clearly the character of these curves. The slack action records are given wherever available. n some cases, no slack action device was used, and in other cases the record is imperfect. 417. These curves show graphically the effect of different rates of retardation at different points in the train. If all vehicles were being retarded alike, there would be no change in the slack between cars, and all of the slack indicator diagrams would be horizontal lines. As a matter of fact, however, as soon as the steam is shut off, the retar- dation on the locomotive when drifting is greater than that of the cars. Consequently, the locomotive holds back against the train, bunching the slack most at the head end of the train and less toward the rear. This is well illustrated in Figs. 131 and 136, and the action is similar in all cases. When the brakes are applied, in all cases except when the electro-pneumatic emergency application is used, the effect o t brake application is first felt on the locomotive, causing a further running in of slack, as shown by the more or less abrupt rise in the slack indicator diagram taken between cars Nos. 1 and 2. 418. It is to be noted that the slack indicator diagrams show merely the relative movement between cars. This relative movement is, of course, brought about by the different rates of retardation on the dif- ferent cars in the train, which may or may not produce more or less severe shocks, depending upon whether the action takes place slow y or suddenly. The speed of this movement is shown by the abruptness of the rise or fall in the slack action curves. Consequently, a con- siderable amount of slack action may be shown by the diagram, in i cating a considerable difference in rate of retardation at different points in the train, but if these differences are brought about gradually, there may be little or no shock noticed. On the other hand, a much sma er amount of movement between cars, if taking place suddenly, as shown by the more nearly vertical line on the slack action curve, might e