Brake Tests

75 General Comparison of Service Application—PM and UC Equipment. 169. Fig. 44 shows data from the same brake cylinder cards as plotted in Figs. 41, 42 and 43, but in this case plotted to show the relative time to start the application of the brakes and the time to obtain full brake cylinder pressure with the PM equipment and the UC pneumatic and electro-pneumatic equipment. The quicker and more uniform appli- cation of the electro-pneumatic equipment is still more clearly brought out by these curves. It will be noted that the time to reach full brake cylinder pressure on cars 4, 5, 9 and 10 with the electro-pneumatic brake are considerably longer than on the remainder of the train, which seems to contradict the statements previously made with regard to the uniformity of the action of the electro-pneumatic equipment. This is explained, however, when it is noted that these cars 4, 5, 9 and 10 are the ones which (Fig. 43) suffered a delay in the latter part of their application due to a more prompt build-up of brake cylinder pressure than on the other cars during the beginning of the application, which was followed by an automatic lapping of these valves, resulting in a slower rise to maximum brake cylinder pressure. This action was caused entirely by the mechanical operation of the mechanism. While it was not sufficiently great to be detrimental in any way, it was not desirable and the operation of the valve in this particular was subsequently improved by a slight modification of the mechanism. (Par. 242.) Partial Service Followed by Emergency Application. PM Brake Equipment. J70. Fig. 45 sliows the results obtained with the PM equipment when a partial service brake application is made followed immediately by the movement of the brake valve handle from service to emergency position. 171. It is important to note in the first place the way in which the triple valves began to respond to the reduction in brake pipe pressure compared with the action shown in Fig. 41. The same type of triple valves were used, but the applications were on different days, being for Fig. 45 February 13th and for Fig. 41 April 23d. There is as much difference between the time of starting to apply the P triple valves (Fig. 41 and Fig. 45), as between the P triple valves and the universal valve of the UC equipment (Fig. 41 and Fig. 42). All these examples show that the condition of the triple valve (which is a variable depending upon many things such as the weather, the lubrication of the valves; the amount of use they have had and so on) causes considerable variations in the results. I72. It is barely possible to distinguisli signs of the emergency appli- cation from the shape of the curves of Fig. 45 when compared with a