Brake Tests

200 Stop distance of locomotive S1. Stop distance of single car S.. Number of cars N = 12. 411. For example, from the data of the best stops with the No. 3 clasp brake, flanged shoes, single car breakaway tests, we have: Wc = weight of car = 125,200 pounds. 12 Wc = 1,502,400 pounds. W1 = weight of locomotive = 414,800 pounds. Wt = W1+12 W.= 1,917,200 pounds. St = 1,552 feet, stopping distance of locomotive alone from a speed of 60 m.p.h. Sc = 991 feet, stopping distance of single car alone at 90 per cent, braking power from a speed of 60 m.p.h. Substituting these values in the following expression:— AW.S.S' - S. W1+S, 12 W. 1,917,200 X 991 X 1,552 We have 991 x 414,800+ 1,552 X 1,502,400 $= 1,075 feet. 412. Where the special high pressure emergency by-pass valve was used with the standard ET equipment on the locomotive, a shorter stop was obtained and in order to work out the train stop according to the above formula for this condition it would be necessary to substitute for the value of S, = 1,552 feet, the value of S =1,228 feet, which was the average stopping distance of the locomotive from a speed of 60 m.p.h. when using the special high pressure emergency by-pass valve. 413. The data of the best single car breakaway stops made with the No. 3 clasp brake from a speed of 60 m.p.h. at various percentages of braking power, with both plain cracked and flanged cracked shoes, are shown in Fig. 115. Using this data as a basis and combining with it the data of the separate locomotive tests, complete train stops were computed as described and have been plotted in Fig. 116. It will be noted that for each type of shoe two curves are shown. In each case the dotted and solid lines represent the train stops which would be obtained if the locomotive were operated respectively with or with- out the special high pressure emergency by-pass valve. The difference between the solid line and the dotted line for the corresponding brake shoe condition shows directly the effect of the difference of using the locomotive with or without high pressure on a twelve car train. 414. Fig. 116 is also of interest in that it shows the gain from the use of flanged instead of unflanged shoes. The best single car break- away stop with flanged shoes from 60 m.p.h. and 180 per cent, braking power was 725 feet. This is equivalent to a twelve car train stop, using the standard ET locomotive equipment, of 795 feet (Fig. 116).