Brake Tests

167 374. The series of check runs also confirms previous observation that the length of stop, when considerable wheel sliding occurs, is invar- iably longer than when sliding does not take place. This will be clear from the data plotted in Fig. 89. The only exception to the above is in the case of test No. 501, which was the first test of the series and for which the shoe condition was known to be unsatisfactory. 375. The average of the check runs of No. 1 clasp brake having material wheel sliding, is 1,353 feet. The average check run compar- able with this, but without material wheel sliding is 1,204 feet, show- ing an increase in the length of the stop of twelve per cent. Check Runs with Single Cars, No. 2 AND No. 3 Clasp Brakes. 376. The No. 3 clasp brake was applied to but one car. Check runs were made with this car, and with a single car having No. 2 clasp brake under the same conditions as for the twelve car train check runs, excepting that the car was separated from the locomotive before reach- ing the trip, so that the stop of the car alone might be observed. All the stops so obtained are plotted in Fig. 91 for No. 2 clasp brake and Fig. 92 for the No. 3 clasp brake, the distance of stop being plotted for the actual per cent, braking power based on brake cylinder pressure obtained in each test. Averages. 377. The summary and averages of tests are given on pages 300 to 317. In this summary is shown all the tests made, grouped by desig- nation. The average is taken of those tests of a series which were considered representative runs. 378. The tests of a series which were not included in the average are shown as a matter of record. These tests have been excluded due to the existence of one or more important variables as indicated on the graphical log for the respective tests. These variables appear to have affected the results and did not enter into the other tests run in that particular series. 379. The following factors have been considered of sufficient weight to exclude a test from the group averaged as not representative. A.—Failure of any part of the brake rigging. B. —Undesired operation of air brake equipment due to:— (a) Electric emergency interfered with by damaged jumper caused by severe treatment in breakaway tests. (b) High-speed reducing valves not properly cut in or out. (c) Brake cut out when not intended or due to failure of some portion of rigging. (d) Brake pipe pressure different from the normal required by the designation.