Brake Tests

139 300. The tender of the second locomotive No. 5223—K2Ba, was equipped with a truck of the arch bar type, later replaced by one of the pedestal type, thereby increasing the weight from 74,600 to 82,450 pounds. In order to produce the standard braking power for this weight, the 12-inch cylinder which was on the tender required a total lever ratio of 14.6 to 1, which is considerably higher than is desirable for a single shoe rigging. The high lever ratio combined with a relatively large horizontal shoe movement resulted in excessive piston travel. 301. By replacing the 12-inch cylinder, which is standard for K2. tenders, with a 14-inch, the total lever ratio was reduced from 14.6 to 1 to 10.7 to 1, and by comparing the stop of the locomotive in breakaway tests before and after the application of the 14-inch cylinder (test 31), the increased effectiveness of the brake with lower lever ratio is apparent. 302. Diagramatic drawings of the locomotive and tender brake rigging are shown in Figs. 82 and 83, and the percentage of braking power for 50 pounds brake cylinder pressure is shown on page 321. Brake Rigging Requirements. 303. These tests have developed certain principles, most of which were known before the test, but their relative importance was not established until a satisfactory design of clasp brake had been developed and stops obtained, which were anticipated from the application of two brake shoes per wheel. The complete design of any brake rigging must be a compromise in which the relative values of each of the items herein enumerated have been given their proper consideration with respect to each other. (A) Precaution against accidents that may result from parts of the rigging dropping on the track. (B) Maximum efficiency of brake rigging at all times to insure the desired stop with a minimum nominal per cent, of braking power, thereby reducing to a minimum the cost and weight of brake rigging and air brake equipment. (C) Uniform distribution of brake force, in relation to weight braked, on all wheels, to insure the use of maximum retar- dation with minimum chances for wheel sliding. (D) With a given nominal per cent, braking power, the actual braking (which depends on the brake rigging efficiency) to remain constant throughout the life of shoes and wheels. (E) Piston travel to be as near constant as practicable under all conditions of cylinder pressure, to insure maximum stopping efficiency for emergency braking and desired flexibility for service braking at low speed. (F) Minimum brake shoe wear in doing a given amount of work in a minimum time.