Brake Tests

288 referred to, it will be noted that the efficiency of the rigging at 150 per cent, braking power is 83.2 per cent, which means that the actual brak- ing power at the shoe will be 150 X 0.823 = 123.45 per cent. Referring to Fig. 170, it will be seen that at 123.45 per cent, braking power the curve representing the results of machine tests of slotted flanged shoes gives a value of 603 feet as the stopping distance. Now applying the ratio or difference factor 1.265 (Par. 552) the actual stop of the car will be 603 X1.265 =763 feet at the actual braking power of 123.45 per cent, or at a nominal braking power of 150 per cent. 554. It must be borne in mind that in the example given above the brake application on the road is assumed to be an electro-pneu- matic emergency which requires an average time from point of trip to maximum cylinder pressure of about 2.25 seconds. The time to point of equivalent instantaneous application of brake is 0.75 second. The ratio given for the machine test results is for this same time of applica- tion. If it is desired to use this factor for any other brake application with a different time to point of equivalent instantaneous application, then the difference in time must be multiplied by the initial speed in feet per second of the car and this difference added to or subtracted from the distance (763 feet mentioned above) depending upon whether the time is greater or less. CONCLUSIONS. AIR BRAKE. 1. The introduction into service of cars with UC equipment will result in an improvement in the handling of trains (Par. 201) and is advisable for the following reasons: (a) In service applications a greater flexibility is provided by the UC equipment than by the PM equipment. (Pars. 121 and 122.) (b) Because of the respective sizes of reservoirs used a greater reduction of brake pipe pressure to obtain the same braking power is required with the UC equipment than with the PM equipment. A longer time is available in which the engineman can judge the rate of retardation and thus has better control of the speed of the train. (Par. 123.) (c) In release the UC equipment is more sensitive and more prompt than the PM equipment. (Par. 227.) (d) The presence of UC equipment mixed with the PM equip- ment in the same train results in an improvement in the release action of all the brakes. (Par. 237.)