Brake Tests

92 Electro-Pneumatic Equipment. 196. With the electro-pneumatic equipment a simultaneous and almost instantaneous application of the brakes in the train is obtained. The valve mechanism on each of the cars causes the brake cylinder pressure to rise to its maximum as quickly as the physical limita- tions of the air brake and foundation brake gear installation as a whole will permit and the maximum cylinder pressure thus obtained is maintained without blow-down (Fig. 56). Thus, by means of the electro-pneumatic control, an ideal emergency application of the brakes is obtained. 197. It should be noted that the only difference between the UC pneumatic and electro-pneumatic emergency application is in the elimi- nation of the time element in starting the application of the brakes on the various cars in the train. That this is an important gain, is shown by the fact that the emergency stops with the electro-pneumatic brake were from 200 to 275 feet shorter than with the pneumatic equipment. 198. The electro-pneumatic emergency stops are from 350 to 550 feet shorter than those obtained with an emergency application of the PM equipment. Furthermore, the very short stops made with the electro-pneumatic equipment were accompanied by the absolute elimi- nation of shocks, due to the action of the brakes, except in so far as the effect of the locomotive brake differed from that of the brake on the cars The effect of the locomotive was the only reason why the emergency stops with the electro-pneumatic brake were not absolutely without shock even at speeds as low as ten miles per hour. GENERAL COMPARISON OF EMERGENCY APPLICATIONS. PM AND UC Equipments. 199. Fig. 57 shows the data from the same brake cylinder cards as plotted in Figs. 53, 55 and 56, but in this case plotted to show the rela- tive time to start an emergency application of the brakes and the time to obtain full emergency brake cylinder pressure with the PM equipment, and the UC pneumatic and electro-pneumatic equipments. The rapid and uniform rate of application of the electro-pneumatic equipment is very clearly shown by the curve when compared with the longer time required to start the application of the brakes and to reacli the maxi- mum brake cylinder pressure, especially toward the rear end of the train when using the PM equipment. It will be noted that the UC equipment operating pneumatically was somewhat slow in starting compared with the PM equipment and that although it reacned its maximum pressure in about one-half the time required by the PM equipment on the train as a whole there was about three seconds re- quired to transmit the quick action from the head to the rear end of the train. This action of the valve when operating pneumatically