Brake Tests

85 Electro-Pneumatic Equipment. 185. For the electro-pneumatic equipment as explained in the pre- ceding paragraph for the pneumatic equipment, the results of an emer- gency following a full service application (Fig. 51) are similar to those of an emergency following a partial service application, except for the addi- tional time and length of stop corresponding to the longer time during which the service application was continued before the emergency application was made. 186. With an emergency application following a full service the length of stop is about 150 feet longer than when following a partial ser- vice application, but about 340 feet shorter than when only a full service application is made and over 400 feet shorter than a full service appli- cation with the PM equipment with which the making of an emergency application thereafter has no effect on the length of stop. 187. As a matter of interest a composite brake cylinder card and deceleration curve is shown on Fig. 52 for the PM and electro-pneu- matic equipment full service application followed by an emergency appli- cation. The curves show clearly the more quickly obtained service brake cylinder pressure with the electro-pneumatic equipment and the quicker and more effective brake cylinder pressure obtained when an emergency application was made. What resulted from this is shown in the more prompt rise of and the higher value reached by the decel- eration curve for the electro-pneumatic equipment and tlie correspond- ingly shorter stop obtained. 188. Figs. 46 to 52 are important as they demonstrate that with the UC equipment operating either electrically or pneumatically the engineer has available for use in any emergency that may arise a quick acting and fully effective emergency brake, no matter what manipu- lation he may have made previously. The additional safety factor insured by this means as compared with the absence of any such safety factor with the PM equipment is proportional to the difference in the stopping distance already discussed. (Par. 186.) Emergency Application. PM Equipment. 189. Fig. 53 shows characteristic brake cylinder indicator cards for PM equipment emergency applications. The rate of rise of brake cylinder pressure is slightly faster and the maximum pressure obtained slightly higher than would ordinarily be the case on account of the larger size of auxiliary reservoirs used. 190. The characteristic blow-down action of the high-speed reducing valve is clearly shown by the shape of the curves. The cyl- inder pressure is reduced from an average of about 78 pounds at the beginning to nearly 60 pounds at the end of the stop.