Brake Tests

291 equipment from service applications when not desired; for with the new design of brake, it requires a four-pound drop in brake-pipe pressure to start movement of the valve, whereas, with the PM equipment, which is subject to over sensitiveness to unavoidable fluctuations in brake- pipe pressure, a differential of only two pounds is required. Therefore, this decreased sensitiveness in service applica- tion minimizes the effect of fluctuations in brake-pipe pressure, which cause undesirable applications. (d) The time of transmission of serial quick action through the brake pipe is practically the same with the UC as with the PM equipment. (Pars. 194, 251.) (e) When using the same size service reservoirs with PM and UC equipments, while it will take somewhat longer to start a service application with the UC equipment than with the PM equipment. After starting, the UC equipment builds up brake cylinder pressure at a rate substantially the same as the PM equipment. Our experi- ments with mixed trains in which the PM cars had large size reservoirs indicate that there was no undesirable difference in the action upon the various cars. (Pars. 160 to 165.) (Pars. 225 to 233.) (f) With the PM and UC equipment, the time of starting an emergency application on the first car, on all cars, and the time to attain maximum brake cylinder pressure on a 12-car train is as follows: . UC Pneumatic------ UC Electro-Pneu-[ matic________—) Brakes Start to apply on MAXIMUM BRAKE cylinder PRESSURE ATTAINED 1st CAR All cars Less than 0.5 Sec Less than 0.5 Sec Less than 0.5 Sec 2 ) 2 Secs.. .< 1.5 Secs.. Less than 0.5 Sec. - 8 Secs. Fig. 57. Page 94. 3.5 Secs. Fig. 57-A. Page 118. 2.25 Secs. Fig. 57-A. Page 118. Equipment PM From the foregoing there is a gain in time in reaching maximum brake cylinder pressure on all cars of 56 per cent, for the UC pneumatic over the PM equipment, and when the UC equipment is operated electrically a gain of 72 per cent. In this feature the UC equipment shows a remarkable gain over the PM equipment, and this is the predominating advantage so far as shortening the stop is concerned. As a further advantage with the UC equip- ment, emergency brake cylinder pressure is held without blow down towards the end of the stop (Fig. 55), whereas