Brake Tests

111 245. As an average for the train as a whole the time of commencing the application, the rate of rise of brake cylinder pressure and the amount of and time required to obtain maximum pressure are sub- stantially the same as for the valves used during the road tests but the action of the individual valves is more uniform and consequently the operation on the train as a whole is correspondingly improved. Electro-Pneumatic Equipment. 246. Fig. 43-A compared with Fig. 43, shows the improved action accomplished by so constructing the valves that the rate of fall in auxil- iary reservoir pressure and consequently building up of brake cylinder pressure cannot gain on the established rate of brake pipe reduction. Fig. 43 shows that several of the valves momentarily lapped when approaching the maximum brake cylinder pressure, resulting in a considerably lengthened and non-uniform time of obtaining maximum service brake cylinder pressure. The desirable uniform rise of brake cylinder pressure is shown in Fig. 43-A. 247. While it may be thought at first glance that the action of the valves on different cars is not as uniform with the improved valves (Fig. 43-A) as for the valves used during the test (Fig. 43), this differ- ence is apparent rather than real. It is well known that the condi- tion of the individual valves with respect to lubrication, fit of moving parts, etc., will always change slightly the sensitiveness of the response of the valves to brake pipe reductions. In the case of the test shown in Fig. 43 all of the valves (except that of car nine) were responding almost identically during the first stages of the brake application. But the same valves under similar conditions acted quite differently in the case of the test illustrated in Fig. 51 where cars one and three responded more promptly than the remainder. Referring now to Fig. 43-A, it will be seen that there is not as much variation in the action of the different cars in the train in this case as is shown in Fig. 51. 248. Moreover, it is a matter of common experience and it was demonstrated several times, during the progress of the tests that valves departing slightly from the average uniform action of the other valves in the train as was the case for cars five and eight (Fig. 43-A), could invariably be brought into agreement with the other valves by simply cleaning and lubricating the mechanism. This could have been done in the case of the laboratory tests under discussion and the indicator cards shown on Fig. 43-A for the different cars would then have been almost identical. But it was thought better and more representative to take the valves in their ordinary condition without any special inspection or test and let the results come where they would.