Brake Tests

105 cars 7, 8 and 9 when the release was attempted after the first appli- cation (Fig. 64). The brake pipe pressure, as indicated by the record taken on car 6, was increased by a slight amount (about 3 pounds) when releasing from the first application, and preparing for the second application. This slight increase in brake pipe pressure released the three PM equipments and the three UC equipments in the first half of the train. The three UC equipments at the rear of the train were also released. But the PM equipment on cars 7, 8 and 9 failed to release. 227. This is a clear demonstration of the fact that the UC equip- ment was more sensitive to release (as it was designed to be) than the PM equipment. In other words, the UC equipment on the three cars at the rear end released on a slight rise in brake pipe pressure which was not sufficient to release the PM equipments on the three cars preceding. These PM equipment cars, so far as the brake pipe pressure was con- cerned, were more favorably placed than the three UC equipment cars at the rear end which did release. 228. It is important to note that this stop was without any roughness or shock even though the braking power was considerably higher on some cars than on others. But as will also be evident from the indicator cards (Fig. 64), this difference in pressure was set up gradually and because of this the readjustment of slack took place gradually which means that no shocks or roughness could result. STATION Stop. 229. Mixed equipment on cars as follows:— Car Nos.......1 2 3 4 5 6 7 8 9 10 11 12 Equipment. . PM PM PM PM PM PM UC UC UC UC UC UC 230. This arrangement of equipments was tried to determine the action of the train when making a service stop with first half of the train having PM equipment, the last half UC equipment. A two- application stop was made (Fig. 65) and nothing unusual in the action of the equipment or the riding of the train was noticeable. 231. This make-up was as likely to produce shocks as any that could be devised but after the initial adjustment of the slack, which resulted in two or three slight jars, the remainder of the stop was smooth. Station Stop. 232. Mixed equipment on cars as follows:— Car Nos.......1 2 3 456 7 8 9 10 11 12 Equipment UC UC UC UC UC UC PM PM PM PM PM PM 233. The arrangement of UC and PM equipments in this stop (Fig. 66) was the reverse of that just explained for Fig. 65. A full service brake application was made and no unusual action of any Sort was observed during this test and the stop was made without shocks.