Brake Tests

71 158. The brake pipe reduction for this test was sufficient to insure the opening of all the high-speed reducing valves. That is to say, it was made heavy enough to apply the brakes to the maximum force they were capable of producing with a service brake pipe reduction rather than being made exactly 20 pounds, which is usually understood to be the technical meaning of the term “full service brake applications” with PM equipment. UC Equipment—Equivalent of PM and Complete Pneumatic. 159. Fig. 42 illustrates the action of botli the equivalent of the PM equipment and the UC pneumatic equipment when making a full service application of tlie brakes. The service features of these two forms of the improved equipment are identical. 160. Due to the service stability feature (Par. 124) of the UC equip- ment the brake cylinder pressure does not start to rise quite as quickly as with the PM equipment, but the time of obtaining an effective brake cyl- inder pressure is the same with the UC and PM equipments. The time to the beginning of rise of brake cylinder pressure is slightly longer for test 084 (Fig. 42) (UC equipment) than for test 034 (Fig. 41) (PM equipment), but reference to the indicator cards showing other service applications for the PM equipment (Fig. 45 and Fig. 49), will show that on account of the ordinary variations to be expected in the action of the type P triple valve, due to the condition of the mechanism it is likely to take just as long to start an application with the PM equip- ment as with the UC equipment having the service stability feature. Once having started, however, the UC equipment builds up pressure in the brake cylinder at a rate which is properly proportioned to the rate of brake pipe reduction. From this point on, it is similar to the action of the PM equipment installed on an equal basis. 161. The effect of the slight variations in sensitiveness of different valves is shown by the records from cars 1, 2 and 7 (Fig. 42), which started to apply at a more rapid rate than was in accordance with the rate of brake pipe reduction. This tendency was checked by the momentary automatic lapping of the valve mechanism, the rise of cylinder pressure thereafter being established at a uniform rate with that of the other cars. 162. Comparing Fig. 41 and Fig. 42, the effect of the different size reservoirs, used when making a service application of the brakes, as already mentioned (Par. 80 and 122), is clearly seen in the different slopes of the application lines. This results in the PM equipment (Fig. 41), reaching its maximum pressure in 12 seconds whereas, the UC equip- ment requires 16 to 17 seconds. These rates, it should be noted, are determined primarily by the rate of fall of brake pipe pressure which is relatively slow (pneumatic operation) on long trains because of the large brake pipe volume.