Engineering Wonders of the World
Volume I

 248 ENGINEERING WONDERS OF THE WORLD. connected by a bolt, B, to an elastic diaphragm, C, sealing the bottom of the chamber D. A very small hole pierces B axially. When the vacuum is broken slowly, the pressure falls in D as fast as in the pipe ; but a sudden inrush of air causes A to be pulled off its seat by diaphragm C, above which the vacuum has not been broken to any appreciable extent. Air is thus given free access to the train pipe until the pressure in the last is that of the atmos- phere, then the valve returns to its seating. To hasten ap- plication of the brakes still fur- ther, a rapid-act- ing valve may be fitted to every coach. Fig. 6 gives sections of ° such a valve. It contains a RaPValvetinSr hinSed clappet, A, communi- cating with the outer air, and a valve, B, the stem of which, c, is attached to a rubber diaphragm, b. Between the fixed Fig. 6. peg a and the walls of c there is an annular passage, through which air can be admitted to the brake cylinder in quantities sufficient for ordinary applications of the brakes. When an emergency application is needed, air is admitted suddenly to the train pipe, and thus to the under side of valve B. This causes B to rise and allow air to pass full bore past A to the brake cylinder and train pipe, as shown in the diagram on the right. As soon as the brake is “ full on ” the valves resume their normal positions. By means of the lever with a hooked end the clappet can be held down, so as to make the brake “ ordinary ” instead of “ rapid acting.” The efficiency of the valve and brake is shown by the following figures relating to a test made with a freight train composed of one engine, twenty 30-ton bogie wagons, and a 10-ton van, having all wheels braked except those of the van, and weighing in all 380 tons 6 cwt. The length of brake piping was 1,053 feet, or about one-fifth, of a mile. On a down grade of 1 in 125 the train, travelling at 35 miles an hour, was brought up in 150 yards from the spot at which the driver applied the brakes. • T ests Time occupied in stopping, 25 seconds. At 40 miles an hour, on the same gradient, the distance and time of stopping were 260 yards and 26 seconds respectively ; at 32 miles per hour on an up grade of 1 in 185, 133 yards and 19 seconds respectively. It should be added that with loose coupled wagons the stop must be “ smooth,” and therefore re- quires a greater distance than would suffice for a close-coupled passenger train of equal weight. The Westinghouse Air Brake. This apparatus is somewhat more complicated than that just described—too complicated, in fact, to explain here in detail. We therefore have recourse to a few diagrammatic sketches which will make clear the general principles of the brake.