Engineering Wonders of the World
Volume I

Vgcuum Chamber Fig. 1.—SECTION OF VACUUM BRAKE, CYL- INDER, PISTON, VALVES, ETC. BRAKE OFF. Fig. 2.—SECTION OF VACUUM BRAKE, CYLINDER, ETC., WITH BRAKE ON. RAILWAY BRAKES. THE remarkable freedom from serious accident and loss of life which dis- tinguishes modern railway working is due not less to the efficiency of the auto- matic brakes fitted to rolling-stock than to the perfection of signalling apparatus and organization. At the present day one or other of two systems is used on practically all automatic- ally-braked wagons and coaches. These are known as—(1) the Vacuum Automatic, using the pressure of the atmosphere on one side of a piston from the other side of which the air has been exhausted mechanically ; and (2) the Westinghouse Automatic, using compressed air. In both cases the mechanical arrangement ensures that the brakes (a) must be kept “off” artificially; (&) shall apply themselves automatically should the train part by accident; (c) can be applied with greater or less force as circumstances may require. The action of the two systems will be explained as simply as possible. To begin with The Vacuum Automatic Brake. Under each carriage is a vacuum chamber (shown in section in Figs. 1 and 2), riding on trunnions, EE, which are able to swing in sockets attached to the body of the vehicle. Inside this is a cylinder, the upper end of which reaches almost to the top of the cham- ber. A long piston, rendered air-tight by a rubber ring rolling between it and the cylinder walls, works up and down in the cylinder, carrying with it a piston rod, which projects through an air-tight stuffing-box in the bottom of the casing, and operates the brake rods. It is obvious that, if air be exhausted from both sides of the piston, the last will sink to its lowest position (as seen in Fig. 1) by reason of its own weight and that of its attachments. If air be admitted below the piston, the piston will be pushed upwards with a maximum pressure of 15 lbs. to the square inch (Fig. 2). The ball valve ensures that, though air can be sucked from both sides of the piston, it can be admitted to the lower side only.