Engineering Wonders of the World
Volume I

RAILWAY BRAKES. 247 All the brake cylinders are connected by flexible hose pipe to the train pipe, which runs from the engine to the rear guard’s van. On the engine is an air eiector, Air Ejector. . . the principle or which is ex- plained by a simple diagram (Fig. 3). Steam from the boiler enters by pipe C, and issues through a nozzle, B, into a larger nozzle, wherein the velocity of the moving steam creates a vacuum. Air rushes in from the train pipe through D until the pipe is entirely exhausted, or so far exhausted as slight leakage at joints in the pipe permits. The ejector actually used consists of two ejectors, known as the “ large ” and the “ small,” the second being placed inside the first. The small ejector is worked continuously, the large one only when it is necessary to release Fig. 4.—ARRANGEMENT OF CYLINDER, LEVERS, RODS, AND BRAKE SHOES ON PASSENGER COACH. The arrows show direction in which the rods move to apply brake. When a train has to be restarted after a stop, the driver, by means of the ejector, draws the air from the train pipe and vacuum chambers. The air is sucked directly from the under side of a brake piston through the pipe D (Fig. 1), and from the space AA and the upper part of the cylinder through the channel C, the ball valve keeping open until exhaustion is complete or the pressure the same on both sides of the piston, when the ball falls back on to its seat. When air is admitted into the train pipe, it rushes into space B unchecked, but is pre- vented by the ball from reaching AA. Con- sequently a strong upward pressure is ex- erted on the under side of the piston, and the brake goes on (Fig. 2). As the largest brake pistons have an area of some 340 square inches, a difference of 10 lbs. per square inch between the pressures above and below a piston of that size gives a direct pull of about a ton and a half. A suitable arrange- ment of levers (see Fig. 4) increases this pull ten times at the brake blocks. On a very long train the destruction of the vacuum in the train pipe by from one point only would not be effected quickly enough to meet sudden emergencies. In the guard’s van there is installed an in- admitting air Guard’s Van Valve. be opened at any time by pressing down a lever, E, but which opens of itself when the train pipe vacuum is destroyed rapidly. Seated on the top of an upright pipe is a valve, A.