Two distinct characters of performance of the triple valve may thus occur, the selection of which is dependent wholly upon Lhe rate at which the air pressure in the train brake-pipe is reduced for applying the brakes. The measure of the greatest rate at which the pressure in the train brake-pipe may be reduced, without operating the supplementary parts of the new triple valve, is that rate at which the pressure is reduced in the auxiliary reservoir, by the flow of air therefrom to the brake-cylinder—which latter is determined by the size of the passage connecting them. A rate of reduction of the air pressure in the train brake-pipe, materially greater than that of the reduction of pressure in the auxiliary reservoir, will induce the quick action of the nearest triple valve, which will be eommunieated to all the others, producing a full application of all the brakes ; any rate, not greater, will cause the triple valves and brake apparatus to act in exactly the same manner as in the plain automatic brake, permitting the application of the brakes with any desired degree of force. To operate the quick-action automatic brake, greater precision is therefore involved than the plain au tomatic brake required, and a modi fied engineer's brake-valve is used for this purpose. The essential features .of the quiek-aetion automatic brake, differing from those of the plain au tomatic brake, thus lie wholly within the triple valve and engineer's brake valve. While the end primarily sought, iu the production of the quick-action automatic brake, was to avoid injurious shocks to the train, through application of the brakes, another result, of great importance, was incidentally effected, by causing the air, discharged from the train brake pipe through the triple valve, to pass into the brake-cylinder and to be retained there. This discharge of air from the train brake-pipe takes place before any considerable quanti ty of air can flow from the auxiliary reservoir to the brake-cylinder : the quantity of air discharged front the train brake-pipe is therefore depend ent upon the relative volumes of the brake-cylinder and that portion of the train brake-pipe attached to the ear. These relative volumes are such that the discharge of air from the train brake-pipe into the brake-cylinder, added to that from the auxiliary reservoir, inereases the final pressure in the brake-cylinder and upon the piston 20 per cent beyond that when the cylinder receives air from the reservoir alone. Thus, in addition to preventing injurious shocks to the train, the quick-action automatic brake attains a considerably greater degree of efficiency by produc ing, almost simultaneously, upon all the ears of the train the greatest permissible retarding foree, The Triple parts which have been added to those of the plain automatic triple valve are the piston S (Fig. 1); the valve 10—which, normally, is held upon the seat 9 by the spring 12, and which is operated by the piston b; and the cheek-valve 15, seated in the check-valve ease 13. The port t is added to the plain automatic triple valve, which, when uncovered by the slide-valve 3, affords communication between the auxiliary reservoir and the chamber above the piston 8. This port is not in line with the ports leading respectively to the brake-eylinder and the atmosphere, but is at one side. The slide-valve 8 is made longer than in the plain automatic triple valve, and a corner is cut away, so that, when the piston 5 moves to its extreme position at the right. the slide-valve uncovers the port t, and air from the auxiliary reservoir is admitted to the chamber containing the piston 8.
The operation of this triple valve is as follows: The auxiliary reservoir having been filled with air aL the pressure in the train brake-pipe, the brake may be applied by reducing the pressure in the train brake-pipe. The piston 5 moves to the right until stopped by the stem
21, and air begins to flow from the auxiliary reservoir to the brake-cylinder through the ports re, z, r, and c. the pressure in the train brake-pipe is not reduced at a more rapid rate than that at which the pressure falls in the auxiliary reservoir, no further movement of the piston 5 takes place ; if, however, the pressure in the train-pipe is rapidly reduced, the greater pressure in the auxiliary reservoir will force the piston 5 to its extreme position at the right, compressing the spring 22, and causing the slide-valve to uncover the port t. The pressure of the air thus admitted from the auxiliary reservoir upon piston 8 forces it down ward, unseating valve 10, and so permitting the air in the train brake-pipe to lift the check valve 15, and discharge directly into the brake-cylinder; the cheek-valve 15 then immedi ately closes and prevents the return of any air to the train brake-pipe. In this position of the slide-valve, also, the air continues to flow through the ports S and r from the auxiliary reservoir to the brake-cylinder until their air pressures come into equilibrium. As the spring 22 may be compressed by a comparatively small difference in the air pressures upon the sides of the piston 5, a small reduction only of air pressure in the train brake-pipe, if quickly made, occurs before it is given access to the brake-cylinder through the check-valve 15. In all other respects the quick-action triple valve operates in the same manner as the plain automatic triple valve, The triple valve is secured to and communicates directly with the auxiliary reservoir, while the pipe b, passing through the reservoir, affords communication between the triple valve and the brake-cylinder. The piston-rod 3 is a hollow tube, in which is inserted a rod having a clevis at its outer end, which is attached to the lever. Its out ward movement applies the brake.
The Engineer's Brake- ralre. —This valve has four distinct functions: First, to establish di rect communication between the main storage reservoir and the train brake-pipe, for releasing the brakes; second, to maintain the required air pressure in the train brake-pipe and auxiliary reservoirs, while also maintain ing a certain greater pressure in the main reservoir, to make sure the release of all the brakes after an application ; third, to permit the escape of air from the train brake-pipe at a fixed rate, for all ordinary applications of the brakes; fourth. to cause a rapid discharge of air from the train brake-pipe, to secure the quick-action in an emergeney application of the brakes. Figs. 2, 3, and 4 illustrate the brake-valve. The pipe from the main reservoir is attached at X; the train brake-pipe at I"; at 'Pa small reservoir is at tached, which merely serves the purpose of giving increased volume to the chamber B. A rotary valve 1:1 (the Imver face of which is shown in Fig. 81 is Operated by the handle 8.
The piston 17, having a stem formed into a valve at its lower end. is subject to the air pressure of the train brake-pipe upon its lower face and to the air pressure of chamber D upon its upper face. The rotary 13 has two ports, a and j, passing through it. and two cavities, c and h, in its lower face. The seat for valve 1:1 has a cavity 6, a large port k 111111 it small port It, both leading directly to the atmosphere. two ports, e and g, leading to the ehamber 1), a large port 1, leading to the train brake-pipe, and a port, f, leading to the port /, and in whirl is a valve 21. The different positions for the handle 8 are defined by projec tions from the valve-easing, shown in which are encountered by the spring 11 from the handle, and offer sufficient resistance to the movement of the handle to mark the positions.