Зображення сторінки
PDF
ePub

Automatic Release

the intermediate; and as the piston travel on all cars in the train is not known to the engineer, when a fullon service application is to be made it is necessary to reduce the brake-pipe pressure 25 pounds.

OPERATION OF BRAKE RELEASE: As the reduction of brake-pipe pressure influenced the triple valves to cause an application of the brakes, it is through the medium of the brake-pipe air that the engineer releases them, which he does by increasing the pressure; but, whereas an automatic application of all brakes may be made at any point in the train by reducing the brakepipe pressure, the engineman, only, can automatically release them, as the main reservoir carrying the high releasing-pressure of great volume is located on the engine; if, however, it is required to release brakes on cars that are detached from the engine, or in case of a very long train when the main reservoir may not be pumped-up to a pressure sufficiently high to release all brakes, those remaining applied are said to be "stuck," and can be released by the trainmen" bleeding" each one individually.

To automatically release the brakes, the engineer's brake-valve is placed in the release position which permits the high pressure of the main reservoir to flow to the brake pipe, and the increased pressure entering the triple-valve chambers, p, p, becomes higher than that of the auxiliary reservoir, and piston 26 will be

moved its full traverse to the left, to the Release and Charging Position as shown in Fig. 4 A, in which feedgroove u is open, through which brake-pipe air begins recharging the auxiliary reservoir; cavity k in the face of slide-valve 31 now connects port h with the exhaust port in the slide-valve seat, thus opening a way for the brake cylinder pressure, flowing back through the tube L, to escape to the atmosphere, after which, the large releasing spring around piston rod 12 pushes brake piston 10 to its release position, as shown, against the pressure head of the cylinder.

To bleed the brakes, the trainman opens the release valve (not shown) on the auxiliary reservoir, thus reducing its pressure until it is less than that of the brake pipe when the triple valve will be moved to release position in the same manner as explained in reference to automatic release, and by the same reason -i.e., the brake-pipe pressure is become greater than that of the auxiliary reservoir; but, to effect the release in this way, the auxiliary reservoir of every applied brake in the train must be individually “bled”; if no pressure remains in the brake pipe, the triple valve will be moved to the position shown in Fig. 4 B by the force of the graduating spring when the auxiliary pressure has been largely reduced by bleeding, after which the brake-cylinder pressure will flow back into the auxiliary reservoir through tube L and ports h

Release by “Bleeding' and 2, and to the atmosphere through the release valve; in the latter case, the release valve must be kept open until all of the pressure in the auxiliary reservoir and brake cylinder has been discharged.

RUDIMENTS OF THE DISTRIBUTING VALVE.

Owing to its automatic character, the unimproved air-brake can not be depended upon to stay applied for any considerable length of time, as the auxiliary reservoir—the local base of pressure supply—is cut off from recharge by the act of applying the brake, and the inevitable piston packing-leather leakage may be expected to waste away the air from the brake cylinder and auxiliary reservoir; but the locomotive—the heaviest unit of the train, and equipped with a brake equaling in calculated power the brakes of several modern freight cars-carries the main-reservoir pressure, and in the E-T type of locomotive-brake equipment a way has been found to supply pressure to the engine and tender-brake cylinders directly from the main reservoir and yet to retain the automatic action and brakepressure-graduation in harmony with the triple-valveoperated cars of the train.

The distributing valve is the central figure of this new equipment, and before taking up the description and explanation of its mechanism in technical detail, a diagrammatic figure will be used to exemplify the principle on which the brake-cylinder pressure is supplied and the automatic graduation of same is performed. In Fig. 5, we have a triple valve precisely similar to

Rudiments of Distributing Valve

the one described, but here denominated the equalizing valve, an auxiliary reservoir changed in name to pressure chamber, and a sealed vessel containing the same volume as would be in the pressure end of the brake cylinder of Fig. 4 A with the brake piston moved out to its normal travel, but called the application chamber; and these, with the addition of the case containing the small piston and valve at the left of the application chamber, constitute the application features of the distributing valve in an ideal form.

The same explanation as given of Figs. 4 A, 4 B, 4 C, and 4 D will apply to the action of the equalizing valve as the result of brake-pipe pressure reductions and recharge; full main-reservoir pressure enters and is contained in chamber a, as indicated, and serves to hold application valve 5 seated; from chamber b, a pipe leads and branches to all brake cylinders of the engine and tender; therefore, application piston 10 has whatever pressure may be in the locomotive-brake cylinders on one side of it, and the pressure of the dummy-brake cylinder, or application chamber, on the other side.

If a brake-pipe reduction of 10 pounds should be made, the equalizing valve operating as a triple valve will permit air to flow from the pressure chamber to the application chamber until the pressure of the former has been also reduced to a fraction less than that

« НазадПродовжити »