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

Copyright, 1909, by The Norman W. Henley Publishing Co.

in the reduced brake pipe; it will be recalled that in response to a 10-pound brake-pipe reduction the pressure built up in the brake cylinder should be about 25 pounds, if the piston travel is correct; but in this arrangement there is no variable-traveling piston that can alter the result of the pressure expansion, and following a 10-pound reduction the application chamber will have 25 pounds pressure; this 25 pounds acting upon application piston 10, in application cylinder G, will force it to the left, unseating valve 5 and permitting main-reservoir air from chamber a to enter chamber b and pass from there to the brake cylinders of the engine and tender; and when-regardless of what distance the pistons may travel in the brake cylinders —their pressures become 25 pounds, or a very little greater, the same pressure being contained in chamber b, there is an equalization of pressure on piston 10, and the spring reacting upon valve 5 closes it and pressure supply to the brake cylinder ceases-until the pressure of chamber b and the brake cylinders begins to reduce through leakage, whereupon the greater pressure in application cylinder G again unseats the application valve, 5, and the brake cylinders are resupplied up to equalization, when the valve is closed as before. This automatic pressure-maintenance will be continuous as long as the charge remains in the application chamber; but when an increase of brake-pipe pressure moves