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BY INDEPENDENT BRAKE-VALVE.
Attention will now be given to the effects from the operation of the engineer's INDEPENDENT BRAKEVALVE, first, in applying the locomotive brake while the automatic brake-valve remains in running position, and secondly, the consequent position of independent lap taken by the distributing valve; followed by a description of the manner in which the driver and tender brakes may be released independently of the train brakes after all have been automatically applied, and while the automatic brake-valve remains on lap.
The first condition is represented in Figs. 15 A and 15 B-Independent Locomotive-Brake Application. Referring to the piping diagram, the automatic brakevalve is in running position, and all pipes supplied by it with pressure are charged as explained in its common, running position. The independent brake-valve handle has been turned to application position causing the reducing-valve pipe pressure to flow to the application-cylinder pipe, and through it in one direction to the automatic brake-valve where that pipe is blanked under the rotary valve, and to the distributing valve where it actuates the application mechanism (nearing
The E-T Air-Brake Pocket Book
the latter, the pipe is given the color of the applicationcylinder pressure); at the distributing valve the application-cylinder pressure fills the distributing-valve release pipe through which it only flows as far as the rotary of the independent brake-valve, being separated there, now, from its branch pipe connecting with the automatic brake-valve, the latter section of pipe being still open to the atmosphere through the rotary of the latter valve.
As the pressure of the reducing-valve pipe is being used as the actuating pressure, the check-valve in the fitting called “strainer and check-valve” prevents signalpipe pressure from returning and so reducing as to cause the air-signal whistle to blow.
The action of the distributing valve resulting from the supply of reducing-valve pressure will be to cause main-reservoir air to flow to the brake cylinders of the locomotive, as indicated in color on the piping diagram. The reducing valve is commonly adjusted at 45 pounds, and whether the independent brake-valve is permitted to supply the full amount or only a portion of that pressure to the distributing valve, the latter will give an equal charge to the brake cylinders. Other than as stated, the pressure conditions remain as characterized throughout the piping in the usual running position of the brake-valves. Referring to the distributing valve itself—Fig. 15 B
-it will be understood that the lower portion remains undisturbed, there being no reduction of brake-pipe pressure. The reducing-valve pressure, entering at II, passes directly to the application cylinder, g, and forcing piston 10 to the right, the operation of the application portion will be as usual in the cases heretofore described which should be generally understood by this time; the main-reservoir air from chamber a flowing to the locomotive brake cylinders through the brakecylinder pipe connecting at CYLS. The applicationcylinder pressure supplied from the reducing valve flows, via ports h, k, and w, to the application chamber which supplies the volume necessary in regulating a graduated application; through ports h, k, and i, it flows to the distributing-valve release pipe at IV; and through ports h, s, and I, the application-cylinder pressure also passes to the safety valve, which, in case the reducing valve should become defective and permit the full main-reservoir pressure to be supplied, would unseat itself and endeavor to reduce the excess of pressure over 68 pounds.
Independent Lap Position. The application portion of the distributing valve will take the lap position following a locomotivebrake application by the independent brake-valve in any degree of pressure up to the full 45 pounds sup
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plied by it from the reducing valve, for the reason that the braking air from the main reservoir is always at a higher pressure and will compel the lapping whenever the brake-cylinder pressure equals, or slightly exceeds, that in the application cylinder. The lapping movement of the application portion of the distributing valve is similar at all applications of the brake, and was explained in reference to Figs. II and 13; Fig. 16 shows it in the position of independent lap. It should be understood that this does not necessarily imply the lapping of the independent brake-valve—which latter would simply mean that the independent brake-valve had been so moved as to cut off the supply of reducingvalve pressure to the application cylinder.
In connection with this it should be noted that the equalizing portion of the distributing valve not having changed from its so-called release and charging position during the course of the independent application and resultant lap of the application valve, on that account the safety valve is still connected to the application cylinder in this position, and when it becomes necessary to hold the locomotive for some time with the independent brake-valve while standing, that brake valve should not be returned to the lap position, as a leak in the safety valve from scale or other obstruction between valve and seat would soon discharge the application-cylinder pressure and release the locomotive brake. Under the