133. Q. Explain the movement of the parts in the distributing valve when the brake valve is moved to running position after having first been moved to release or holding position, following a brake application.
A. In this position of the brake valve the port to which the distributing valve release pipe is connected is open to the exhaust, thus allowing the air to escape from the application chamber and cylinder. The reduction of pressure in chamber "g", will allow the brake cylinder pressure in chamber "b" to force the application piston and its valves to release position, thus allowing the brake cylinder air to escape to the atmosphere, through the exhaust ports "e" and "d". (See Fig. 8.)
134. Q. Explain how an independent release of the locomotive brake is obtained after an automatic application has been made.
A. If the brakes have been applied throughout the train, by means of the automatic brake valve, and it is desired to release the locomotive brakes without releasing the train brakes, the handle of the independent brake valve is placed in release position. In this position of the independent brake valve, the application cylinder in the distributing valve is connected through the application cylinder pipe to the direct exhaust port of the independent brake valve; thus exhausting the air from the application cylinder, causing a release of the locomotive brake. This independent release of the locomotive brake does not cause the equalizing piston and its slide valve in the distributing valve to change their position.
135. Q. Explain what takes place when an automatic emergency application is made.
A. Any sudden reduction of brake pipe pressure is felt on the brake pipe side of the equalizing piston 26 and will cause it and the slide valve 31 to move to the extreme right, compressing the graduating spring 60.
(See Fig. 11.) In this position pressure chamber air can flow to the application cylinder only as the application chamber is now cut off.
This will cause a quick rise of pressure in the application cylinder, forcing the application piston and its valves to full application position, admitting main reservoir air to the brake cylinders and applying the brake. In emergency position of the automatic brake valve there is a small port in the rotary valve, called the blow-down timing port, through which main reservoir air is free to flow to the application cylinder "g" through the application cylinder pipe "II", causing a rise of pressure equal to the adjustment of the safety valve.
136. Q. At what pressure is the safety valve adjusted?
A. At sixty-eight pounds.
137. Q. What is the purpose of the quick action cap, and where is it located?
A. Its purpose is to a.s.sist the brake valve in venting brake pipe air when an emergency application of the brake is made, and is located on the brake pipe side of the distributing valve in place of the plain cap.
(See Figs. 8 and 11.)
138. Q. Explain the operation of the quick action cap.
[Ill.u.s.tration: Fig. 11. Emergency Position of No. 6 Distributing Valve with Quick-Action Cap.]
A. In an emergency application, the equalizing piston 26 moves to the extreme right, the k.n.o.b on the piston strikes the graduating stem 59, causing it to compress the graduating spring 46, and move the slide valve 48 to the right, opening port "j".
[Ill.u.s.tration: Fig. 12. Independent Application.]
Brake pipe pressure in chamber "p" flows to chamber "X", pushes down check valve 53, and pa.s.ses to the brake cylinders through port "m" in the cap and distributing valve body. When the brake cylinders and brake pipe pressures equalize, check valve 53 is forced to its seat by spring 54, thus preventing air in the brake cylinders from flowing back into the brake pipe. When a release of the brake occurs and piston 26 is moved back to its normal position, spring 46 forces graduating stem 59 and slide valve 48 back to release position.
139. Q. Explain the operation of the distributing valve when making an independent application of the brake.
A. When the independent brake valve handle is moved to application position, air is admitted from the reducing valve pipe through the application cylinder pipe to the application chamber and cylinder.
Pressure forming in the application cylinder will move the application piston 10 to the right, carrying with it the exhaust valve 16 and the application valve 5, closing the exhaust port and opening the supply port, admitting main reservoir air from chamber "a" to the brake cylinders (see Fig. 12) until the pressure in the brake cylinders and chamber "b" slightly exceeds that in chamber "g", when the application piston 10 and valve 5 will move back to lap position. By moving the brake valve handle to either release or running position, the air is exhausted from the application cylinder and chamber, thus reducing the pressure in chamber "g", allowing the pressure in chamber "b" to force the piston to the left, carrying with it the exhaust valve 16, opening the exhaust ports "e" and "d", allowing the air from the brake cylinders to escape to the atmosphere, thus releasing the brake.
DISTRIBUTING VALVE DEFECTS
140. Q. If the locomotive brake released with the automatic brake valve in lap position, where would you look for the trouble?
A. Would look for a leak in the application cylinder pipe or in the application cylinder cap gasket.
141. Q. If the brake remained applied in lap position, but released in release or holding position, where would you look for the trouble?
A. Would look for a leak in the distributing valve release pipe.
142. Q. If the distributing valve release pipe and application cylinder pipe were crossed, what would be the effect?
A. A brake application made by the automatic brake valve cannot be released by the independent brake valve.
143. Q. If the safety valve leaks, what will be the effect?
A. This may prevent the brake applying, and in an independent application if the brake does apply, it will release when the brake valve is returned to lap position.
BROKEN PIPES
144. Q. If the main reservoir supply pipe to the distributing valve breaks, what should be done?
A. Plug the pipe toward the main reservoir. The locomotive brake is lost, but if the distributing valve is equipped with a quick action cap, when an emergency application is made, the air coming from the brake pipe, through the quick action cap, will apply the locomotive brake.
145. Q. If the application cylinder pipe breaks, what effect will it have on the locomotive brake?
A. The locomotive brake cannot be applied with either automatic or independent brake valve. By plugging the pipe toward the distributing valve the automatic brake will be restored.
146. Q. If the distributing valve release pipe breaks, what will be the effect?
A. The holding feature of the brake will be lost; that is, the locomotive brake will release when the automatic brake valve is moved to either release or holding position, the same as with the old G-6 equipment.
147. Q. If the release pipe is broken and not plugged, can the independent brake be applied?
A. Yes, by placing the brake valve handle in quick-application position the brake will apply, but there will be a waste of air through the broken pipe, and the brake will release when the brake valve is returned to lap position.
148. Q. If the brake cylinder pipe breaks, can the locomotive brake be applied?
A. This depends on where the pipe breaks; if between the cut-out c.o.c.k and any one of the brake cylinders, close the cut-out c.o.c.k to that cylinder, and the other cylinders may be used. But if the pipe breaks at the distributing valve, the locomotive brake will be lost.
149. Q. If the brake pipe connection to the distributing valve breaks, what should be done?
A. Plug the end from the brake pipe; the locomotive brake must now be released by placing the independent valve in release position.
150. Q. If the brake pipe connection to the distributing valve breaks and is plugged, can the locomotive brake be operated?
A. The independent brake may be applied and released in the usual manner, but the automatic brake will be lost for service braking.
TYPE K TRIPLE VALVE