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 assist 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.