Part 13

A. Air will continue to flow to the brake cylinder until the pressure on the auxiliary side of the triple piston becomes slightly less than that on the brake pipe side, when the piston 4 and the graduating valve 7 will move to the left until the shoulder on the piston stem strikes the slide valve. (See Fig. 16.) This movement has caused the graduating valve to close the service port "Z", thus cutting off any further flow of air from the auxiliary to the brake cylinder and also port "o", thus preventing any further flow of air from the brake pipe to the brake cylinder. The triple valve is now said to be in lap position.

155. Q. How is the triple valve affected by a further reduction of brake pipe pressure?

A. A further reduction of brake pipe pressure will cause the triple piston 4 and the graduating valve 7 to again move to the right, opening ports "Z" and "o", allowing a further flow of brake pipe and auxiliary air to the brake cylinder. This may be continued until the auxiliary reservoir and brake cylinder pressures become equal, after which any further reduction of brake pipe pressure is only a waste of air. With seventy pounds brake pipe pressure, and eight-inch piston travel, a twenty-pound reduction will cause equalization at about fifty pounds.

156. Q. Explain the operation of the triple valve in the release of the brake.

A. To release the brakes and recharge the auxiliary reservoirs, air is admitted through the brake valve to the brake pipe. This increase of pressure on the brake pipe side of the triple valve piston 4 above that on the other side causes the piston and slide valve to move back to release position, which permits the air in the brake cylinder to flow to the atmosphere, through the exhaust port of the triple, thus releasing the brake. At the same time, air from the brake pipe flows through the feed groove "i" around the triple piston to the auxiliary reservoir, which is thus recharged. Now the "K" triple valve has two release positions: =Full Release= and =Retarded Release=. To which of these two positions the parts will move when the brakes are released, depends upon how the brake pipe pressure is increased. It is generally understood that those cars toward the head end of the train, receiving the air first, will have their brake pipe pressure raised more rapidly than those in the rear; thus the friction of the brake pipe causes the pressure to build up more rapidly in the chamber "h" of the triple valve toward the front end of the train than in those in the rear. As soon as the pressure is enough greater than the auxiliary reservoir pressure to overcome the friction of the piston, graduating valve and slide valve, all three are moved toward the left until the piston stem strikes the retarding stem 31, which is held in position by the retarding spring 33. Where the rate of increase of brake pipe pressure is slow, it will be impossible to raise the pressure in chamber "h" sufficiently to overcome the tension of the retarding spring 33, and the triple valve will remain in full release position, as shown in Fig. 13. Brake cylinder air will now be free to exhaust through port "r", large cavity "n" in the slide valve and port "p" leading to the atmosphere. If, however, the triple valve is near the head end of the train, and the brake pipe pressure builds up more rapidly than the auxiliary can recharge, an excess of pressure will be obtained in chamber "h" over that in the auxiliary reservoir, and will cause the piston 4 to compress the retarding spring 33, and move the triple valve parts to retarded release position as shown in Fig. 17.

157. Q. What effect has retarded release position of the triple valve on the release of the brakes?

A. In this position of the triple valve, cavity "n" in the slide valve connects port "r" leading to the brake cylinder, with port "p" to the atmosphere, and the brake will release; but as the small "tail port" extension of cavity "n" is over exhaust port "p", the discharge of air from the brake cylinder is quite slow.

158. Q. What is the object of delaying the exhaust of the brake cylinder air?

A. In this way, the brakes on the front end of the train require a longer time to release than those on the rear. This feature is called =retarded release=, and although the triple valves near the locomotive commence to release before those in the rear, yet the exhaust of air from the brake cylinder is sufficiently slow to hold back the release of the brakes at the front end of the train long enough to insure a uniform release of the brakes on the train as a whole. This permits of releasing the brakes on very long trains at low speeds without danger of damaging train.

159. Q. What other desirable feature is found in this position of the triple valve?

A. In this position, the back of the piston is in contact with the end of the slide valve bush, and, as these two surfaces are ground to an accurate fit, the piston makes a tight "seal" on the end of the bush except at one point, where a feed groove is cut in the piston to allow air to pass around the end of the slide valve bush into chamber "R" and the auxiliary reservoir. This feed groove is much smaller than the feed groove "i" in the piston bush, so that when the triple valve piston is in =Retarded Release= position the recharge of the auxiliary reservoir takes place much more slowly than when it is in =Full Release= position, thus permitting a greater volume and pressure of air to flow toward the rear of the train.

160. Q. Explain the operation of the triple valve in emergency position.

A. When any sudden reduction of brake pipe pressure is made below that in the auxiliary reservoir, it will be felt in chamber "h" in front of piston 4 and cause this piston to move to the extreme right, as shown in Fig. 18. This movement of the parts will open port "t" in the slide valve seat and allow air from the auxiliary reservoir to flow to the top of the emergency piston 8, forcing the latter downward and opening emergency valve 10. The unseating of the emergency valve allows the air in chamber "Y" to escape to the brake cylinder, thus permitting brake pipe pressure in chamber "a" to lift the check valve 15 and flow to the brake cylinder through chambers "Y" and "X", until brake cylinder and brake pipe pressure nearly equalize, when the check valve is forced to its seat by the check valve spring 12, preventing the air in the cylinder from escaping back into the brake pipe again. The emergency valve and piston will now return to their normal position. At the same time port "s" in the slide valve registers with port "r" in the slide valve seat, and allows air from the auxiliary reservoir to flow to the brake cylinder. This sudden discharge of brake pipe air into the brake cylinder has the effect on the next triple valve, which in turn vents brake pipe air that affects the following triple valve and so on throughout the train.

NEW YORK AIR BRAKE

AIR COMPRESSOR

161. Q. What do Figures 19 and 20 represent?

A. These are cross-sectional views of the New York compressor.

162. Q. Of what does the valve gear of this compressor consist?

A. Of two main valves, actuated by tappet rods which enter into the hollow piston rods, and are moved by tappet plates, which are fastened to the steam piston heads.

163. Q. How is the admission and exhaust of steam controlled?

A. The valve under the cylinder at the right controls the flow of steam to and from the cylinder at the left; while the valve under the cylinder at the left controls the flow of steam to and from the cylinder at the right.

164. Q. Explain the operation of the steam end of the compressor.

A. Assuming both pistons are at the bottom of their cylinders, when the compressor throttle is opened, live steam will flow to both steam chests "B" (see Fig. 19), and through port "o" to the under side of the piston "T" and through port "g" to the upper side of piston "H". The steam under piston "T" will force it upward, and when it very nearly completes its stroke, the tappet plate "Q" will engage the button on the end of the tappet rod "P", moving the main valve "C" to its upper position. In this position the exhaust cavity "r" in the main valve connects port "g" with the exhaust port "X", thus allowing steam above the piston "H" to escape to the exhaust, at the same time steam is admitted through port "s" to the under side of piston "H", forcing it upward. As this piston very nearly completes its stroke, the tappet plate "L" (see Fig. 20) engages the button on the tappet rod "P", moving the main valve "A" to its upper position. Exhaust cavity "r" now connects port "o", which leads to the lower end of the cylinder at the right, with the exhaust port "X", thus allowing the steam under piston "T" to escape to the exhaust, at the same time steam is admitted through port "V" to the upper end of the cylinder at the right, on top of piston "T", forcing it downward; as it very nearly completes its stroke, the tappet plate "Q" engages the shoulder on the tappet rod "P", moving the main valve "C" to its lower position. The exhaust cavity "r" in the valve now connects port "s" with the exhaust port "X", allowing steam below piston "H" to escape to the exhaust, and at the same time steam is admitted to the top of this piston, forcing it down, thus completing a cycle of the compressor.

165. Q. Explain the operation of the air end of the compressor.

A. As the piston in the low pressure cylinder "D" moves up (see Fig. 19), a partial vacuum is formed below it, and air flowing through the strainer passes downward through the air passage, then past the lower receiving valve "W" into the lower end of the cylinder, filling it with air at about atmospheric pressure. In the meantime the air that is being compressed above the piston holds the receiving valve "U" to its seat, and lifts the upper intermediate discharge valve "K" from its seat, allowing the air to pass from the low to the high pressure cylinder "F". The high pressure piston now moving up causes a partial vacuum to be formed below it, and air from the atmosphere flows past the lower receiving valve "N", filling this end of the cylinder with air at about atmospheric pressure. The air above the piston being compressed, holds the upper intermediate valve "K" and receiving valve "J" to their seats and lifts the upper final discharge valve "M", allowing the air to pass to the main reservoir. The action is the same on the down stroke, only air is compressed in the opposite end of the cylinders and the opposite air valves are used.

166. Q. What should be the lift of the different air valves?

A. In the No. 1 and No. 2 compressors all valves should have 1/16-inch lift; in the No. 5 and No. 6 all valves should have 3/16-inch lift.

167. Q. If a receiving valve to the low pressure air cylinder breaks or sticks open, what effect will it have on the compressor, and how may it be located?

A. No air will be compressed in the low pressure cylinder, as the piston moves toward the defective valve, and may be located by noting the movement of the low pressure piston, as it will be much quicker toward the defective valve than the opposite stroke. Air will blow back to the atmosphere as the piston moves toward the defective valve, and may be detected by holding the hand over the strainer.

168. Q. If an intermediate discharge valve breaks or sticks open, what effect will it have on the compressor, and how may it be located?

A. If an intermediate discharge valve breaks or sticks open, no air will be compressed by that end of the compressor where is located the defective valve, as the air will simply flow back and forth from the high to the low pressure cylinders; no air will be taken in from the atmosphere through the strainer as the pistons move from the defective valve.

169. Q. If a final discharge valve breaks, what effect will it have on the compressor?

A. Main reservoir air will be free to return to the high pressure cylinder as the high pressure piston moves from the defective valve; therefore, no air will be taken in through the receiving valve of the high pressure air cylinder at the end where is located the defective valve. The low pressure piston will make a slow stroke toward the defective valve and a normal stroke from it; while the high pressure piston will make a slow stroke toward the defective valve and a quick stroke from it. Defective air valves may generally be located by noting the temperature of the valve chamber in which they are located.

170. Q. What will cause the compressor to run hot?

A. Running the compressor too fast; working against high pressure; air piston packing rings leaking; air cylinder worn; air passages or discharge pipe partially stopped up; air valves leaking; air valves stuck shut; or lack of lubrication.

171. Q. How should the air end of the compressor be oiled, and what grade of oil used?

A. Oil should be used sparingly in the low pressure cylinder, but more is required in the high pressure cylinder, owing to higher temperature. A good quality of valve oil should be used.

172. Q. How is the steam end of the compressor affected by the use of too much oil?

A. This may cause the compressor to short stroke, and where the piston type of valve is used, may cause the compressor to stop.

L-T EQUIPMENT

AUTOMATIC CONTROL VALVE

173. Q. What is the duty of the control valve?

A. To admit air from the main reservoir to the locomotive brake cylinders when applying the brakes; to automatically maintain the brake cylinder pressure against leakage; to develop the proper brake cylinder pressure regardless of piston travel; and to exhaust the air from the brake cylinders when releasing the brake, in all automatic applications of the brake.

174. Q. Explain the operation of the control valve when making an automatic service application of the brake.

A. Air enters the control valve at the connection marked "BP" (Fig. 21), which leads to chamber "F" above the piston 3, forcing it down, uncovering the feed groove "G" in the bushing, allowing air to feed past the piston into the slide valve chamber, and then through port "H" to the auxiliary reservoir. The air will feed through in this manner until the auxiliary reservoir and brake pipe pressure equalize. When a gradual reduction of brake pipe pressure is made, it will be felt in chamber "F", above piston 3, creating a difference in pressure on the two sides of the piston, which will cause it to move upward.

The first movement of the piston closes the feed groove "G", also moves the graduating valve 10, uncovering the service port "J" in the slide valve 4, and the continued movement of the piston moves the slide valve to service position, in which the service port "J" connects with port "E" in the valve seat. (See Fig. 22.) As the slide valve chamber and auxiliary reservoir are connected at all times, air can now flow from the auxiliary to the control cylinder "D" and control reservoir, through ports "H", "J" and "E", until the pressure on the lower or auxiliary side of piston 3 becomes slightly less than that in chamber "F" or brake pipe side, when the piston and graduating valve will move down until the shoulder on the piston strikes the slide valve; this movement of the graduating valve closes the service port "J", thus closing the communication between the auxiliary and control cylinder and reservoir, also closing port "W", which leads to the safety valve. (See Fig. 23.)

175. Q. How is piston 2 affected by the air pressure in the control cylinder "D"?

A. Pressure forming in this cylinder will force the piston downward. The piston in moving down will carry the exhaust valve 7 with it, closing the exhaust port "N" and moves the preliminary admission valve "1A" from its seat against the tension of spring 8, allowing the pressure in chamber "O" to pass to the brake cylinders, thus creating a balancing effect on valve 1, which allows it to be opened against main reservoir pressure, thus allowing main reservoir air to flow from chamber "A" to chamber "B" and the brake cylinders on the locomotive (see Fig. 22) until the pressure in the brake cylinders and chamber "B", below piston 2, becomes slightly greater than that in the control cylinder "D" when the piston will move up just far enough to allow the valves "1" and "1A" to be seated, or to lap position. (See Fig. 23.)

176. Q. With the control valve now in lap position, will the brake release on account of brake cylinder leakage?

A. Any drop in brake cylinder pressure will be felt in chamber "B" below the piston 2, causing a difference in pressure on the two sides of the piston, allowing the pressure in the control cylinder "D" to move the piston 2 down, unseating the admission valves, allowing a further flow of main reservoir air from chamber "A" to chamber "B" and the brake cylinders until the pressure is again slightly greater than that in the control cylinder "D", when the piston 2 will again move up, allowing the admission valves to close. Thus in this way air will be supplied to the brake cylinders of the locomotive, holding the brakes applied regardless of leakage.

177. Q. Explain the movement of the parts in the control valve, when the automatic brake valve is moved to release position, following an automatic application of the brake.

A. In release position of the brake valve, air from the main reservoir flows direct to the brake pipe, causing an increase of pressure, which is felt in chamber "F" on the upper side of piston 3; this increase of pressure will cause the piston to move down, carrying with it the graduating valve 10 and slide valve 4 to release position. This allows air from the control cylinder "D" and control reservoir to flow through the release pipe "IV" and on to the automatic brake valve, where the port to which this pipe leads is blanked by the automatic rotary valve, which prevents the air leaving the control cylinder and reservoir, thus holding the locomotive brake applied while the train brakes are being released. The movement of the parts are the same where the release is made in holding position.

178. Q. Explain the movements of the parts in the control valve when the automatic brake valve is moved to running position, after having first been moved to release or holding position.

A. In this position of the brake valve the port to which the release pipe "IV" is connected is open to the exhaust, thus allowing the air in the control cylinder and reservoir to escape to the atmosphere. The reduction of pressure in the control cylinder "D" below that in chamber "B" causes the control piston 2 to move up, carrying with it the exhaust valve 7 to release position, opening the exhaust port "N", thus allowing the air to return from the brake cylinders through ports "C" and "N" to the atmosphere, releasing the brake. (See Fig. 21.)

179. Q. Explain what takes place in the control valve when an automatic emergency application of the brake is made.

A. Any sudden reduction of brake pipe pressure will be felt on the brake pipe side of piston 3, and will cause it and the valve 4 to move to their extreme upper position, the knob on the piston striking the graduating stem 13, causing it to compress the spring 14, moving the emergency valve 15 upward, opening port "Q"; this allows brake pipe air to flow against valve 16, unseating it, then through port "T" to the brake cylinder. (See Fig. 24.) In the meantime auxiliary reservoir air can flow past the end of the slide valve through port "E" to the control cylinder "D" and control reservoir, forcing piston 2 downward unseating valves "I" and "IA", thus allowing main reservoir air to flow to the brake cylinders, applying the brake.

180. Q. At what pressure will the auxiliary reservoir and control reservoir equalize when using seventy pounds brake pipe pressure?

A. At about fifty pounds; however, with the automatic brake valve in emergency position, there is a small port in the rotary valve (called the blow-down timing port) opened to the control reservoir pipe and control reservoir which allows main reservoir air to flow to the control reservoir and cylinder, raising the pressure to the adjustment of the safety valve.

181. Q. At what pressure is the safety valve adjusted?

A. At fifty pounds.

182. Q. What types of brake valve are used with this equipment?

A. The automatic brake valve is of the rotary valve type and is the same valve as used with the E-T equipment. The straight air brake valve is of the slide valve type. The control valve takes no part in the application or release of the straight air brake. What has been said of the H-6 brake valve used with the E-T equipment, applies to the automatic brake valve used with the L-T equipment.

BROKEN PIPES

183. Q. If the main reservoir supply pipe to the automatic control valve breaks, what should be done?

A. Plug the pipe toward the main reservoir. The locomotive brake cannot be applied in an automatic service application; but if the control valve be equipped with a quick action cap and an emergency application is made, the air vented from the brake pipe to the brake cylinder will apply the brake. The independent brake will not be affected.

184. Q. What will be the effect if the release pipe breaks?

A. The holding feature of the brake will be lost; that is, the brake will release when the automatic brake valve is returned to release or holding position.

185. Q. If the brake cylinder pipe breaks, can the locomotive brake be applied with the automatic brake valve? With the independent brake valve?

A. This depends on where the pipe breaks; if between the cut-out cock and any one of the brake cylinders, close the cut-out cock to that cylinder, and the other cylinders may be used. But if the pipe breaks between the control valve and the double-throw check valve, the automatic brake is lost; if the break be between the independent brake valve and double-throw check valve, the independent brake is lost.

186. Q. If the brake cylinder pipe breaks and is not plugged, what must be done?

A. Close the cut-out cock in the main reservoir supply pipe, this to avoid the waste of air when a brake application is made on the train.

187. Q. If the brake pipe connection to the control valve breaks, what should be done?

A. Plug the end leading from the brake pipe; the automatic brake cannot be applied on the locomotive, but the independent brake will not be affected.

188. Q. If the control cylinder pipe breaks, what effect will it have and what must be done?

A. The locomotive brake cannot be applied with the automatic brake valve; by plugging the pipe, this feature of the brake will be restored, but the independent release feature will be lost.

189. Q. If any of the pipes here enumerated breaks, will it in any way affect an application of the independent brake?

A. No; as the independent and automatic features are entirely separate from each other; that is, the automatic control valve is not brought into use when an independent application of the brake is made.

CONTROL VALVE DEFECTS

190. Q. If there is a blow at the control valve exhaust port when the brake is released, where would you look for the trouble?