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 pa.s.sages 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?

[Ill.u.s.tration: Fig. 20. High Pressureiston Moving Upward. Low Pressure Piston at Rest.]

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.

[Ill.u.s.tration: Fig. 21. Automatic Control Valve. Full Release.]

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 pa.s.s 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.)

[Ill.u.s.tration: Automatic Control Valve. Service Position. Fig. 22.]

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.

[Ill.u.s.tration: Automatic Control Valve. Service Lap Position. Fig. 23.]

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 k.n.o.b 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.

[Ill.u.s.tration: Fig. 24. Automatic Control Valve. Emergency Position.

(With Quick Action Cylinder Cap.)]

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 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 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?