A. To apply the locomotive brake quickly, as in short switching.

115. Q. What brake cylinder pressure is usually developed with this brake?

A. About forty-five pounds.

DEAD ENGINE FEATURE

116. Q. What is the dead engine device?

A. The dead engine device is a pipe connection between the main reservoir and the brake pipe. In this pipe is found a combined strainer and check valve with a choke fitting and cut-out c.o.c.k, which when open forms a connection between the brake pipe and the main reservoir.

117. Q. What is the purpose of this device?

A. To provide a means of charging the main reservoir of an engine whose compressor is inoperative.

118. Q. What is the object of charging a main reservoir of an engine with a disabled compressor?

A. As the air used in the locomotive brake cylinders comes from the main reservoir, for the brakes to be operated on this engine it is necessary that its main reservoir be charged.

119. Q. With a 70-pound brake pipe pressure, what pressure should be had in the main reservoir when using this device?

A. About fifty pounds.

120. Q. When the dead engine feature is being used, in what position should the automatic and independent brake valves be carried?

A. Running position.

121. Q. What should be the position of the brake pipe cut-out c.o.c.k below the brake valve?

A. It should be closed.

DISTRIBUTING VALVE

122. Q. What is the duty of the distributing valve?

A. To admit air from the main reservoir to the locomotive brake cylinders when applying the brake, 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.

123. Q. To what is the distributing valve attached?

A. To the distributing valve reservoir.

124. Q. How many chambers has the distributing valve reservoir?

A. Two; pressure chamber and application chamber.

[Ill.u.s.tration: Fig. 8. Release, Automatic or Independent.

Connections: MR, Main Reservoir Pipe; IV, Distributing Valve Release Pipe; II, Application Cylinder Pipe; CYLS, Brake Cylinder Pipe; BP, Brake Pipe.]

125. Q. Name the different pipe connections to the distributing valve reservoir.

A. Referring to Fig. 8, the connection marked "MR" is the main reservoir supply pipe; "II", application cylinder pipe; "IV", distributing valve release pipe; "BP", brake pipe; "CYLS", brake cylinder pipe.

126. Q. To what do these different pipes connect?

A. The main reservoir supply pipe connects the distributing valve with the main reservoir pipe. The application cylinder pipe connects the application cylinder of the distributing valve with the independent and automatic brake valves. The distributing valve release pipe connects the application cylinder exhaust port in the distributing valve with the independent brake valve, and through it, when in running position, to the automatic brake valve. The brake cylinder pipe connects the distributing valve with the different brake cylinders on the locomotive.

The brake pipe branch pipe connects the distributing valve with the brake pipe.

127. Q. Explain the operation of the distributing valve when making an automatic service application of the brake.

A. When the brakes are fully charged, the brake pipe and pressure chamber pressures are equal, and when a gradual reduction of brake pipe pressure is made it will be felt in chamber "p" at the right of the equalizing piston 26, creating a difference in pressure on the two sides of the piston, causing it to move to the right. The first movement of the piston closes the feed groove "v", also moves the graduating valve 28, uncovering the service port "z" in the equalizing slide valve 31; this movement of the piston also causes the shoulder on the end of its stem to engage the equalizing slide valve, and the continued movement of the piston moves the valve to service position, in which port "z"

connects with port "h" in the seat of the valve, as shown in Fig. 9. As the equalizing slide valve chamber is at all times connected to the pressure chamber, air can now flow from this chamber to both the application cylinder and chamber through ports "z" and "h", cavity "n"

and port "w" until the pressure on the left or pressure chamber side of the equalizing piston 26 becomes slightly less than that in the brake pipe, when the piston and graduating valve will move to the left until the shoulder on the piston stem strikes the slide valve; this movement of the graduating valve closes the service port "z", thus closing the communication between the pressure chamber and application chamber and cylinder, also closing port "l" which leads to the safety valve. The distributing valve is now said to be in service lap position. (See Fig.

10.)

128. Q. Upon what does the pressure in the application chamber and cylinder depend when making a service application of the brake?

A. On the amount of brake pipe reduction; and as the relative volume of the pressure chamber and application cylinder and chamber is practically the same as that of an auxiliary reservoir and brake cylinder, it will be understood that one pound from the pressure chamber will make two and one-half pounds in the application chamber and cylinder; in other words, with the pressure chamber charged to seventy pounds and no pressure in the application chamber and cylinder, if they were connected and the pressure allowed to equalize it would do so at about fifty pounds; that is, twenty pounds from the pressure chamber will make fifty pounds in the application chamber and cylinder.

[Ill.u.s.tration: Fig. 9. Automatic Service.]

129. Q. How is the application piston 10 affected by the air pressure in the application cylinder "g"?

A. Pressure forming in this cylinder will force the piston to the right; the piston in moving will carry with it the exhaust valve 16, closing the exhaust ports "e" and "d", at the same time moving the application valve 5, opening the supply port "b", allowing main reservoir air from chamber "a" to flow through ports "b" and "C" to the connection marked "CYLS", and on to the different brake cylinders of the locomotive until the pressure in the brake cylinders and at the right of the application piston becomes slightly greater than that in chamber "g" when the application piston and valve will move back to lap position as shown in Figures 9 and 10.

130. Q. With the application valve in lap position, if there be brake cylinder leakage, will the locomotive brake leak off?

A. No; any drop in brake cylinder pressure will be felt in chamber "b"

at the right of the application piston 10, causing a difference in pressure on the two sides of the piston, thus allowing the pressure in the application cylinder to move the application piston and valve to the right, again opening the supply port "b" allowing a further flow of main reservoir air from chamber "a" to the brake cylinders until the pressure is again slightly greater than that in the application cylinder "g", when the application piston and valve will move back to lap position.

Thus in this way air will be supplied to the brake cylinders of the locomotive, holding the brake applied regardless of leakage.

131. Q. What effect will piston travel have on the pressure developed in the brake cylinders?

A. None; as the pressure in the brake cylinders is entirely dependent on the pressure in the application cylinder, which is not affected by piston travel.

132. Q. Explain the movement of the parts in the distributing valve when the automatic brake valve is moved to release position, after 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 a rise of pressure which is felt in chamber "p" on the right or brake pipe side of the equalizing piston 26; this increase of pressure will cause the piston to move toward the left, carrying the graduating valve 28 and slide valve 31 to release position.

[Ill.u.s.tration: Fig. 10. Service Lap.]

This allows the air from the application chamber and cylinder to flow to the distributing valve release pipe "IV" and on through the independent brake valve to the automatic brake valve, where the port to which this pipe leads is blanked by the automatic rotary valve, thus preventing the air from leaving the application chamber and cylinder, holding the locomotive brake applied while the train brakes are being released. The movement of the parts, and the results obtained are the same where the release is made in holding position.