96. Q. What is the purpose of the equalizing reservoir?

A. The purpose of the equalizing reservoir is to furnish a larger volume of air above the equalizing piston than is found in chamber "D", thus to enable the engineer to make a graduated reduction of the pressure above the equalizing piston.

97. Q. What defect will cause the brake pipe and main reservoir pressure to equalize when the handle is in running position?

A. This may be caused by leakage past the rotary valve, defective body gasket, or leakage by the feed valve or its case gasket. To determine which part is at fault, close the cut-out c.o.c.k under the brake valve and move the handle to service position, exhausting all air from chamber "D" and the brake pipe; return the handle to lap position. Leakage of air past the rotary valve is generally into the brake pipe port which allows the air to come in under the equalizing piston, thus forcing it upward, unseating the brake pipe exhaust valve, allowing this air to escape to the atmosphere at the brake pipe exhaust port. Leakage past the body gasket allows air to enter chamber "D", above the equalizing piston, holding it in its lower position, keeping the brake pipe exhaust port closed, thereby preventing the escape of this air to the atmosphere. Since the capacity of the equalizing reservoir and chamber "D" is small, such a leak will cause the black hand to quickly move up to the position of the red hand. To determine if the leakage be in the feed valve or its gasket, recharge the brake pipe to some pressure below the adjustment of the feed valve, then place the handle in lap position.

If the black hand on the air gauge remains stationary, it is fair to a.s.sume that the trouble is in the feed valve or its gasket, as in this position of the brake valve the feed valve is cut out.

98. Q. With the engine alone, the brake pipe pressure will equalize with that in the main reservoir, while when coupled to a train the pressure will remain at that for which the feed valve is adjusted; where is the trouble?

A. This is caused by light leakage of main reservoir air into the brake pipe, and may come past the rotary valve, body gasket, or feed valve, and with the lone engine is sufficient to raise the brake pipe pressure to that in the main reservoir; while, when coupled to a train, the brake pipe leakage of which is greater than this amount, this leakage will not be noticed.

THE FEED VALVE AND ITS DEFECTS

99. Q. What do Figures 6 and 7 represent?

A. These are diagrams of the B-6 feed valve in both open and closed positions.

100. Q. Name the different parts of the feed valve.

A. The valve consists of the following parts: 2, valve body; 3, pipe bracket; 5, cap nut; 6, piston spring; 7, piston spring tip; 8, supply valve piston; 9, supply valve; 10, supply valve spring; 11, regulating valve cap nut; 12, regulating valve; 13, regulating valve spring; 14, diaphragm; 15, diaphragm ring; 16, diaphragm spindle; 17, regulating spring; 18, spring box; 19 and 20, stop rings; 21, clamping screw; 22, hand wheel.

101. Q. Explain the operation of the feed valve.

A. The feed valve consists of two portions, the supply and regulating portions. The supply portion consists of a slide valve 9 and a piston 8 (see Fig. 6). The supply valve 9 opens and closes communication between the main reservoir and the feed valve pipe and is moved by the piston 8 which is operated by main reservoir air entering through pa.s.sage "a" on one side or by the pressure of the spring 6 on the other side. The regulating portion consists of a bra.s.s diaphragm 14, on one side of which is the diaphragm spindle 16, held against the diaphragm by the regulating spring 17, and on the other side a regulating valve 12, held against the diaphragm or its seat, as the case may be, by the spring 13.

Chamber "L" at the left of the diaphragm is open to the feed valve pipe through the pa.s.sage "e" and "d". The feed valve is adjusted by turning the hand wheel 22 in or out, thus increasing or decreasing the pressure exerted by the spring on the diaphragm. The same results are obtained in turning the hand wheel 22 as when turning the adjusting screw in the older types of feed valves.

[Ill.u.s.tration: Fig. 6. Diagram of B-6 Feed Valve, Closed.

Connections: MR, Main Reservoir Pipe; FVP, Feed Valve Pipe.]

Air from the main reservoir flowing through pa.s.sage "a" into chamber "B"

will force the piston 8 to the left against the tension of the spring 6; the piston in moving will take with it the supply valve 9, opening the supply port in the valve to port "c" in its seat as shown in Fig. 7.

Main reservoir air will now be free to flow through pa.s.sage "a", chamber "B", port "c" and pa.s.sage "d" to the feed valve pipe. Air coming through port "c" also flows through pa.s.sage "e" to chamber "L" at the left of the diaphragm 14, and this pressure tends toward forcing the diaphragm to the right; but the diaphragm being supported by the regulating spring 17, will remain in its position at the left, holding the regulating valve 12 off its seat, until the pressure in chamber "L" exceeds the tension of the regulating spring 17. Air, therefore, continues to flow from the main reservoir through a, B, c, d and e to the feed valve pipe and chamber "L", increasing the pressure, until the pressure on the diaphragm 14 overcomes the tension of the regulating spring 17, when the diaphragm will move to the right, allowing the spring 13 to force the regulating valve 12 to its seat, closing port "K". Chambers "G" and "H"

are then no longer open to chamber "L" and the feed valve pipe, and these chambers being small, the pressure raises quickly to main reservoir pressure due to the leakage of air past the supply piston 8, which forms but a loose fit in its bushing. When the pressure in chamber "G" becomes nearly equal to that in chamber "B", the piston spring "6"

forces the piston 8 and its slide valve 9 to closed position, which prevents further flow of air from the main reservoir to the feed valve pipe (see Fig. 6). The feed valve will remain in closed position until the pressure in chamber "L" is slightly reduced so that the pressure on the diaphragm 14 is no longer able to withstand the pressure of the regulating spring 17, which then forces the diaphragm to the left, lifting the regulating valve 12 from its seat and again opening port "K"

to chamber "L", thus dropping the pressure at the left of piston 8 below that of the main reservoir acting on the opposite side of the piston.

[Ill.u.s.tration: Fig. 7. Diagram of B-6 Feed Valve, Open.]

Main reservoir pressure then forces the supply piston and valve over into open position, as shown in Fig. 7, and allows a further flow of air through port "c" to the feed valve pipe to again raise its pressure to the adjustment of the feed valve, when the valve will again close.

102. Q. What is the duty of the feed valve?

A. To control and maintain a constant pressure in the brake pipe when the brake valve is in running or holding position.

103. Q. What defect in the feed valve will cause the brake pipe pressure to equalize with that in the main reservoir?

A. This may be caused by a defective feed valve case gasket, permitting main reservoir air to leak into the feed valve pipe, or leakage past the supply valve, or the regulating valve held from its seat, or the supply valve piston too tight a fit in its cylinder.

104. Q. If the brake pipe charges too slowly when nearing the maximum pressure, where is the trouble?

A. This may be caused by a loose-fitting supply valve piston 8, or the port past the regulating valve 12 partly stopped up.

105. Q. How should the feed valve be tested?

A. With the brakes released, and charged to the adjustment of the feed valve, create a brake pipe leak of from seven to ten pounds and note the black hand on the brake pipe gauge. The fluctuation of this hand will indicate the opening and closing of the feed valve, which should not permit a variation of over two pounds in brake pipe pressure; if it does, it indicates a dirty condition of the valve, and should be cleaned.

106. Q. If the main reservoir pipe connection to the feed valve breaks, what should be done?

A. This will cause a loss of main reservoir air, and both ends of the pipe must be plugged. As no air now comes to the feed valve to charge the brake pipe in running or holding position of the brake valve, the handle must be carried in release position.

107. Q. What must be done if the pipe between the feed valve and automatic brake valve breaks?

A. Slack off on the regulating nut of the feed valve until all tension is removed from the regulating spring and plug the pipe toward the brake valve. To charge the brake pipe, the brake valve handle must be carried in release position.

108. Q. If the feed valve becomes defective so that it will not control brake pipe pressure, what may be done?

A. As the reducing valve used for the independent brake, and the feed valve are practically the same, they may be changed one for the other, the reducing valve taking the place of the feed valve.

INDEPENDENT BRAKE VALVE

109. Q. Name the different positions of the independent brake valve used with the E-T equipment.

A. Release, running, lap, slow-application position, quick-application position.

110. Q. What is the purpose of release position?

A. To release the locomotive brake when the automatic brake valve is in other than running position.

111. Q. What is the purpose of running position?

A. This is the proper position for the brake valve when not in use, and to release the locomotive brake when the automatic brake valve is in running position.

112. Q. What is the purpose of lap position?

A. To hold the locomotive brake applied after an independent application.

113. Q. What is the purpose of slow-application position?

A. This position may be used when it is desired to make a light or gradual application of the brake, as in stretching or bunching the slack of a train.

114. Q. What is the purpose of quick-application position?