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.
[Illustration: 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.
[Illustration: 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.
133. Q. Explain the movement of the parts in the distributing valve when
the brake valve is moved to running position after having first been
moved to release or holding position, following a brake application.
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.