inder 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.)

[Illustration: 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 pi