slide valve
chamber. Brake pipe air will now be free to flow past the piston to the
slide valve chamber and out at "R" to the auxiliary reservoir. Air will
continue to feed through the groove "i" until the auxiliary reservoir
and brake pipe pressures are equal, and it is then we say that the brake
is fully charged. Brake pipe air entering chamber "a" will lift the
check valve 15, and charge chamber "Y" to brake pipe pressure. When a
gradual reduction of brake pipe pressure is made, as in a service
application of the brakes, the pressure being reduced in chamber "h",
auxiliary reservoir pressure will move the piston 4 toward service
position. (See Fig. 14.) The first movement of the piston closes the
feed groove "i", thus closing communication between the auxiliary
reservoir and the brake pipe, preventing a back-flow of air from the
auxiliary to the brake pipe, and at the same time moving the graduating
valve 7, opening the service port "Z" in the slide valve. The continued
movement of the piston will move the slide valve until the service port
"Z" registers with the brake cylinder port "r" in the valve seat, thus
creating a communication between the auxiliary reservoir and the brake
cylinder. Air will now flow from the auxiliary to the brake cylinder
until the pressure on the auxiliary side of the piston 4 becomes
slightly less than in the brake pipe, when the piston and the graduating
valve 7 will move back just far enough to close the service port "Z",
thus closing communication between the auxiliary reservoir and the
brake cylinder. At the same time, the first movement of the graduating
valve connects the two ports "o" and "q" in the slide valve through the
cavity "v" in the graduating valve, and the movement of the slide valve
brings port "o" to register with port "y" in the slide valve seat, and
port "q" with port "t". This permits the air in chamber "Y" to flow
through port "y", "o", "v", "q", and "t", thence around the emergency
piston 8, which fits loosely in its cylinder, to chamber "X" and the
brake cylinder. When the pressure in chamber "Y" has reduced below the
brake pipe pressure remaining in chamber "a", the check valve 15 is
raised and allows brake pipe air to flow past the check valve and
through the ports above mentioned to the brake cylinder.

[Illustration: Fig. 14. Quick Service Position.]

The size of these ports are so proportioned that the flow of air from
the brake pipe to the top of the emergen