cy piston 8, is not sufficient
to force the latter downward and thus cause an emergency application,
but at the same time takes enough air from the brake pipe to cause a
local reduction of brake pipe pressure at that point, thus assisting the
brake valve in increasing the rapidity with which the brake pipe
reduction travels through the train. The triple valve is now said to be
in "Quick Service" position. (See Fig. 14.)

153. Q. Will the triple valve move to quick service position whenever a
gradual reduction brake pipe reduction is made?

A. No; with short trains, the brake pipe volume being comparatively
small, will reduce more rapidly for a certain reduction at the brake
valve than with a long train. Therefore, with a short train, the brake
pipe pressure reducing more quickly, the triple piston and its valves
will move to "full service" position, as shown in Fig. 15. In this
position the quick service port "y" is closed, so that no air flows from
the brake pipe to the brake cylinder. Thus, when the brake pipe
reduction is sufficiently rapid, there is no need for this quick service
reduction, and the triple valve automatically cuts out this feature of
the valve when not required.

154. Q. How long will the auxiliary reservoir air continue to flow to
the brake cylinder?

A. Air will continue to flow to the brake cylinder until the pressure on
the auxiliary side of the triple piston becomes slightly less than that
on the brake pipe side, when the piston 4 and the graduating valve 7
will move to the left until the shoulder on the piston stem strikes the
slide valve. (See Fig. 16.) This movement has caused the graduating
valve to close the service port "Z", thus cutting off any further flow
of air from the auxiliary to the brake cylinder and also port "o", thus
preventing any further flow of air from the brake pipe to the brake
cylinder. The triple valve is now said to be in lap position.

155. Q. How is the triple valve affected by a further reduction of brake
pipe pressure?

[Illustration: Fig. 15. Full Service Position.]

A. A further reduction of brake pipe pressure will cause the triple
piston 4 and the graduating valve 7 to again move to the right, opening
ports "Z" and "o", allowing a further flow of brake pipe and auxiliary
air to the brake cylinder. This may be continued until the auxiliary
reservoir and brake cylinder pressures become equal, after which any
further reduction of brake pipe pressure is onl