ing
33, and move the triple valve parts to retarded release position as
shown in Fig. 17.

157. Q. What effect has retarded release position of the triple valve on
the release of the brakes?

A. In this position of the triple valve, cavity "n" in the slide valve
connects port "r" leading to the brake cylinder, with port "p" to the
atmosphere, and the brake will release; but as the small "tail port"
extension of cavity "n" is over exhaust port "p", the discharge of air
from the brake cylinder is quite slow.

[Illustration: Fig. 17. Retarded Release and Charging Position.]

158. Q. What is the object of delaying the exhaust of the brake cylinder
air?

A. In this way, the brakes on the front end of the train require a
longer time to release than those on the rear. This feature is called
=retarded release=, and although the triple valves near the locomotive
commence to release before those in the rear, yet the exhaust of air
from the brake cylinder is sufficiently slow to hold back the release of
the brakes at the front end of the train long enough to insure a uniform
release of the brakes on the train as a whole. This permits of releasing
the brakes on very long trains at low speeds without danger of damaging
train.

[Illustration: Fig. 18. Emergency Position.]

159. Q. What other desirable feature is found in this position of the
triple valve?

A. In this position, the back of the piston is in contact with the end
of the slide valve bush, and, as these two surfaces are ground to an
accurate fit, the piston makes a tight "seal" on the end of the bush
except at one point, where a feed groove is cut in the piston to allow
air to pass around the end of the slide valve bush into chamber "R" and
the auxiliary reservoir. This feed groove is much smaller than the feed
groove "i" in the piston bush, so that when the triple valve piston is
in =Retarded Release= position the recharge of the auxiliary reservoir
takes place much more slowly than when it is in =Full Release= position,
thus permitting a greater volume and pressure of air to flow toward the
rear of the train.

160. Q. Explain the operation of the triple valve in emergency position.

A. When any sudden reduction of brake pipe pressure is made below that
in the auxiliary reservoir, it will be felt in chamber "h" in front of
piston 4 and cause this piston to move to the extreme right, as shown in
Fig. 18. This movement of the parts will open port "t" in the sli