[Illustration: Fig. 13. Full Release and Charging Position.]
A. When air is admitted to the brake pipe it is free to enter the triple
at "a" (see Fig. 13) and flow through the passage "e" to chamber "f",
thence through port "g" to chamber "h" in front of the triple valve
piston 4. Pressure forming in chamber "h" will force the piston to the
left until its packing ring uncovers the feed groove "i" in the bushing,
thus creating a communication between chamber "h" and the 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 emergency 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 only a waste of air. With
seventy pounds brake pipe pressure, and eight-inch piston travel, a
twenty-pound reduction will cause equalization at about fifty pounds.
[Illustration: Fig. 16. Lap Position.]
156. Q. Explain the operation of the triple valve in the release of the
brake.
A. To release the brakes and recharge the auxiliary reservoirs, air is
admitted through the brake valve to the brake pipe. This increase of
pressure on the brake pipe side of the triple valve piston 4 above that
on the other side causes the piston and slide valve to move back to
release position, which permits the air in the brake cylinder to flow to
the atmosphere, through the exhaust port of the triple, thus releasing
the brake. At the same time, air from the brake pipe flows through the
feed groove "i" around the triple piston to the auxiliary reservoir,
which is thus recharged. Now the "K" triple valve has two release
positions: =Full Release= and =Retarded Release=. To which of these two
positions the parts will move when the brakes are released, depends upon
how the brake pipe pressure is increased. It is generally understood
that those cars toward the head end of the train, receiving the air
first, will have their brake pipe pressure raised more rapidly than
those in the rear; thus the friction of the brake pipe causes the
pressure to build up more rapidly in the chamber "h" of the triple valve
toward the front end of the train than in those in the rear. As soon as
the pressure is enough greater than the auxiliary reservoir pressure to
overcome the friction of the piston, graduating valve and slide valve,
all three are moved toward the left until the piston stem strikes the
retarding stem 31, which is held in position by the retarding spring 33.
Where the rate of increase of brake pipe pressure is slow, it will be
impossible to raise the pressure in chamber "h" sufficiently to overcome
the tension of the retarding spring 33, and the triple valve will remain
in full release position, as shown in Fig. 13. Brake cylinder air will
now be free to exhaust through port "r", large cavity "n" in the slide
valve and port "p" leading to the atmosphere. If, however, the triple
valve is near the head end of the train, and the brake pipe pressure
builds up more rapidly than the auxiliary can recharge, an excess of
pressure will be obtained in chamber "h" over that in the auxiliary
reservoir, and will cause the piston 4 to compress the retarding spring
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.