Below we illustrate the main parts of the Westinghouse brake as applied
to a vehicle. The supplementary reservoir brake cylinder and triple
valve are shown in position, and as fitted upon the engine, tender, and
each vehicle of the train. Air compressed by a pump on the locomotive
to, say, 70 lb. or 80 lb. to the square inch fills the main reservoir on
the engine, and flowing through the driver's brake valve and main pipe,
also charges the supplementary reservoirs throughout the train. When
a train is running, uniform air pressure exists throughout its
length--that is to say, the main reservoir on the engine, the pipe from
end to end of train, the triple valves and supplementary reservoirs on
each vehicle, are all charged ready for work, the brake cylinders being
empty and the brakes off. The essential principle of the system is,
that maintaining the pressure keeps the brakes off, but letting the air
escape from the brake pipe, purposely or accidentally, instantly applies
them. It follows, therefore, that the brake may be applied by the driver
or any of the guards, or if necessary by a passenger, by the separation
of a coupling, or the failure or injury to a vital part of the
apparatus, whether due to an accident to the train or to the brake; and
as the brake on each vehicle is complete in itself and independent,
should the apparatus on any one carriage be torn off, the brake will
nevertheless remain applied for almost any length of time upon the rest
of the train.
The triple valve, as will be seen, is simply a small piston, carrying
with it a slide valve, which can be moved up or down by increasing or
decreasing the pressure in the brake pipe. As soon as the air from the
main reservoir is turned into the brake pipe, by means of the driver's
valve, the piston is pushed up into the position shown, and air is
allowed to feed past it through a small groove into the reservoir. At
the same time the slide valve covers the port to the brake cylinder, and
is in such a position that the air from the latter may exhaust into the
atmosphere. The piston has now the same air pressure on both sides; but
if the pressure in the brake pipe is decreased, the piston and slide
valve are forced down, thereby uncovering the passage through which air
from the reservoir flows into the brake cylinder between the pistons,
thus applying the brakes. The brake pipe is shut off as soon as the
triple valve piston passes the groove. To release the brakes, the piston
and slide valves are again moved into the position shown, by the driver
turning air from the main reservoir into the brake pipe. The air in the
brake cylinder escapes, and at the same time the reservoir is recharged.
[Illustration: THE WESTINGHOUSE BRAKE.]
Fig. 2 represents two Westinghouse couplings connected. They are exactly
alike in all respects, and an air tight joint is made between them by
means of the rubber washers. These couplings are so constructed that the
air pressure within serves to tighten the joint, and they may be pushed
apart by the separation of the train without any injury. Such an
occurrence as already explained leads to the instant application of all
the brakes on the train.
By closing the small tap shown between the brake pipe and the triple
valve, the brake on any vehicle, if out of order, can be cut out of the
system. A release valve is also placed upon each cylinder as shown, so
that in the event of the brakes being applied by the separation of
the train, or the breaking of a pipe, or when the locomotive is not
attached, they can be released by allowing the air to escape from each
brake cylinder direct. The Westinghouse brake has been made to comply
thoroughly with the Board of Trade conditions. Many people, however, do
not appear to understand all that is involved in the second requirement,
which runs as follows: In case of accident, to be instantaneously
self-acting. This clearly implies: First, that accident to the train,
or to any of its vehicles, shall cause the instant application of
the brakes to the wheels of every vehicle in the train without the
intervention of the driver or guards. Secondly, that any injury, however
caused, which may impair the efficiency of the brake apparatus, shall,
in like manner, lead to the instant application of all the brakes on
the train. It then becomes impossible for a driver to run his train in
ignorance of any defect in his brake apparatus because such defect at
once discloses itself by applying the brakes and stopping the train.
Thirdly, that each vehicle shall carry its own brake power in such a
manner that the destruction of the brake apparatus on one or more of the
carriages shall not affect the efficiency of the brakes upon any of the
others. No continuous brake which does not comply with such conditions
can ever be satisfactory.--_The Engineer_.
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