_THE EAMES VACUUM BRAKE._
OPERATION OF THE BRAKE.
The Vacuum Brake, as the name implies, is operated by means of a vacuum
which is formed in the connections that act the part of the cylinder
in the air-brake. With an air-brake, compressed air is made to do the
work of applying the brakes by moving a piston to which the brake-lever
is attached, the air being carried throughout the train by means of
iron pipes and rubber hose: with the vacuum brake the work is done in
a similar way with similar connections; but, instead of compressed air
being forced inside the pipes and apparatus, all the air is exhausted
out, and the natural pressure of the atmosphere is made to do the work.
THE DIAPHRAGM.
[Illustration: FIG. 35.]
Under each vehicle of a train, as seen in Fig. 35, a diaphragm is
securely fastened which performs the combined duties of cylinder and
piston. It consists of a kettle-shaped casting with a loose disk of
heavy rubbered duck fastened over its mouth; the center of the disk
being provided with an iron plate, through which passes an eye-bolt for
forming connection with the brake-lever. The inside of the diaphragm
is connected to the pipe which passes along the train, and has its
front end connected with the ejector on the locomotive.
THE EJECTOR.
[Illustration: FIG. 36.]
The position of the ejector in the cut can be clearly seen in Fig. 36,
where there is also a diaphragm to be seen under the deck where it is
located when used to operate driver brakes. The ejector is operated
on the same principle as the water injector, only it is used to lift
air instead of water. A cross-section of the injector is shown in
Fig. 36. When the engineer wishes to apply the brake, he pulls the
handle 41 (broken off in the cut), which opens the valve _B49_, and
admits steam to the body of the ejector _A1_. The steam rushes upward
round the end of the tube 5, its velocity being accelerated in
passing through the contracted opening left round the top of the tube.
Passing through tubes 3 and 6, the steam shoots up in the form of a
column with a hollow base; the tube 5, which is connected with the
pipes and diaphragms on the train, forming this base. The effect of
the steam passing out under these conditions is to induce a current
through the tube 5, which draws up the valve _B7_, and sucks the air
out of the pipes and diaphragms. A vacuum being thus formed in the
diaphragms, the atmosphere presses the flexible ends together. This
tendency to collapse is retarded by the brake-rod connections, and the
latter receive a pull equal to the combined atmospheric pressure on the
diaphragm. The brake-levers are arranged to transmit a proper tension
to the brake-shoes for making the brake effective. A vacuum gauge
placed on the front of the ejector enables the engineer to regulate the
power as he wants it. The brake is released by pushing on the lever
24, which opens the valve 8, and admits air into the brake-pipes. The
release-valve attachment is sidewise in vertical section cut through
the handle, and is put separate for convenience of illustration.
CARE OF THE BRAKE.
The valve _B7_ of the ejector needs grinding occasionally; and, if
the lift should be too great, the valve will hammer the seat out of
shape. Sometimes when waste or other fibrous impurities are sucked
through the pipe, they stick in this valve, keeping it away from the
seat. The valve is very easily reached by taking off the cap _O4_. The
steam-valve _B49_ needs about the same care as any other steam-valve,
and its troubles are of the same nature. The shoulder at the top of the
tube 5, which is used to obstruct the steam, thereby increasing the
velocity of the quantity that passes, sometimes gets cut into channels
with the fast moving steam striking it. This reduces the promptness of
the ejector’s action, but it is a form of deterioration that proceeds
very slowly. Care must be taken to keep the drip-valves _A_ and _B16_
in order, otherwise there may be trouble with the ejector throwing
water, or freezing up if the engine stands where that apparatus will
get cold in winter.