TM 55-203
backing volume or driving head of excess pressure for
either directly or indirectly, must thoroughly understand
the purpose of releasing the brakes and recharging the
the elementary functions and operating principles of
airbrake system.
airbrakes.
Such an understanding is the largest
contributing factor to safety and economy and the
prevention of loss of life or damage to railroad rolling
d. Two duplex gages (located in locomotive cab),
stock and lading.
one indicating main reservoir and equalizing reservoir
pressure, the other, brake pipe and brake cylinder
b. Operation. The necessity for accurate and
pressure.
In addition, on dieselelectric passenger
locomotives with high-speed control brake equipment,
positive control of railway trains requires the use of
another single pointer gage in the cab shows control
efficient brakes and has led to the development of the
pipe pressure, while a single pointer gage in the engine-
modern airbrake. The use of airbrakes is compulsory on
room of each unit shows main reservoir pressure. On
American railways, and this apparatus has been
diesel-electric freight locomotives with No. 8 EL
developed to a high state of efficiency. The term
equipment, three duplex air gages are located in the
airbrakes includes any brake operated by air pressure,
cab, one indicating main reservoir and equalizing
but usually is restricted to systems of continuous brakes
reservoir pressure, a second indicating brake pipe and
operated by compressed air as generally used in
locomotive brake cylinder pressure, and a third
American railway practice to distinguish them from
indicating application and suppression pipe pressure. A
vacuum brakes. Air is compressed by a pump on the
single pointed gage indicating main reservoir pressure is
steam locomotive or by a motor compressor on electric
located in the engineroom of each unit.
or internal-combustion locomotives or cars stored in
reservoirs, and is conveyed by pipes and flexible hose
between the cars to cylinders and pistons under each
e. An automatic brake valve (located in locomotive
car. Under the cars the pressure is transmitted to the
cab), which regulates the flow of air from the main
brake levers and thence to the brakeshoes. The brakes
reservoirs into the brake pipe for releasing the brakes
are applied by reducing the pressure in the brake pipe
and from the brake pipe to the atmosphere for applying
below that in the auxiliary reservoirs. Such a reduction
the brakes. A feed valve controls and reduces main
is caused when the engineman opens the brake pipe to
reservoir pressure passing through the brake valve to
the atmosphere through the brake valve, or accidentally
the brake pipe in running position of the automatic brake
when a hose bursts or a pipe breaks. The brakes are
valve.
released by admitting compressed air from the main
reservoir on the locomotive through the brake valve into
f. A brake pipe (including branch pipe, flexible
the brake pipe, thus increasing the air pressure above
that remaining in the auxiliary reservoir.
automatic brake valve and the conductor's valve with
the brake control valve on each car. Angle cocks are
8-8.
Principal Parts of the Automatic Brake
provided at each end of every car for opening or closing
the brake pipe at any desired point in the train. Cutout
cocks are located in the branch pipe or crossover pipe to
the brake control valve under each car to cutout
compressed air for use in the brake and signal system.
individual brakes.
b. A governor, which controls compressor
g. A brake control valve on each car to which the
operation and regulates the air pressure maintained in
brake pipe, auxiliary reservoir, brake cylinder, and
the main reservoir.
pressure retaining valve are connected, which performs
three functions: first, to charge the auxiliary reservoir
c.
Main reservoirs, which serve three purposes:
from the brake pipe; second, to admit air from the
auxiliary reservoir to the brake cylinder to apply the
(1) To receive and store the compressed air.
brake; and third, to exhaust air from the brake cylinder
to the atmosphere to release the brake. The AB type
(2) To act as a cooling chamber for the
brake, used on freight cars operating in CONUS, is
compressed air and as a catch basin for moisture and oil
provided with an additional valve and reservoir which
which is passed from the compressor and precipitated
are used to provide additional braking power in
from the air by cooling.
emergency situations.
(3) To act as a storage chamber for express
h. An auxiliary reservoir (also an emergency
pressure for operating other air-using devices without
interfering with brake pipe pressure, and to serve as a
reservoir with the AB type brakes) on each car in which
compressed air is stored for applying the brakes.
8-10
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