TM 55-203
placing the couplings on dummy coupling plugs.
8-30. Operation-Steam Locomotives
Atmospheric pressure forces the coupling gaskets to
seal on the plugs, thereby effectively closing the ends of
a. The train pipe and vacuum chambers are
the system.
carried at subatmospheric pressure during release and
running operations. The pressure on both sides of the
d. On heavy steam locomotives, it is customary to
brake cylinder piston is thus equalized, and the braking
use live steam in the driver brake cylinders and vacuum
force is removed from the brakeshoes. To apply the
brakes in the tender. The admission of steam to, and
brakes, the vacuum in the trainline is reduced by
the exhausting of steam from, the steam brake cylinders
admitting air from the atmosphere into the trainline.
is controlled by the engineman with the use of a steam
This inflow of air creates a difference in pressure across
brake attachment which is applied to the steam ejector.
the brake cylinder piston resulting in a force which is
transmitted through the brake rigging to the brakeshoes
8-31. Operation-Diesel-Electric Locomotives
to apply the brakes.
a. General. Diesel-electric locomotives to be used
b. A steam ejector on the locomotive uses steam
in single or multiple (MU) service handling vacuum-
at boiler pressure to create a vacuum in the vacuum
braked trains may be equipped with the Westinghouse
reservoirs and the train pipe until such time as it is
28-LV-1 brake equipment, a combined compressed air
desired to apply the brakes. The vacuum reduction
and vacuum brake. Thus, on trains equipped with
attachment of the steam ejector controls the amount of
vacuum brakes, the locomotive brakes are operated by
vacuum in the trainline to a constant maximum value
compressed air, either independently or in conjunction
irrespective of variations in steam pressure. Each brake
with the car brakes. In the latter case, the air system
cylinder is connected with one side of its piston open to
acts as a pilot for the train vacuum brakes.
the train-line and the other side open to a vacuum
chamber which is evacuated to correspond to trainline
b. Brake Application. When the locomotive and
conditions through a ball type check valve. To apply the
brakes, it is only necessary to partially reduce the
train brakes are applied, the automatic brake valve is
vacuum on the application side of the brake cylinder
moved into the service brake zone, permitting brake
piston without disturbing it on the vacuum chamber side.
pipe air pressure to drop at the desired service rate.
This is done by admitting air from the atmosphere into
The reduction in brake pipe pressure operates a control
the trainline. The maximum power is derived from the
valve to admit atmospheric air into the vacuum brake
brake cylinder by maintaining the vacuum on the
pipe. The destruction of vacuum in the vacuum brake
vacuum changer side of the piston and completely
pipe is in proportion to the air pressure brake pipe
destroying the vacuum in the trainline.
reduction made. The 28-V13 control valve responds to
the loss of vacuum in the vacuum brake pipe to apply
c. The vacuum system is made up of two separate
the locomotive brakes via the C-2 relay valve.
pipelines connected to the steam ejector. The first line
Simultaneously, the vacuum car brakes are applied due
is for the locomotive and tender only and connects the
to the destruction of vacuum via the VA-1-A control
vacuum reservoirs and the chambers above the brake
valve. On a vacuum-braked train after the desired air
cylinder piston to the vacuum chamber connection of
brake pipe reduction, the atmospheric air buildup in the
the steam ejector. The second line (the trainline) runs
VA-1-A control valve operates to cut off the flow of
the entire length of the train and is made up of
atmospheric air to the vacuum brake pipe. Thus, the
permanently fixed lines on each car, locomotive, and
control valve is lapped, holding the vacuum brakes
tender. The second line is coupled between the cars
applied. The VA-1-A control valve will automatically
with a flexible hose and coupling. This line is connected
maintain the desired degree of brake application against
to each car, and to all vacuum chambers through a ball
normal vacuum brake pipe leakage. Complete details
valve. The ends of the trainline, both at the head of the
of the operation of this equipment are contained in the
locomotive and at the rear of the last car, are closed by
manufacturer's instruction pamphlets.
8-60
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