d. Lap. This term designates the position of the
i. A brake cylinder or cylinders on each car,
locomotive brake valve and brake control valves or
provided with a piston rod connected with the brake
distributing valve, in which all operative parts are closed
levers in such a manner that when the piston is moved
to the passage of air.
by air pressure the brakes are applied.
Brake Application. A sufficient reduction of
j. A pressure-retaining valve that permits the
brake pipe pressure (no matter how made) to cause the
brake cylinder air to be freely exhausted to the
brake control valves, or distributing valve, to move to
atmosphere or retards the exhaust of air from the brake
application position. If made with the locomotive brake
cylinder down to a predetermined pressure and then
valve in service position, it may consist of one or more
retains that amount.
reductions with brakes remaining applied.
Definition of Term Used
f. Service Application. A quick, heavy reduction of
brake pipe pressure so as to cause the brake control
a. Increase In Brake Pipe Pressure. When air is
valves to move to service application position. This
passing into the brake pipe more rapidly than it is
condition is accomplished by the locomotive engineer
escaping, so as to produce a rise in pressure (brake pipe
for an expected stop or slow down or when a gradual
pressure increase), it will move the control valves to
reduction is made with the conductor's valve or tail
b. Maintaining Brake Pipe Pressure. With the
g. Emergency Application.
A quick heavy
automatic brake valve in running position, air is being
reduction of brake pipe pressure which will cause the
supplied to the brake pipe as fast as it is escaping. The
brake control valves to move to emergency position and
feed valve automatically supplies brake pipe losses.
transmit quick action. This condition is accomplished
when the locomotive brake valve is placed in
c. Brake Pipe Reduction. Air is escaping or being
emergency position, or by the trainmen with the
discharged from the brake pipe faster than it is being
conductors valve or tail hose.
It is also made
supplied through the brake valve, or feeding back from
automatically when the brake pipe is broken or when the
the auxiliaries. Losses from the brake pipe that are not
being supplied will constitute a brake pipe reduction and
tend to cause the brake control valves to move toward
Section IV. AB FREIGHT BRAKE EQUIPMENT
4-12 and the AB Automatic Empty and Load brakes are
practically the same as the AB brakes with minor
a. In 1926, the Association of American Railroads
variations. Therefore, only the AB and AB-1-B brakes
Commission inaugurated a series of tests of various
types of airbrake equipment for freight train brakes.
Rack tests were followed by road tests. These resulted
a. AB Freight Brake. The AB freight brake was
in adoption of an approved freight brake which has been
developed to keep pace with other major improvements.
given the designation AB. Additional equipment now
All of the good operating features of the standard brake
have been retained and other valuable ones added.
The AB brake has been adopted by the Association of
(1) AB-1-B brake equipment for highspeed
American Railways (A.A.R.) as standard freight brake.
freight or passenger service.
Following are some of the approved features in the AB
brake that were not included in the K freight brake.
(2) AB-4-12 brake equipment for heavy freight
(1) Improved quick service. The three stages
of quick service provide a prompt and positive brake
(3) AB Automatic Empty and Load brake
application on all cars of long modern trains.
equipment used generally on high-capacity gondola and
hopper cars operating primarily in coal or ore service
(2) Improved release. In case of excessive
where they operate empty or fully loaded.
slide valve friction that may delay release (or cause a
struck brake), a release insuring valve
The performance and maintenance of the AB-