6.5. THE AB AIRBRAKE
Most freight cars are now equipped with the AB airbrake system diagramed in figure 6.2. By comparing
figures 6.1 and 6.2, you can see that the reservoir, valve, and brake cylinder are mounted separately in the AB
system rather than together as in the KC. Notice also in the AB system that the reservoir under each car is
divided into two parts by a separator plate; one side is the auxiliary reservoir, and the other side is the
emergency reservoir. The AB, like the KC, has a triple valve that performs the same three basic functions: it
charges the reservoirs, directs air to the brake cylinder to apply the brakes, and exhausts air from the system to
release them. Instead of three pipe connection, it has five: one to each side of the reservoir, one to the brake
cylinder, one to the release control retainer, and one to the dirt collector on the branch pipe.
The AB airbrake system has several advantages over the KC system. It provides for quicker application
and release of the brakes, is capable of instant emergency application of the brakes that increases the braking
ability by 20 percent, and has an air filter in the triple valve that catches minute particles of dust not trapped in
the dirt collector. This final advantage prolongs the time between maintenance overhauls.
6.6. PARTS OF THE BRAKING SYSTEMS
Now that the three basic airbrake systems have been discussed generally, let's find out the names,
locations, and functions of the parts that make up each system. However, before beginning, let's narrow the
field to two systems by eliminating the straight airbrakes; this system is simple and has few parts when
compared with the KC and AB systems. The other two systems are much more complicated and involve many
parts; the most important are discussed in the following subparagraphs. As you follow these discussions, refer
to figures 6.1 and 6.2.
a. The train line is a combination of hoses and pipes that, when coupled together at both ends of the car,
form a continuous air line from the locomotive reservoir or air supply to the end of the train. At each end of this
line, on each car, a section of flexible hose is connected. A hose connection or coupling is attached that mates
with that of other cars.
b. The angle cock is a two-position valve that is open when its handle is parallel with the train line and
closed when the handle is