Figure 7-12.Vehicle trailer hookup with glad hand cutoff cock.
Figure 7-13.Fifth wheel assembly.
trucks, and trailers (fig. 7-12). These valves permit the
tractor. They provide the air pressure used to operate the
opening and closing of the airlines when towing trailers.
trailer brakes by sending air pressure from the air tanks
to the brakes via relay valves. The pressure in the service
Trailer Air Tanks
line signals how much pressure the relay valves should
send to the trailer brakes. The pressure in the service line
Trailers and dollies have one or more air tanks. The
is controlled by the brake pedal and/or the trailer hand
air tanks are filled by the emergency air line from the