Shutoff Valves

Shutoff valves, commonly known as cutoff cocks, are used in the service and emergency lines glad hands located on the back of military series tractors, cargo

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 opening and closing of the airlines when towing trailers.

Trailer Air Tanks

Trailers and dollies have one or more air tanks. The air tanks are filled by the emergency air line from the tractor. They provide the air pressure used to operate the trailer brakes by sending air pressure from the air tanks to the brakes via relay valves. The pressure in the service line signals how much pressure the relay valves should send to the trailer brakes. The pressure in the service line is controlled by the brake pedal and/or the trailer hand brake.

CAUTION

Do not allow water and oil to build up in the air tanks. Excessive amounts of water and oil affect the operation of the brakes negatively.

Each tank has drain valve that should be drained daily.

OPERATION

In the NCF, tractor-trailer operations are managed by the transportation supervisor. The operation of a tractor-trailer is much more difficult than that for most other vehicles; therefore, operators must be mature, reliable, and experienced.

To drive a tractor-trailer safely, you must be able to control its speed and direction. Safe operation of a tractor-trailer requires skill in coupling and uncoupling, accelerating, steering, shifting gears, and braking. Additionally, you must remember to make allowances for the added length when turning, backing, and passing other vehicles and for maneuvering into position for loading and unloading.