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When towing doubles, how should the shutoff valves be set?
- A.All shutoff valves in the set should always be closed
- B.The valves at the rear of the front trailer (and dolly tank, where fitted) should be open to supply the units behind, while the shutoff valves at the rear of the last trailer should be closed
- C.Only the last trailer's rear valves should be open, to vent pressure
- D.Shutoff valves are set at the factory and never touched
Correct answer
B. The valves at the rear of the front trailer (and dolly tank, where fitted) should be open to supply the units behind, while the shutoff valves at the rear of the last trailer should be closed
Why
Air has to reach every unit in the set, so the path stays open through the front units, and it ends at the last trailer, whose rear valves stay shut to hold pressure in. A wrong valve leaves a rear trailer with no air and no brakes.
Manual topic: Combination Vehicles - Air Lines and Gladhands · From the Combination Vehicles practice bank (CV-244).