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What is the job of the emergency (supply) air line to the trailer?
- A.It carries the brake pedal signal for normal stops
- B.It only supplies air to the trailer's air suspension bags
- C.It vents the trailer tanks to the atmosphere
- D.It charges the trailer's air tanks and controls the trailer's spring (emergency) brakes, releasing them when pressure is up and applying them if pressure is lost
Correct answer
D. It charges the trailer's air tanks and controls the trailer's spring (emergency) brakes, releasing them when pressure is up and applying them if pressure is lost
Why
The supply line is the trailer's lifeline: lose its pressure and the trailer's spring brakes apply automatically. That fail-safe design is why a separated trailer stops itself instead of rolling free.
Manual topic: Combination Vehicles - Air Lines and Gladhands · From the Combination Vehicles practice bank (CV-237).