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What is the difference between the trailer's emergency (supply) air line and its service air line?
- A.Both lines carry identical signals and can be swapped freely
- B.The emergency line supplies and charges the trailer air system, while the service line carries the brake application signal that tells the trailer brakes how hard to apply
- C.The service line charges the tanks and the emergency line is a spare
- D.The emergency line works only when the trailer is parked
Correct answer
B. The emergency line supplies and charges the trailer air system, while the service line carries the brake application signal that tells the trailer brakes how hard to apply
Why
The two lines have separate jobs, which is why their glad hands and seals must be connected correctly. Service braking on the trailer follows the pressure sent through the service line in proportion to the driver's pedal application.
Manual topic: Air Brakes - Trailer Air Brakes · From the Air Brakes practice bank (AB-235).