Practice question

What is the function of the relay valve in a semi-trailer's air brake system?

To disconnect the air lines automatically during a breakaway
To speed up the application and release of the trailer brakes by using local air reservoirs rather than relying solely on air traveling from the tractor cab
To pump exhaust gas back into the trailer suspension airbags
To switch the trailer lights from 12V to 24V automatically

Answer: B — To speed up the application and release of the trailer brakes by using local air reservoirs rather than relying solely on air traveling from the tractor cab

The correct answer is shown above. Try the full quiz for additional practice.