Practice question

For the Washington CDL Air Brakes knowledge test, what is the function of the relay valve in trailer air brake systems?

  1. It speeds up the application and release of air to the trailer brake chambers because the chambers are far from the foot valve
  2. It cools the brake drums
  3. It dries the air
  4. It applies the parking brakes

Answer: A — It speeds up the application and release of air to the trailer brake chambers because the chambers are far from the foot valve

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