Air Brake Coach
TrailersQuestion 34 of 116

What does the tractor protection valve use to open the service line?

  1. Hand valve pressure
  2. Spring pressure
  3. Foot valve pressure
  4. Supply line pressure
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Correct answer: Supply line pressure

The red button controls the supply line. The tractor protection valve uses supply line pressure to open the service line.

Source: Air Brake Manual: A Guide for Instructors (Government of Alberta, Alberta Transportation, March/April 2012), Module 6: Tractor and trailer circuits, page 63

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Questions last reviewed: 18 October 2026