Air Brake Coach
InspectionQuestion 73 of 116

At what pressure range must the trailer air supply valve (red button) pop out?

  1. 10 to 20 PSI
  2. 80 to 100 PSI
  3. 40 to 60 PSI
  4. 120 to 135 PSI
Show answer

Correct answer: 40 to 60 PSI

The practical test says the red button must pop out at 40 to 60 PSI (276 to 414 kPa) or higher.

Source: Air Brake Manual: A Guide for Instructors (Government of Alberta, Alberta Transportation, March/April 2012), Air Brake Practical Test (DPLS0003): Tractor protection system, page 123

Practice inspection

Questions last reviewed: 18 October 2026