Air Brake Coach
TrailersQuestion 39 of 116

Why do you discharge air before you connect the glad hands?

  1. To raise the trailer pressure
  2. To test the governor
  3. To dry the seals
  4. To blow contamination out of the lines
Show answer

Correct answer: To blow contamination out of the lines

A quick discharge blows contamination out. It does not send the contamination into the trailer.

Source: Air Brake Manual: A Guide for Instructors (Government of Alberta, Alberta Transportation, March/April 2012), Module 6: Tractor and trailer circuits, page 61

Practice trailers

Questions last reviewed: 18 October 2026