CDL · Combination vehicles
Before your tractor goes under the trailer, what condition must the entire air system be in?
Correct answer: Built up to normal pressure.
Answer options
- ABuilt up to normal pressure Correct
- BDrained to half of its maximum pressure
- CHeld somewhere in the 60 to 80 psi range
Why
The trailer brakes need a full supply of air to work properly during coupling, so let the pressure build to its normal level first. With low pressure, the brakes may not apply or hold the way they should.
About this question
Topic: Combination vehicles License: CDL
Part of these practice sets:
Where it applies: Asked in every state.
Practice the whole set
This question is part of Trailer Air Lines and Coupling (28 questions). Take the full set and check your score.
Practice Trailer Air Lines and CouplingMore questions from Trailer Air Lines and Coupling
- How do you get air flowing into the trailer's air tanks?
- After coupling to a semitrailer, how should you leave the landing gear (front trailer supports) before pulling away?
- What kind of equipment are glad hands?
- In which situation may a parked combination vehicle be held by the trailer hand valve alone?
- A fifth wheel plate that is not kept properly greased can lead to which problem?
- As air pressure drops, a tractor protection valve shuts by itself at a level set by its manufacturer. That level usually falls within which range?
- Many combination vehicles use color-coded air lines so the two are not confused. Which colors are typically used?
- Which sequence is correct for testing the trailer service brakes?
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