CDL · Combination vehicles
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?
Correct answer: 20 to 45 psi.
Answer options
- A20 to 45 psi Correct
- B100 to 125 psi
- C60 to 80 psi
Why
Manufacturers typically set the valve to close somewhere between 20 and 45 psi. When it closes, it holds the remaining air in the tractor (or truck) brake system, so a trailer that breaks away or leaks badly cannot drain it.
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
- In which situation may a parked combination vehicle be held by the trailer hand valve alone?
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- Before your tractor goes under the trailer, what condition must the entire air system be in?
- During coupling, your tractor is in front of the semitrailer but not yet under it. What do you connect before backing under?
- How do you get air flowing into the trailer's air tanks?
- When you drive a tractor with no trailer attached, why should its glad hands be locked together or onto dummy couplers?
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