Illinois CDL Practice Exam

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Prepare for the Illinois CDL Exam. Utilize our comprehensive quiz featuring flashcards and multiple choice questions. Enhance your understanding and readiness for the exam with detailed explanations. Ace your CDL test and start your career in commercial driving!

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Why are shut-off valves installed in the air lines at the back of trailers?

To save fuel
To increase air pressure
To prevent air leakage
To close off air lines when not towing another trailer

The correct answer is: To close off air lines when not towing another trailer

Shut-off valves are installed in the air lines at the back of trailers primarily to efficiently manage the air supply when a trailer is not coupled to a towing vehicle. By closing off air lines, these valves prevent unnecessary air loss, which can help maintain air pressure levels within the system when the trailer is not in use. This is particularly important for trailers with air brakes, as it minimizes the risk of air leakage that could affect the braking system's performance when the trailer is reattached to a truck. In addition, shut-off valves help prevent contaminants from entering the air lines when a trailer is disconnected. This contributes to the overall maintenance and reliability of the air brake system, ensuring that it is ready for safe operation whenever the trailer is put back in service. Overall, this design feature reflects an understanding of how to maintain optimal conditions within the pneumatic system of the trailer.