Air Brakes

This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice.. Read More

This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice questions. Each question has three answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Rhode Island Commercial Driver License Manual. Questions come from the chapter covering: Air Brakes. The Air Brakes endorsement may be used with the Class A, B or C CDL.

Number of Question
Passing Score

7. What is often found in compressed air?

Explanation
Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Tanks must be drained regularly to remove this build-up.

8. A safety valve is set to open at ____ pounds per square inch (psi).

Explanation
The safety valve protects air tanks and the rest of an air brake system from accumulating too much air pressure. The safety valve is usually set to open at 150 psi.

9. Do not operate a vehicle if any brake drums have cracks that are larger than ____ of the width of the friction area.

Explanation
Before beginning a trip, it is important to check the brake drums during your walk-around inspection. It is unsafe to drive if any brake drum has a crack more than one half of the width of the friction area.

10. The ____ between an air compressor and reservoir tank prevents air from escaping if the air compressor has a leak.

Explanation
A one-way check valve is required to be between an air compressor and the first main reservoir. This valve prevents air from escaping the system if the air compressor develops a leak.

11. In a dual air brake system, air pressure should build from 85 to 100 psi within ____ seconds.

Explanation
When inspecting a vehicle with a dual air brake system, you should wait for air pressure to build from 85 to 100 psi in both the primary and secondary systems. This should take about 45 seconds.

12. Having ABS on only one axle:

Explanation
If you have an Anti-Lock Braking System (ABS) equipped on only the tractor, only the trailer, or only one axle, you will still have more control over the vehicle when braking than you would without ABS. You should brake normally.
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