CDL Air Brake - Commercial Driver's License Air Brakes Dual Air Brake Systems Questions and Answers — Questions and Answers
Question 1: What is the primary safety advantage of a dual air brake system?
- It allows the vehicle to stop in a shorter distance than a single system.
- It eliminates the need for spring brakes.
- It provides braking capability even if one of the two systems fails. (Correct answer)
- It uses a single air tank, making it easier to maintain.
Correct answer: It provides braking capability even if one of the two systems fails.
A dual air brake system is designed with two separate, independent systems. If one system develops a major leak or fails, the other system is isolated and can still provide enough braking force to bring the vehicle to a safe stop.
Question 2: A driver is operating a vehicle with a dual air brake system. The low air pressure warning light and buzzer activate. What is the minimum pressure remaining in the system for this to occur?
- At approximately 100 psi
- At or above 125 psi
- Before pressure drops below 60 psi (Correct answer)
- When the pressure drops between 20-45 psi
Correct answer: Before pressure drops below 60 psi
The low air pressure warning light and buzzer must come on before the air pressure in either the primary or secondary system drops below 60 psi. This gives the driver an early warning of a potential issue with the air supply.
Question 3: When conducting a pre-trip inspection on a dual air brake system, what is the minimum air pressure the compressor should build in both the primary and secondary systems before driving?
- 60 psi
- 85 psi
- 125 psi
- 100 psi (Correct answer)
Correct answer: 100 psi
Before driving, you must allow the air compressor to build up a minimum of 100 psi in both the primary and secondary systems. This ensures sufficient pressure is available for normal braking operations.
Question 4: In a typical dual air brake system on a two-axle truck, how are the two systems usually split?
- One system operates the left side brakes and the other operates the right side brakes.
- One system operates the front axle, and the other operates the rear axle. (Correct answer)
- Both systems operate all brakes simultaneously, with one as a backup.
- One system operates the service brakes and the other operates the parking brake.
Correct answer: One system operates the front axle, and the other operates the rear axle.
Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle. This separation ensures that if one system fails, the other can still provide braking on at least one axle.
Question 5: While driving a truck with a dual air brake system, a failure occurs in the primary system. Which of the following is the most likely outcome?
- The parking brake will immediately apply automatically.
- The brake pedal will feel solid, but the truck will not stop.
- Both front and rear brakes will lose all braking power.
- Stopping distance will be increased, and the secondary system will still provide braking. (Correct answer)
Correct answer: Stopping distance will be increased, and the secondary system will still provide braking.
If one of the air systems in a dual system fails (e.g., the primary system), the other system (secondary) is unaffected and will continue to operate the brakes on its axle(s). However, with only half of the service brakes working, the vehicle's total stopping distance will increase.
Question 6: During a static leak test with the brakes fully applied on a single vehicle with a dual air brake system, the air loss rate should not exceed:
- 1 psi in one minute
- 2 psi in one minute
- 3 psi in one minute (Correct answer)
- 4 psi in one minute
Correct answer: 3 psi in one minute
According to the FMCSA guidelines for an applied brake leakage test on a single vehicle, the air pressure should not drop more than 3 psi in one minute after the initial pressure drop.
CDL Air Brake - Commercial Driver's License Air Brakes Dual Air Brake Systems Questions and Answers
What is the primary safety advantage of a dual air brake system?