CLP - Commercial Learner's Permit Air Brake Systems Questions and Answers 1 — Questions and Answers
Question 1: During a static air brake leakage test on a single vehicle, what is the maximum permissible pressure drop in one minute?
- 1 psi
- 2 psi (Correct answer)
- 3 psi
- 4 psi
Correct answer: 2 psi
For a single vehicle, the air pressure should not drop more than 2 psi in one minute during a static leakage test (engine off, brakes released). For a combination of two vehicles, the limit is 3 psi.
Question 2: A driver is performing an air brake check. At what pressure range should the low air pressure warning light and buzzer activate?
- Below 100 psi
- Between 80 and 90 psi
- At or before 55-60 psi (Correct answer)
- Between 20 and 45 psi
Correct answer: At or before 55-60 psi
The low air pressure warning signal (light and/or buzzer) must activate at a pressure of 55 psi or higher, and generally before the pressure drops below 60 psi. This alerts the driver to a potential issue before the spring brakes automatically engage.
Question 3: In a vehicle with a properly functioning dual air brake system, what is the expected time for the air compressor to build pressure from 85 to 100 psi?
- Within 15 seconds
- Within 30 seconds
- Within 45 seconds (Correct answer)
- Within 60 seconds
Correct answer: Within 45 seconds
For dual air systems, the air pressure should build from 85 to 100 psi within 45 seconds with the engine at normal operating RPMs. A longer time may indicate a problem with the air compressor.
Question 4: A driver is operating a truck-tractor with a trailer. While driving, the low air pressure warning comes on. What is the safest immediate course of action?
- Continue driving to the nearest service station.
- Pump the brake pedal to try and build pressure.
- Increase speed to let the compressor work faster.
- Pull over and stop in the safest possible location. (Correct answer)
Correct answer: Pull over and stop in the safest possible location.
When the low air pressure warning activates, it signifies a critical loss of air pressure that could lead to brake failure. The safest and required action is to stop the vehicle as soon as safely possible to diagnose and fix the issue.
Question 5: Which of the following brake systems is primarily responsible for applying and releasing the brakes when you use the foot pedal during normal driving?
- Emergency brake system
- Parking brake system
- Service brake system (Correct answer)
- Spring brake system
Correct answer: Service brake system
The service brake system is the primary system used for slowing or stopping the vehicle during normal driving. It is controlled by the foot brake pedal (also called the treadle valve).
Question 6: If air pressure drops into the 20-45 psi range, what is most likely to occur?
- The air compressor will turn on.
- The service brakes will become more sensitive.
- The tractor protection valve and/or parking brake valve will pop out.
- The low-pressure warning light will turn off. (Correct answer)
Correct answer: The low-pressure warning light will turn off.
When the air pressure drops to a critically low level, typically between 20 and 45 psi, the spring brakes will automatically apply. This is caused by the parking brake valve and, on combination vehicles, the tractor protection valve closing (popping out).
CLP - Commercial Learner's Permit Air Brake Systems Questions and Answers 1
During a static air brake leakage test on a single vehicle, what is the maximum permissible pressure drop in one minute?