CDL Air Brakes Practice Test 1 — Questions and Answers
Question 1: What type of air do air brakes use?
- Decompressed air
- Warm air
- Compressed air (Correct answer)
- Heated air
Correct answer: Compressed air
Air brake systems operate by using compressed air, which is stored in tanks and then released to activate the brake components. An air compressor builds up the pressure, and when the driver presses the brake pedal, this compressed air is directed to the brake chambers, applying force to stop the vehicle.
Question 2: What are the three types of brake systems used in a commercial vehicle air brake system?
- Hand brake, parking brake, emergency brake
- Service brake, parking brake, emergency brake (Correct answer)
- Anti-lock brake, service brake, emergency brake
- Service brake, hand brake, emergency brake
Correct answer: Service brake, parking brake, emergency brake
Commercial vehicles with air brakes utilize three distinct braking systems. The service brake is used for normal stopping, the parking brake holds the vehicle stationary when parked, and the emergency brake system uses parts of the service and parking brake systems to stop the vehicle in case of a service brake failure. These systems work together to ensure safe operation and parking.
Question 3: What is the name of the device that pumps air into the air storage tanks?
- Governor
- Evaporator
- Safety valve
- Air compressor (Correct answer)
Correct answer: Air compressor
The air compressor is a vital component of an air brake system, responsible for drawing in air from the atmosphere and compressing it. This compressed air is then stored in the air tanks, providing the necessary pressure to operate the vehicle's brakes and other air-powered accessories.
Question 4: What is the alcohol evaporator's primary purpose?
- Remove water and oil from the air brake system
- Remove alcohol from the air brake system
- Put alcohol into the air system (Correct answer)
- To heat the air tank
Correct answer: Put alcohol into the air system
An alcohol evaporator, found in some older air brake systems, is designed to inject alcohol vapor into the air lines. This alcohol helps prevent moisture in the air system from freezing during cold weather, which could otherwise cause brake components to malfunction and lead to brake failure.
Question 5: What psi level is the safety relief valve set to open at?
- 150 psi (Correct answer)
- 125 psi
- 60 psi
- 100 psi
Correct answer: 150 psi
The safety relief valve is a crucial safety device in the air brake system, designed to protect the air tanks and other components from excessive pressure. It is typically set to open and release air if the pressure in the system exceeds 150 psi, preventing damage or rupture of the air tanks.
Question 6: Which of the following is the most common type of foundation brake?
- Wedge brake
- S-cam drum brake (Correct answer)
- Disc brake
- Anti-lock brake
Correct answer: S-cam drum brake
The S-cam drum brake is the most prevalent type of foundation brake found on heavy-duty commercial vehicles. When air pressure is applied, the S-cam rotates, forcing the brake shoes against the inside of the brake drum, creating friction to slow or stop the vehicle. Its robust and reliable design makes it ideal for commercial applications.
Question 7: Which of the following statements is true regarding front wheel braking?
- Front wheel braking is good under all conditions (Correct answer)
- Front wheel braking will cause skids on ice
- You should put a front brake limiting valve (if equipped) on the slippery position in adverse conditions
- Front wheel braking is ineffective in slippery conditions
Correct answer: Front wheel braking is good under all conditions
Modern commercial vehicles are designed with front wheel brakes that are effective and necessary for optimal stopping power under all conditions. While older systems might have had front brake limiting valves for slippery conditions, current regulations and designs ensure front brakes contribute significantly to overall braking performance without causing skids when properly maintained and operated.
Question 8: At what air pressure must the low air pressure warning signal come on?
- 150 psi
- 50 psi
- 45 psi
- 60 psi (Correct answer)
Correct answer: 60 psi
Federal regulations mandate that the low air pressure warning signal must activate when the air pressure in the service air tanks falls below 60 psi (or half the governor cut-out pressure on older vehicles). This warning alerts the driver to a critical loss of air pressure, indicating a potential problem with the air brake system that requires immediate attention.
Question 9: Which of the following statements regarding spring brakes is true?
- Spring brakes will come on at 60 psi
- Spring brakes are held by mechanical force (Correct answer)
- Spring brakes use air pressure to stop a vehicle
- Spring brakes will not function if the system loses air pressure
Correct answer: Spring brakes are held by mechanical force
Spring brakes are designed to engage mechanically by spring force when air pressure is lost or intentionally released (e.g., when parking). Air pressure is actually used to hold them open (compress the springs) when the vehicle is in operation. If air pressure drops too low, the springs expand, applying the brakes automatically as an emergency and parking brake.
Question 10: Which of the following devices indicates how much pressure you have in your air tanks?
- Application pressure gauge
- Low air pressure warning signal
- Ammeter
- Supply pressure gauge (Correct answer)
Correct answer: Supply pressure gauge
The supply pressure gauge displays the amount of air pressure stored in the primary and secondary air tanks. This gauge is crucial for the driver to monitor the system's air supply, ensuring there is sufficient pressure for safe braking and operation of other air-powered accessories.
CDL Air Brakes Practice Test 1
What type of air do air brakes use?