Free Air Brake Questions and Answers — Questions and Answers
Question 1: What produces the air necessary for an air brake system to function?
- Under-hood compressor (Correct answer)
- External compressor
- Recumbent air pressure
- Pre-compressed cylindered air
Correct answer: Under-hood compressor
An air brake system relies on compressed air to operate. The 'under-hood compressor,' also known as the air compressor, is the component specifically designed to draw in air, compress it, and then store it in reservoirs for use by the braking system. This ensures a continuous supply of pressurized air for safe vehicle operation.
Question 2: What is the typical operating pressure range of air brake systems?
- 90-100 PSI
- 180-200 PSI
- 105-125 PSI (Correct answer)
- 50-90 PSI
Correct answer: 105-125 PSI
Commercial vehicle air brake systems are designed to operate within a specific pressure range to ensure optimal braking performance and safety. The typical operating pressure for these systems is between 105 and 125 PSI. This range allows for effective brake application while preventing over-pressurization.
Question 3: When should the low-pressure warning system activate?
- 30 PSI
- 10 PSI
- 50 PSI
- 60 PSI (Correct answer)
Correct answer: 60 PSI
The low-pressure warning system is a critical safety feature in air brake systems, designed to alert the driver to a potential problem. It is mandated to activate when the air pressure in the system drops below 60 PSI. This warning ensures the driver is aware of insufficient air pressure before it becomes dangerously low, allowing time to address the issue.
Question 4: In a hand-pull test, how much push rod travel is necessary for the brakes to work?
- 1/4 inch
- 1 inch
- 1/2 inch (Correct answer)
- 3/4 inch
Correct answer: 1/2 inch
The hand-pull test, or manual slack adjuster check, is used to verify that the brakes are properly adjusted. For the brakes to work effectively and safely, the push rod travel should not exceed 1/2 inch when the brakes are applied. Excessive travel indicates that the slack adjuster needs adjustment, which could lead to reduced braking efficiency.
Question 5: What is the name for using the parking brakes or "spring" in an emergency?
- Travelling
- Exploding
- Engaging
- Dynamiting (Correct answer)
Correct answer: Dynamiting
In the context of air brake systems, 'dynamiting' refers to the emergency application of the parking brakes, which are spring-activated. This term is used because it describes the sudden, forceful engagement of the spring brakes when air pressure is lost or intentionally released in an emergency, providing maximum stopping power.
Question 6: What would happen if your service line burst while you were towing a trailer with air brakes?
- Your brakes would become ineffective
- Your tractor would lose all air pressure from the reservoirs
- Your trailer brakes would make an emergency application
- Nothing, unless you made a service brake application (Correct answer)
Correct answer: Nothing, unless you made a service brake application
The service line (or control line) carries air pressure from the tractor's foot valve to the trailer's relay valve, controlling the trailer's service brakes. If this line bursts, air pressure cannot reach the trailer's service brakes when the foot valve is pressed. Therefore, the trailer brakes would not apply *only* when a service brake application is made, but the trailer's emergency brakes (spring brakes) would not automatically apply from a service line burst alone.
Question 7: What would happen if you were towing a trailer and the supply line burst?
- Spring brakes would make an emergency application (Correct answer)
- Nothing
- Tractor spring brakes would make an emergency application
- Tractor would lose all air pressure from the secondary reservoir
Correct answer: Spring brakes would make an emergency application
The supply line (or emergency line) provides constant air pressure to the trailer's air tanks and holds off the trailer's spring (emergency) brakes. If the supply line bursts, the air pressure holding off the trailer's spring brakes is lost, causing them to automatically engage in an emergency application. This is a crucial safety feature designed to stop the trailer if it separates or loses air supply.
Question 8: How can one minimize brake lag and apply the brakes more quickly by keeping an air supply close to the rear service brakes?
- Supply valve
- Rear reservoir
- Relay valve (Correct answer)
- Automatic slack adjuster
Correct answer: Relay valve
A relay valve is used in air brake systems, particularly on longer vehicles or trailers, to reduce brake lag. It acts as a remote-controlled valve, allowing a large volume of air from a nearby reservoir to be quickly directed to the brake chambers. This minimizes the time it takes for air to travel from the foot valve to the rear brakes, ensuring a more immediate and effective brake application.
Question 9: What happens with a dual circuit air brake system if the air supply to the primary reservoir is cut off?
- The vehicle will still have braking power (Correct answer)
- The tractor brakes will dynamite
- The vehicle will not have any braking power
- The tractor protection valve will not allow the reservoir to lose any pressure
Correct answer: The vehicle will still have braking power
A dual circuit air brake system is designed with two separate air systems, each capable of providing braking power. If the primary reservoir's air supply is cut off, the secondary circuit will still function, ensuring the vehicle retains sufficient braking power to stop safely. This redundancy is a critical safety feature in commercial vehicles.
Question 10: What stops air from returning to the compressor from the reservoir?
- Tractor protection valve
- One way check valve (Correct answer)
- Two way check valve
- Relay emergency valve
Correct answer: One way check valve
A one-way check valve is installed between the air compressor and the air reservoirs. Its purpose is to allow compressed air to flow from the compressor into the reservoirs, but prevent it from flowing back out. This ensures that the air tanks maintain pressure even if the compressor stops or develops a leak, preserving the air supply for braking.
Question 11: What does the word "compounding" mean?
- Having more than one reservoir
- Applying the service brakes and using the hand valve at the same time
- Making a service brake application with the spring brakes engaged (Correct answer)
- Having the tractor and trailer spring brakes engaged at the same time
Correct answer: Making a service brake application with the spring brakes engaged
Compounding refers to the dangerous practice of applying both the service brakes (foot pedal) and the spring (parking/emergency) brakes simultaneously. This action can overload and damage the brake components, as the forces from both systems work against each other. It's crucial to only use one braking system at a time for safe and effective braking.
Free Air Brake Questions and Answers
What produces the air necessary for an air brake system to function?