Podcast
Questions and Answers
What are the three different systems that modern air brake systems combine?
What are the three different systems that modern air brake systems combine?
- Parking brakes
- Service brakes
- Emergency brakes
- All of the above (correct)
When should you drain the air tanks if you do not have an automatic tank drain?
When should you drain the air tanks if you do not have an automatic tank drain?
After every working day.
Why is it important to drain water from the compressed air tanks?
Why is it important to drain water from the compressed air tanks?
Water can freeze in cold weather and cause brake failure.
What must air brake equipped vehicles have?
What must air brake equipped vehicles have?
What can legally hold a parking or emergency brake in position for a truck, truck tractor, or bus?
What can legally hold a parking or emergency brake in position for a truck, truck tractor, or bus?
Air loss in a straight truck or bus should not be more than how much with the engine off and the brakes on?
Air loss in a straight truck or bus should not be more than how much with the engine off and the brakes on?
What should you do to make an emergency stop with air brakes using the stab braking method?
What should you do to make an emergency stop with air brakes using the stab braking method?
How do you know your brakes are fading?
How do you know your brakes are fading?
To check the free play of manual slack adjusters on s-cam brakes, what should you do?
To check the free play of manual slack adjusters on s-cam brakes, what should you do?
What keeps the air in the tanks if the air compressor develops a leak?
What keeps the air in the tanks if the air compressor develops a leak?
When driving down a long steep hill, what should you do?
When driving down a long steep hill, what should you do?
What brake system applies and releases the brakes when the driver uses the brake pedal?
What brake system applies and releases the brakes when the driver uses the brake pedal?
What is the most common type of foundation brakes found on heavy vehicles?
What is the most common type of foundation brakes found on heavy vehicles?
What must vehicles with air brakes have?
What must vehicles with air brakes have?
At what pressure level must a driver be able to see a warning before air pressure in the service air tanks falls?
At what pressure level must a driver be able to see a warning before air pressure in the service air tanks falls?
What makes the total stopping distance for air brakes longer than that for hydraulic brakes?
What makes the total stopping distance for air brakes longer than that for hydraulic brakes?
What is the first thing to do when a low air pressure warning comes on?
What is the first thing to do when a low air pressure warning comes on?
The braking power of the spring brakes depends on what?
The braking power of the spring brakes depends on what?
What does the air compressor governor control?
What does the air compressor governor control?
What does the application pressure gauge show the driver?
What does the application pressure gauge show the driver?
If your vehicle has an alcohol evaporator, what should you do every day during cold weather?
If your vehicle has an alcohol evaporator, what should you do every day during cold weather?
During normal driving, how are spring brakes usually held back?
During normal driving, how are spring brakes usually held back?
Why does air braking take more time than hydraulic braking?
Why does air braking take more time than hydraulic braking?
When should parking brakes be used in air brake vehicles?
When should parking brakes be used in air brake vehicles?
What does the brake pedal in an air brake system control?
What does the brake pedal in an air brake system control?
If your truck or bus has dual parking control valves, what can you use pressure from a separate tank to do?
If your truck or bus has dual parking control valves, what can you use pressure from a separate tank to do?
A straight truck or bus air brake system should not leak at a rate of more than how much PSI per minute with the engine off and the brakes released?
A straight truck or bus air brake system should not leak at a rate of more than how much PSI per minute with the engine off and the brakes released?
What is the purpose of an alcohol evaporator in your vehicle?
What is the purpose of an alcohol evaporator in your vehicle?
If you must make an emergency stop, how should you brake?
If you must make an emergency stop, how should you brake?
If your truck or bus has a dual air brake system and a low air pressure warning comes on for only one system, what should you do?
If your truck or bus has a dual air brake system and a low air pressure warning comes on for only one system, what should you do?
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Study Notes
Air Brake System Overview
- Modern air brake systems integrate service brakes, parking brakes, and emergency brakes.
- An air pressure gauge is mandatory for vehicles equipped with air brakes to monitor pressure available for braking.
Maintenance and Safety
- Drain compressed air tanks after each working day to prevent water condensation, which can freeze and cause brake failure.
- If equipped with an alcohol evaporator, check and fill the alcohol level daily during cold weather to minimize ice formation in air brake valves.
Performance Indicators
- A loss of no more than 3 psi in one minute is acceptable for straight trucks or buses with the engine off and brakes on.
- Parking and emergency brakes should be held in position by spring pressure.
Emergency Procedures
- To execute an emergency stop using stab braking, apply brakes hard, release when wheels lock, and reapply when wheels begin to roll again.
- The first response to a low air pressure warning is to stop and safely park as soon as possible.
Braking Dynamics
- The service brake system activates and releases brakes upon driver input via the brake pedal.
- Brake lag distance contributes to longer stopping distances for air brakes compared to hydraulic brakes due to the need for air to flow through lines.
Usage Guidelines
- Release brakes when descending a long steep hill when 5 mph below your safe speed.
- Parking brakes must be engaged whenever the vehicle is parked, ensuring safety during stops.
Adjustments and Controls
- Manual slack adjusters on S-cam brakes require checking free play by parking on level ground, chocking wheels, and releasing parking brakes.
- Air compressor governors regulate when air is pumped into the air tanks.
Operational Mechanisms
- Spring brakes rely on the proper adjustment of service brakes for effective braking power.
- The application pressure gauge indicates how much brake pressure is being applied by the driver.
System Reliability
- A one-way check valve is crucial to retain air in the tanks if the air compressor develops a leak.
- Vehicles with dual parking control valves can use pressure from a separate tank to release spring brakes for short movements.
Leak Standards
- Air brake systems on straight trucks or buses should not exceed a leak rate of 2 psi per minute when the engine is off and brakes are released.
- During normal driving, spring brakes remain engaged through air pressure, preventing inadvertent application.
Driving Considerations
- Braking power can fade if drastic increases in pedal pressure are required to maintain speed on downgrades.
- To maintain control during emergency stops, brake in a manner that keeps the vehicle traveling in a straight line.
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