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Air Brake Mock

#1. What is the colour coding that is often used for the supply and service lines to the trailer?

To help ensure correct connection, the supply and service lines to the trailer are often colour coded. The supply line (also known as the emergency line) is coloured red, and the service line (also known as the control line) is coloured blue.

#2. Assuming good traction and constant vehicle weight, if you double your speed, your vehicle's braking distance will be

The kinetic energy of a moving object increases as the square of the object’s speed. A vehicle travelling at 80 km/h has four times the kinetic energy of a vehicle travelling at 40 km/h. Brakes use friction to convert the kinetic energy of a moving vehicle into heat. Thus, if you double your speed, it will take four times as long for your brakes to stop your vehicle.

#3. If you uncouple and park an old, single-circuit trailer, you should do which of the following?

A single-circuit trailer has only one braking circuit. And an old trailer might not have a backup braking system (such as spring brakes) either. Hence, if air pressure is slowly lost in that one braking circuit, the trailer brakes will release and the trailer might roll away. To prevent this, block (chock) the trailer wheels as a precaution.

#4. The tractor protection valve closes to stop the flow of compressed air to

The tractor protection valve is typically located behind the cab. Both the supply (emergency) and service (control) air lines pass through the tractor protection valve on their way to the trailer. (The valve has intake and output ports for each line.) In the event of a severe loss of air pressure in the supply line (perhaps because the trailer separated from the tractor), the tractor protection valve will close to prevent compressed air from leaving the tractor, so the tractor service brakes will still be able to work. It will also let the air out of the trailer supply line, which will activate the trailer emergency brakes to stop the trailer.

#5. Where is the air dryer located?

The supply (“wet”) tank tends to get most of the moisture because moisture condenses there as the hot air from the compressor cools. To help alleviate this situation, the air dryer dries the air from the compressor before it enters the supply tank. Note: Today’s air dryer technology is so effective that a “wet” tank may not be needed anymore. In a modern Air Dryer Integrated System (ADIS), air from the air dryer goes directly into the primary and secondary service (“dry”) tanks.

#6. The "Trucks Stop Here – Check Brakes" sign before a steep downgrade is

Wherever a “Trucks Stop Here – Check Brakes” sign is posted, truck drivers are required to stop in the pullout area and inspect the vehicle’s braking system before proceeding

#7. Which of the following are helpful in reducing heat in the air brake system?

Repeated braking and hard braking can overheat the brakes. Many vehicles have engine brakes, retarders or auxiliary brakes to assist the service brakes in slowing the vehicle, thus reducing the chance of overheating the brakes.

#8. When inspecting the brake drums, you should look for

British Columbia Motor Vehicle Act Regulation 26/58 states, “Brake drums or disks must not have external cracks or substantial cracks on the friction surface that reach an edge of the bore or periphery of the disk or any mechanical damage to the friction surface other than wear.”

#9. When you press the brake pedal, the valve underneath the brake pedal ________ to apply the service brakes.

To enable the driver to apply the service brakes by pressing the brake pedal, a foot (treadle) valve is located underneath the pedal. This valve has two supply (input) ports (one from the primary air tank and one from the secondary air tank), two delivery (output) ports, and an exhaust port. When the driver presses the brake pedal, the foot valve opens the delivery ports, and compressed air leaves the delivery ports to activate the service brakes. When the driver releases the brake pedal, the delivery ports close. The air in the brake chambers and hoses is exhausted to the atmosphere, releasing the service brakes. (Note: In many modern CMVs, only some of that air is exhausted through the foot valve’s exhaust port. Some of it is exhausted through the exhaust ports of other valves.)

#10. When brakes become overheated, they also become

Overheating of the brakes can lead to a loss of braking effectiveness, known as brake fade. Your vehicle may take longer to stop. If brake fade continues to worsen, your service brakes may stop working completely. Brake fade is a particular problem for drum brakes, because excessive heat causes the brake drums to expand away from the brake linings.

#11. Why are there two service tanks in a modern air brake system?

Why are there two service tanks in a modern air brake system?

3%For efficiency

90%For safety

1%For fuel economy

7%For greater stopping power

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Both systems are controlled by the one brake pedal. Typically, the primary system operates the brakes on the front axle (and possibly one rear axle as well), and the secondary system operates the brakes on the rear axles. Even if one system totally fails, the driver will be able to make a controlled stop using only the foot valve on the other system, although maximum braking power will be reduced.

#12. What is brake lag?

When you press on the brake pedal, some type of force must be transmitted to the brakes to make them work. Hydraulic brake systems use brake fluid. Because brake fluid cannot be readily compressed, force is transmitted immediately to each brake when you press the brake pedal. Air brake systems use compressed air to produce the force that applies the brakes at each wheel. When you press the brake pedal, compressed air must flow from one part of the system to another. Unlike brake fluid, air is compressible, resulting in a delay of up to 0.4 seconds from the moment you apply or release the brake pedal to the moment that the brakes respond accordingly.

#13. How do you release DD3 safety actuator brakes?

Unlike with spring brakes, it’s not enough to push in the yellow parking brake knob. To release DD3 safety actuator brakes, you must also press the brake pedal for 3–5 seconds.

#14. If your vehicle is equipped with automatic slack adjusters, why must you fully apply the service brakes regularly?

Automatic slack adjusters adjust themselves to compensate for excessive pushrod stroke. If you only make normal service brake applications of 40 – 50 psi (276 – 345 kPa), the automatic slack adjusters will maintain adjustment only for those shorter strokes, not for long strokes from full brake applications of 100 psi (690 kPa). Therefore, to keep automatic slack adjusters properly adjusted, make full brake applications regularly. For example, try to fully apply the service brakes every time you stop at a red light or stop sign

#15. You're driving a vehicle equipped with air brakes. If the low air pressure warning signal comes on, what should you do?

A low air-pressure warning signal indicates that reservoir air pressures have dropped below 60 psi (414 kPa), which means a serious air brake system safety hazard. Bring your vehicle to a safe stop as soon as possible and try to find the cause of the low pressure. If the air pressure drops much lower, your service brakes may fail completely.

#16. What happens to the foot valve when you press down on the brake pedal?

The brake pedal is attached to a valve underneath it, which is called the brake valve or foot valve. When you press the brake pedal, the foot valve opens, allowing air from the service tanks to flow to the brake chambers. The harder you press the brake pedal, the more the valve opens, sending more air to the brake chambers and causing braking force to increase.

#17. During your brake tests, you find that the brakes are not operating safely. What should you do?

If there is any indication of bad brakes, don’t drive the vehicle any farther. Pull over, park, and secure the vehicle. Report the defect so it can be repaired before the vehicle is driven again

#18. Which of the following is a part of a disc brake?

In a disc brake, a caliper forces two brake pads against the disc (also known as a rotor). The resulting friction slows the wheel.

#19. In which of the following situations should a spring parking brake chamber be caged?

If the spring parking brakes have come on because of a loss of air pressure in the braking system, they may have to be released to tow or repair the vehicle. Without air pressure, the only way to release a spring brake is to manually insert a release bolt into the spring brake chamber to release the spring. This is called “caging” the spring

#20. When brake drums overheat,

Excessive or prolonged braking can cause the brake drums to overheat and expand away from the brake linings. This leads to a loss of braking effectiveness, known as brake fade. Your vehicle may take longer to stop. If the brakes continue fading, they may stop working altogether. If you pull over and stop using the brakes, they may recover after they cool down. However, brake fade that continues for a long period can cause changes to the brake linings that will require service.

#21. If the low air pressure warning activates, you should

The low air pressure warning device will activate when air pressure falls to around 60 psi. This is a sign of something seriously wrong with your brake system. Stop your vehicle immediately and don’t drive it again until the problem has been corrected. At 60 psi, your service brakes still have enough braking power to stop your vehicle safely – but not if air pressure falls much lower.

#22. If the low air pressure warning signal comes on, what should you do?

A low air-pressure warning means there is a serious air brake system safety hazard. Bring your vehicle to a safe stop as soon as possible. If the air pressure drops much lower, your service brakes may fail completely.

#23. What maintains normal pressures in the air brake system?

A typical air compressor can produce air pressures of up to 500 psi (over 3,000 kPa), far higher than required for safe operation of the brake system. Therefore, an air compressor governor is employed to keep tank pressures within a relatively narrow range. When tank pressure rises to the “cut-out” level (typically about 862 kPa or 125 psi), the governor prevents the compressor from pumping more air into the tanks. When the tank pressure falls to the “cut-in” level, the governor allows the compressor to pump air into the tanks again. The cut-in level is typically 138–172 kPa (20–25 psi) below the cut-out level.

#24. What is the purpose of the governor?

A typical air compressor can produce air pressures of up to 500 psi (over 3,000 kPa), far higher than required for safe operation of the brake system. Therefore, an air compressor governor is employed to keep tank pressures within a relatively narrow range. When tank pressure rises to the “cut-out” level (typically about 862 kPa or 125 psi), the governor prevents the compressor from pumping more air into the tanks. When the tank pressure falls to the “cut-in” level, the governor allows the compressor to pump air into the tanks again. The cut-in level is typically 138–172 kPa (20–25 psi) below the cut-out level.

#25. Air pressure must rise _____________ with the engine idling at 600–900 rpm within 2 minutes.

To test the air pressure build-up time, start by reducing the pressure to below 552 kPa (80 psi). If the vehicle has a trailer attached, ensure the trailer supply valve is closed (pulled out). With the engine idling at 600–900 rpm, the air pressure must rise from 587 kPa (85 psi) to 690 kPa (100 psi) within two minutes.
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