Air Brake Mock
#1. What colour is the parking brake control button?
On the dashboard, the parking brake control is a diamond-shaped, yellow, push-pull button. The trailer air supply control is an eight-sided, red, push-pull button.
#2. Who is ultimately responsible for the condition of the brakes on a vehicle?
As the driver, you are required to conduct a pre-trip inspection before driving the vehicle on the road. This includes a full check of the braking system. You must not drive the vehicle if you find problems with the brakes. You may be fined as much as $2,000 for driving a vehicle with defective brakes.
#3. To “tug test” the trailer service brakes after you couple your tractor to the trailer, you should apply
After coupling your tractor to the trailer, use the hand control valve to test the action of the trailer service brakes. This valve applies only the trailer service brakes, not the tractor service brakes. First, release the entire vehicle’s parking brakes. Next, slowly pull away and use the hand control valve to apply the trailer brakes to check their operation.
#4. How should you test your vehicle's low air pressure warning signal?
Start the test with the pressure above 621 kPa (90 psi) and the ignition on. Then repeatedly press and release the brake pedal. In most vehicles, the low air pressure warning signal should come on when the pressure falls below 414 kPa (60 psi). If the warning device fails to activate at 414 kPa (60 psi), the low air pressure warning device is defective. You should never need to get down to 207 kPa (30 psi).
#5. After you've connected your tractor to a trailer, you should test the trailer service brakes by applying
After connecting your tractor to the trailer, test the action of the trailer service brakes by applying the hand control valve. This valve applies only the trailer service brakes, not the tractor service brakes. For this reason, the trailer hand valve should not be used for normal braking once your vehicle is on the road.
#6. Which of the following is an advantage of wedge brakes over S-cam drum brakes?
In a wedge braking system, the brake chamber directly faces the brake drum. Compared with S-cam drum brakes, wedge brakes lack the exposed linkage of the pushrod, clevis pin and external slack adjuster. (Most wedge brakes have internal automatic adjusters.) Today, most commercial vehicles have disc brakes or S-cam drum brakes. However, wedge brakes are still favored for some military and other applications for which the lack of exposed linkage is advantageous on rough, corrosive, or dangerous ground.
#7. Brake chambers are found on
Each brake is activated by a brake chamber.
#8. Assuming good traction and constant vehicle speed, if you double your vehicle's weight, the braking power to stop your vehicle in the same distance will be
The kinetic energy of a moving object is directly proportional to the object’s weight. A vehicle that is twice as heavy has twice the kinetic energy. Brakes use friction to convert the kinetic energy of a moving vehicle into heat. Thus, if you double your vehicle’s weight, it will take twice as much braking power to stop your vehicle in the same distance.
#9. What are the main components of a simple, basic air brake system?
The necessary components of the simplest possible air brake system are as follows: (a) a compressor to pump air; (b) a governor to control the compressor; (c) air lines to allow the pressurized air to flow between the air brake system components; (d) a reservoir to store the compressed air; (e) a foot valve that sends compressed air from the reservoir to the brakes when you press the brake pedal; and (f) the foundation brakes, one at each wheel.
#10. When should you adjust an automatic slack adjuster?
Once properly installed, automatic slack adjusters shouldn’t need manual adjustment. If an automatic slack adjuster strokes beyond the maximum allowed, it usually indicates that there are other brake problems that need to be repaired by a qualified brake service mechanic.
#11. Compressed air exhaust is
The compressed air that is used in air brake systems can be hazardous if you get near it when it is being exhausted from the vehicle. Compressed air leaving the vehicle travels at a very high speed and carries moisture, oil, dirt and dust. To avoid exposing yourself to it, learn about all the places where the compressed air can be exhausted from your vehicle (such as the exhaust ports of brake valves).
#12. When you drain the air tanks, which tank should you drain first?
Always drain the supply (“wet”) tank first to prevent accumulated moisture in the supply tank from passing farther into the system
#13. Which tank is likely to collect the most moisture?
Hot compressed air from the air compressor goes first to the supply tank. It’s also called a “wet” tank because as the compressed air cools, moisture tends to condense in the tank. When air leaves the supply tank, it splits into two circuits, passing into the primary and secondary air tanks. These tanks are also called “dry” tanks because they collect less moisture than the supply or “wet” tank.
#14. Before beginning the air-loss tests of the air braking system, make sure that the air pressure has risen to at least
According to the British Columbia Driving Commercial Vehicles Handbook, before beginning the air-loss tests, build air pressure back to 100 psi. Then proceed with the air-loss tests.
#15. An S-cam is found in
An S-cam is part of a drum brake in large commercial vehicles. As the S-cam rotates, it forces the brake shoes away from one another and presses them against the inside of the brake drum.
#16. Brake fade can lead to
If the conditions that are causing service brake fade (loss of braking effectiveness) are not corrected, the brakes may continue fading until they can’t slow your vehicle at all.
#17. As part of your pre-trip inspection of a combination vehicle with air brakes and one trailer, you should make sure that the air-loss rate per minute is not greater than
In British Columbia, the maximum acceptable leakage rates per minute are 28 kPa (4 psi) for single vehicles (buses, straight trucks and bobtail tractors) and tractor-trailers with one trailer, and 41 kPa (6 psi) for tractor-trailers with two trailers. If the leakage rate is higher, check for leaks and correct them.
#18. 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.
#19. Maximum governor cut-out pressure is
Governor cut-out pressure should be set somewhere in the range 724–931 kPa (105–135 psi). Usually, it’s 125 psi (862 kPa).
#20. What is the "cut-in" level?
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 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.
#21. A tractor-trailer with one trailer will fail the air-loss rate test if the loss rate exceeds
In British Columbia, the maximum acceptable leakage rates per minute are 28 kPa (4 psi) for single vehicles (buses, straight trucks and bobtail tractors) and tractor-trailers with one trailer, and 41 kPa (6 psi) for tractor-trailers with two trailers. If the leakage rate is higher, check for leaks and correct them.
#22. Which of the following is most likely to have air brakes?
In British Columbia, most large commercial vehicles are equipped with an air brake system.
#23. What are the service brakes used for?
When you press the brake pedal in normal driving, it’s the service brake system that applies the brakes.
#24. How can you make sure that each air tank is securely attached to the vehicle?
To check that each air tank is securely mounted, look at it to see whether it’s loose, and then pull on it to see whether you can pull it loose. Also check the security of the mounting brackets and hardware that hold the air tank to the vehicle
#25. Compressed air entering the brake chambers applies
When you press the brake pedal, compressed air enters the brake chambers and activates the service brakes