#1. How can you tell how much air pressure is in the service reservoirs?
The reservoir pressure gauge is connected to the service reservoir. It shows how much air pressure is in the reservoir. In a dual-circuit system, there will be either two gauges, one for each circuit’s service reservoir, or a single gauge with two needles. The gauges are mounted on the instrument panel so you can monitor reservoir air pressures while you drive.
#2. What does the low air pressure warning device warn you about?
Vehicles with air brakes are equipped with a low air pressure warning device. It will activate a red warning light on the dashboard if air pressure in the primary or secondary air tank has fallen to 414 kPa (60 psi) (although some manufacturers’ systems activate at higher pressures). If this happens, you should brake safely to a stop and repair the problem before the air pressure drops to the point that the service brakes won’t work properly. Note: On older vehicles, a “wig wag” (mechanical arm) may activate instead of a warning light.
#3. How can you make sure that your brakes are properly adjusted?
A key part of brake adjustment is making sure that pushrod stroke is within normal limits. There are two methods for doing this: the pry method and the applied stroke method. With either method, someone must observe pushrod travel directly
#4. Which of the following can impair braking effectiveness?
Air brakes can lose their effectiveness from a variety of causes. If a slack adjuster isn’t properly set, the pushrod stroke of that brake chamber can increase to the point that you have to press the brake pedal farther down to achieve the same amount of braking force. If brake drums overheat from repeated or continuous application of the brakes, the drums will expand away from the brake shoes, reducing braking effectiveness (brake fade). Moisture and oil can collect in the bottoms of the air tanks, forming a corrosive sludge that can pass from the tank into other components of the air brake system, damaging them. In cold weather, water in the air tanks can freeze, and ice in the lines or valves can block the flow of compressed air.
#5. How do you apply the parking brakes?
The yellow button on the dashboard is the parking brake valve control. Pushing this control in allows air pressure to flow to the spring parking brake chambers, causing the spring parking brakes to release. Pulling this control out exhausts the air pressure against the spring parking brake chambers, causing the parking brakes to apply. Instructions are usually imprinted on the button.
#6. Which of the following is not a component of a wedge brake?
#7. 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.
#8. A brake lining that has become contaminated with oil or grease indicates a problem with the
A brake lining that has become contaminated with oil or grease indicates a problem with the wheel. For example, oil can leak from a bad wheel seal. As the wheel spins, some of the leaking oil may be splashed onto the brake lining.
#9. Where are the air brake chambers located?
There is a brake chamber at each brake. The brake chamber converts the pressure of compressed air into mechanical force to operate the brake
#10. Different sizes of brake chamber on the same axle can cause
Mismatched brake chambers on the same axle can cause imbalanced braking: The brakes may not apply at the same moment, or one brake may apply more or less forcefully than another. Your vehicle may be placed out of service if a roadside inspection finds it has mismatched brake chambers on the same axle.
#11. If there is a loss of air to the service brakes in a trailer with a spring brake priority system, how can you brake the trailer to a stop?
Trailers with spring brake priority supply compressed air to the spring brakes (to release them) before the service tank has filled. If there is a loss of air to the trailer service brakes, the spring brakes may remain released while the service brakes fail to work. If this happens, the only way to brake the trailer is to close the trailer supply valve (by pulling out the red dashboard knob) to cause the trailer’s spring brakes to apply automatically.
#12. The trailer air supply valve will close automatically if air pressure in the trailer supply line drops to
The trailer air supply valve will close automatically if air pressure in the trailer supply line drops to between 138 and 310 kPa (20 and 45 psi). The red trailer air supply knob on the dashboard will pop out.
#13. You may be fined as much as _______ for driving a vehicle whose brakes are out of adjustment.
You may be fined as much as $2,000 for driving a vehicle with defective brakes. This includes brakes with excessive brake chamber pushrod stroke.
#14. You’re driving a vehicle equipped with an automatic front-wheel limiting system (ratio valve). If you brake hard during an emergency stop, the air pressure delivered to the front brakes will be approximately _____ of the air pressure to the rear brakes.
The front-brake limiting effect is greatest for brake application pressures below 40 psi (276 kPa). At brake application pressures over 60 psi (414 kPa), there is no limiting effect; the air pressure delivered to the front brakes equals that delivered to the rear brakes.
#15. The purpose of the tractor protection valve is
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.
#16. 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.
#17. Spring parking brakes typically require air pressures of at least _______ to completely release.
A spring parking brake can exert a force of up to 2,000 pounds. A brake chamber with a spring brake has two diaphragms: a service brake diaphragm and a spring brake diaphragm. A common type of brake chamber for drive axles is the Type 30/30, which has a 30-square-inch service brake diaphragm and a 30-square-inch spring brake diaphragm. For 80 psi of pressure, 80 × 30 = 2,400 pounds of force, which will be enough to counteract the force exerted by the spring parking brake.
#18. If the outer layer of an air line is damaged, but the inner tube is still OK, what should you do?
Air line chafing is a common roadside violation. If you’re pulled over for a roadside inspection, you can be cited for brake line chafing. If the chafing continues, the inner tube may be damaged eventually as well.
#19. Cut-in pressure must never be lower than
Air brake system pressure must never be lower than 552 kPa (80 psi). This is an absolute minimum; many manufacturers will set a higher minimum pressure.
#20. Why are drivers required to complete a trip inspection report?
Under Division 37 of the British Columbia Motor Vehicle Act Regulations, every carrier must require each of its drivers to submit a trip inspection report. A driver who fails to do so may be fined.
#21. Which of these vehicles is most likely to be equipped with air brakes?
Air brakes are favored for large commercial vehicles because (a) they can produce large braking forces (typically thousands of pounds of braking force at each wheel); and (b) unlike hydraulic fluid, compressed air can be rapidly and automatically replenished in the event of a slow leak.
#22. 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.
#23. When coupling a tractor to a trailer, how many air lines do you have to connect?
When coupling a tractor to a trailer, you must connect two air lines: the service line (also known as the control line or signal line) and the supply line (also known as the emergency line). The service line (usually coloured blue) controls the trailer service brakes. The supply line (usually coloured red) controls the trailer emergency (spring) brakes and supplies air to the trailer air tanks
#24. 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.
#25. 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.
