Air Brake Mock
#1. The governor cut-in pressure is normally _________ below the cut-out pressure.
Governor cut-in pressure is normally 20–25 psi below the cut-out pressure.
#2. The air-loss rate test can be performed only when
To perform the air-loss rate test, first secure the vehicle and release the spring brakes. Next, ensure that air pressure is within its normal operating range. Now fully apply and hold the brake pedal to keep sending compressed air to the service brakes. Watch your air pressure gauges and see what happens to the service tank air pressures.
#3. 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
#4. Finding a small bit of oil during an inspection is NOT serious if it’s coming from
The air produced by the compressor and delivered to the supply tank usually contains some water vapour and a small amount of oil and carbon particles. This is usually normal and not a cause for concern as long as you drain the air tanks of this material daily. However, to avoid forcing this material into the service tanks, you should drain the supply tank of this material before you drain the service tanks.
#5. Evacuating air from the brake chambers will apply
The spring brakes are held back by air pressure. If air pressure is lost, the spring brakes will kick in.
#6. How can you tell if you have cross-connected the supply line and the service (control) line on a tractor-trailer with air brakes?
If you cross-connect the air lines, supply air will be sent to the service (control) line instead of the trailer air reservoirs. Reservoir air will not be available to release the trailer spring brakes (parking brakes). And when you press the brake pedal, service air won’t flow to the trailer brake chambers or relay valves, so the service brakes won’t work either.
#7. If air is lost in one circuit of a tractor-trailer’s dual-circuit system but the compressor and governor are still working properly,
A dual air brake system has two separate air brake circuits, both controlled by the same set of brake controls. Each circuit has its own air tanks, hoses, lines, etc. The primary circuit typically operates the regular brakes on the rear axle or axles. The secondary circuit operates the regular brakes on the front axle (and possibly one rear axle). If one circuit loses air pressure, the other circuit should still work as long as the compressor and governor are still working properly.
#8. In Canada, antilock braking systems (ABS) have been mandatory on all trucks and buses over 4,560 kg that have been manufactured since
In Canada, antilock braking systems (ABS) have been mandatory on all trucks and buses over 4,560 kg that have been manufactured since April 1, 2000
#9. 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.
#10. Air pressure monitoring gauges are located on the _________ of the vehicle.
The air supply pressure gauge is connected to the service tank. It shows how much air pressure is in the tank. In a dual-circuit system, there will be either two gauges, one for each circuit’s service tank, or a single gauge with two needles. The gauges are mounted on the instrument panel so you can monitor tank air pressures while you drive.
#11. The pushrod stroke occurs when compressed air enters
When compressed air enters a brake chamber, air pressure pushes the pushrod out, which moves the slack adjuster. This causes the brake shoes or pads to make contact with the brake drum or disc.
#12. Normally, who can adjust automatic slack adjusters?
Once properly installed, automatic slack adjusters shouldn’t need manual adjustment. If an automatic slack adjuster strokes beyond the maximum allowed, this usually indicates that there are other brake problems that need to be repaired by a qualified brake service mechanic. Don’t attempt to adjust an automatic slack adjuster except in an emergency in which your brakes have failed on the road
#13. You’re driving a tractor-trailer. If you’re applying a pressure of 30 psi to the trailer brakes with the foot valve, you can apply a greater pressure at the same time by also using
A two-way check valve allows compressed air from two different sources to flow through the same air line. The valve will select the source with the higher pressure. In this case, the foot valve and hand valve are connected to two-way check valves that in turn lead to the tractor protection valve, and from there to the control (service) line. For example, if the foot valve is sending compressed air at 30 psi (207 kPa) and the hand valve is sending compressed air at 40 psi (276 kPa), then compressed air at 40 psi (276 kPa) will be sent out to the trailer brakes.
#14. 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.
#15. 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.
#16. 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.”
#17. If you find a major defect in the air brake system, you should
Under British Columbia Motor Vehicle Act Regulation 26/58, it is an offence to knowingly drive a vehicle with defective brakes.
#18. 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.
#19. During normal driving, what keeps the spring brakes released?
Spring brakes contain powerful springs that are normally held back by air pressure. If the pressure drops too low, the spring brakes will automatically kick in.
#20. What powers the air compressor?
Air compressors are either powered by an engine belt or (as is more often the case these days) gear driven directly from the engine. Thus the air compressor runs whenever the engine is running.
#21. 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.
#22. Polarized gladhands on a tractor
To prevent cross-connection of the supply and service lines, polarized gladhands and polarized trailer couplers are now available. The supply gladhands and couplers are shaped slightly differently from the service gladhands and couplers, making cross-connection impossible. However, polarized gladhands can still be connected to universal (non-polarized) trailer couplers, so cross-connection in this situation is still possible.
#23. The spring brakes will start to apply when the air pressure falls below
If air pressure falls below 414 kPa (60 psi), the spring brakes will begin to apply automatically.
#24. The coil spring in most spring parking brake chambers can exert a force of
The coil spring in most spring parking brake chambers can exert a force of 1,500 – 2,000 pounds (680 – 907 kg). Note that a fully charged and working air brake system can exert forces greater than this to get the spring parking brakes to release.
#25. Under British Columbia law, how often must air brakes be inspected?
Under federal and provincial laws, air brakes must be inspected daily. Do it as part of your pre-trip inspection.
