27 questions written from the Pennsylvania Commercial Driver's Manual (PUB 223). Pick an answer to see the rule and the page it comes from.
1. What is the recommended action if a vehicle equipped with automatic slack adjusters is found to be out of adjustment?
Answer: Take the vehicle to a repair facility as soon as possible to have the problem corrected. The handbook advises taking the vehicle to a repair facility rather than manually adjusting the automatic slack adjusters, as manual adjustment may mask underlying mechanical problems.
Pennsylvania Commercial Driver's Manual (PUB 223), page 100: “It is recommended that when brakes equipped with automatic adjusters are found to be out of adjustment, the driver take the vehicle to a repair facility as soon as possible to have the problem corrected.”
2. When should the low air pressure warning light and buzzer activate in a dual air brake system?
Answer: When air pressure drops below 55 psi in either system. The handbook specifies that the warning signal activates when pressure in either the primary or secondary system falls below the 55 psi threshold.
Pennsylvania Commercial Driver's Manual (PUB 223), page 100: “The warning light and buzzer should come on before the air pressure drops below 55 psi in either system.”
3. Why should a driver avoid pushing the brake pedal down when the spring brakes are already engaged?
Answer: The brakes could be damaged by combined forces. Applying the service brake pedal while spring brakes are on creates combined forces that can damage the brake system.
Pennsylvania Commercial Driver's Manual (PUB 223), page 98: “If you do, the brakes could be damaged by the combined forces of the springs and the air pressure.”
4. According to the handbook, what is the primary reason for draining air tanks completely?
Answer: To remove accumulated water and oil that can cause brake failure. The handbook states that water and oil collect in the bottom of the tank and can cause brake failure, particularly if the water freezes.
Pennsylvania Commercial Driver's Manual (PUB 223), page 95: “Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system. For example, the water can freeze in cold weather and cause brake failure.”
5. What action should a driver take if the brakes are very wet in freezing temperatures before applying the parking brakes?
Answer: Use the brakes lightly while driving in a low gear to heat and dry them. The handbook advises heating and drying wet brakes by driving lightly in a low gear to prevent them from freezing.
Pennsylvania Commercial Driver's Manual (PUB 223), page 104: “If the brakes are wet, use the brakes lightly while driving in a low gear to heat and dry them.”
6. In a dual air system, how long should it take for air pressure to build from 85 to 100 psi when the engine is at operating rpms?
Answer: Within 45 seconds. For modern dual air systems, the buildup from 85 to 100 psi must occur within 45 seconds to ensure adequate air supply for braking.
Pennsylvania Commercial Driver's Manual (PUB 223), page 101: “When the engine is at operating rpms, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems.”
7. Why might a driver unnecessarily press and release the brake pedal?
Answer: It causes the air pressure to drop too low for the brakes to work. The handbook explains that unnecessary pedal use releases air faster than the compressor can replenish it, potentially causing brake failure due to low pressure.
Pennsylvania Commercial Driver's Manual (PUB 223), page 96: “Pressing and releasing the pedal unnecessarily can let air out faster than the compressor can replace it. If the pressure gets too low, the brakes will not work.”
8. What action should a driver take if the safety relief valve releases air?
Answer: Have the fault fixed by a mechanic. The handbook instructs drivers to have a mechanic fix the fault if the safety valve releases air, indicating a problem with the system.
Pennsylvania Commercial Driver's Manual (PUB 223), page 96: “If the safety valve releases air, something is wrong. Have the fault fixed by a mechanic.”
9. Why are air storage tanks included in the air brake system?
Answer: To hold enough compressed air to allow brakes to be used several times even if the compressor stops working. The handbook states that the purpose of the tanks is to store sufficient air to permit multiple brake applications in the event of compressor failure.
Pennsylvania Commercial Driver's Manual (PUB 223), page 95: “Air storage tanks are used to hold compressed air. The number and size of air tanks varies among vehicles. The tanks will hold enough air to allow the brakes to be used several times, even if the compressor stops working.”
10. How often should a driver drain air tanks if the vehicle does not have automatic drains?
Answer: At the end of each working day. The handbook specifies draining air tanks at the end of each working day to remove moisture and oil that could cause brake failure.
Pennsylvania Commercial Driver's Manual (PUB 223), page 104: “If your vehicle does not have automatic air tank drains, drain your air tanks at the end of each working day to remove moisture and oil.”
11. When testing the low pressure warning signal, at what minimum pressure level must the signal activate in the air tank?
Answer: Before the pressure drops to less than 55 psi. The warning signal is required to activate before the air pressure falls below 55 psi to ensure the driver is aware of low pressure conditions.
Pennsylvania Commercial Driver's Manual (PUB 223), page 101: “The low air pressure warning signal must come on before the pressure drops to less than 55 psi in the air tank (or tank with the lowest air pressure, in dual air systems).”
12. What does an increasing application pressure gauge reading indicate while trying to hold the same speed?
Answer: The brakes are fading. The handbook defines that needing more pressure to maintain speed is a sign that the brakes are fading.
Pennsylvania Commercial Driver's Manual (PUB 223), page 97: “Increasing application pressure to hold the same speed means the brakes are fading.”
13. When should a driver avoid using the parking brakes immediately after descending a steep grade?
Answer: When the brakes are very hot. The handbook states that using parking brakes when they are very hot can damage them due to the heat.
Pennsylvania Commercial Driver's Manual (PUB 223), page 104: “Do not use the parking brakes if the brakes are very hot (from just having come down a steep grade), or if the brakes are very wet in freezing temperatures.”
14. What is the function of the electric switch in the air brake system regarding other drivers?
Answer: It turns on the brake lights when you put on the air brakes. The handbook states that an electric switch activated by air pressure turns on brake lights to warn drivers behind you.
Pennsylvania Commercial Driver's Manual (PUB 223), page 97: “The switch turns on the brake lights when you put on the air brakes.”
15. According to the handbook, what is the required threshold for the low air pressure warning signal to activate on vehicles with air brakes?
Answer: Before the air pressure falls below 55 psi. The handbook states that the visible warning signal must activate before the tank pressure drops below 55 psi.
Pennsylvania Commercial Driver's Manual (PUB 223), page 97: “A warning signal you can see must come on before the air pressure in the tanks falls below 55 psi.”
16. When braking hard on slippery surfaces in a vehicle without ABS, what is a primary risk to steering control?
Answer: The steering wheels may lock up, causing loss of steering control. Without ABS, hard braking can lock the steering wheels, which directly results in the loss of steering control.
Pennsylvania Commercial Driver's Manual (PUB 223), page 102: “When your steering wheels lock up, you lose steering control.”
17. What is the function of the air compressor governor in an air brake system?
Answer: It controls when the compressor pumps air by stopping it at the cut-out level and starting it at the cut-in pressure. The handbook defines the governor's role as regulating the compressor's operation based on specific pressure thresholds (cut-out and cut-in levels).
Pennsylvania Commercial Driver's Manual (PUB 223), page 95: “The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the "cut-out" level (around 120-140 pounds per-square-inch or "psi"), the governor stops the compressor from pumping air. When the tank pressure falls to the "cut-in" pressure (around 100 psi), the governor allows the compressor to start pumping again.”
18. In newer vehicles with air brakes, how do you apply the parking brakes using the diamond-shaped, yellow, push-pull control knob?
Answer: Pull the knob out. The handbook specifies that pulling the knob out engages the spring brakes, while pushing it in releases them.
Pennsylvania Commercial Driver's Manual (PUB 223), page 98: “You pull the knob out to put the parking brakes (spring brakes) on, and push it in to release them.”
19. According to the handbook, what is the approximate additional distance added by air brake lag at 55 mph on dry pavement?
Answer: About 32 feet. The handbook states that the lag distance adds about 32 feet at this speed.
Pennsylvania Commercial Driver's Manual (PUB 223), page 103: “The air brake lag distance at 55 mph on dry pavement adds about 32 feet.”
20. Which of the following accurately describes the three different braking systems in an air brake setup?
Answer: Service brake, parking brake, and emergency brake. The handbook lists the three components of the air brake system as the service brake, parking brake, and emergency brake.
Pennsylvania Commercial Driver's Manual (PUB 223), page 95: “Air brakes are really three different braking systems, service brake, parking brake, and emergency brake:”
21. During the final air brake check for a single vehicle, what is the maximum allowable air pressure drop in one minute when testing the air leakage rate with the engine off and parking brake released?
Answer: Less than two psi. The handbook specifies that for single vehicles, the air pressure loss must be less than two psi per minute during this specific test.
Pennsylvania Commercial Driver's Manual (PUB 223), page 101: “The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles.”
22. At what air pressure range do spring brakes engage when air pressure drops?
Answer: Between 20 and 45 psi. The handbook specifies the exact psi range in which spring brakes activate.
Pennsylvania Commercial Driver's Manual (PUB 223), page 104: “The spring brakes will come on when the air pressure drops into the range of 20 to 45 psi.”
23. At approximately what pressure should the air compressor stop pumping (cut-out) during the governor check?
Answer: About 120-140 psi. The air governor is designed to stop the compressor from pumping once the pressure reaches the specified range of 120 to 140 psi.
Pennsylvania Commercial Driver's Manual (PUB 223), page 101: “Pumping by the air compressor should start at about 100 psi and stop at about 120-140 psi.”
24. According to the handbook, what is the minimum air pressure that must be built up in both the primary and secondary systems before driving a vehicle with a dual air brake system?
Answer: 100 psi. The handbook states that drivers must wait for the air compressor to reach at least 100 psi in both systems before beginning to drive.
Pennsylvania Commercial Driver's Manual (PUB 223), page 100: “Before driving a vehicle with a dual air system, allow time for the air compressor to build up a minimum of 100 psi pressure in both the primary and secondary systems.”
25. What is the function of the alcohol evaporator in some air brake systems?
Answer: To reduce the risk of ice in air brake valves during cold weather. The handbook states that alcohol evaporators help reduce the risk of ice forming in air brake valves and parts during cold weather.
Pennsylvania Commercial Driver's Manual (PUB 223), page 96: “Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather.”
26. Why is it safer to stop while there is enough air in the tanks to use foot brakes rather than waiting for spring brakes?
Answer: Spring brakes do not work on all axles, causing heavily loaded vehicles to take a long distance to stop. The handbook explains that spring brakes are less effective for stopping heavy loads because they don't engage all axles.
Pennsylvania Commercial Driver's Manual (PUB 223), page 104: “A heavily loaded vehicle will take a long distance to stop because the spring brakes do not work on all axles.”
27. How do spring brakes function when the air pressure is removed from the system?
Answer: Powerful springs put on the brakes. Spring brakes rely on mechanical force from springs to apply braking when air pressure, which normally holds them back, is lost.
Pennsylvania Commercial Driver's Manual (PUB 223), page 97: “When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes.”