FREE CDL Air Brakes Questions and Answers
To check the slack adjusters on S Cam brakes, which of the following procedures should you follow?
Pull firmly on each slack adjuster while wearing gloves. Make sure the wheels are chocked and park on flat terrain. To change the slack adjusters, you must release the parking brakes.
What is the normal air pressure in an air brake system that has been fully charged?
125 psi. The air pressure of a fully charged air system is normally 125 psi.
How should the "cut in" and "cut out" pressures on your air compressor governor be checked?
All of the above. Run your engine at a quick idle and keep an eye on the air pressure gauge to see if the air governor cuts out at the manufacturer's recommended pressure (usually about 125 psi) to verify your air compressor governor cut-in and cut-out pressures. The governor should cut in at the manufacturer's recommended pressure (usually about 100 psi), therefore while the engine is idle, you should step on and off the brake to lower tank pressure.
When the engine is off and the brakes are engaged, the air loss rate of a straight truck or bus shouldn't exceed what?
When the engine is off and the brakes are engaged, a straight truck or bus's air loss rate shouldn't exceed 3 PSI in a minute.
Why do hydraulic brakes stop more quickly than air brakes?
The air moves through the lines more slowly. Cars and light trucks with hydraulic brakes operate instantaneously. The extra time (about half a second) needed for the air to get through the lines causes an additional delay when using air brakes.
What are the normal cut-in and cut-out pressures for the governor of an air compressor?
First cut: 100 psi; second cut: 125 psi. The governor prevents the compressor from pumping air when the air tank pressure reaches the cut-out level, which is around 125 psi.
In the event that the air compressor leaks, what mechanism will maintain air in the tanks?
The check valve with a single direction. Positioned between the primary air tanks and the air compressor is the one-way check valve. It restricts air flow to one direction only, preventing the air tanks from being drained by leaks in the air compressor. In the event that the trailer breaks away or has a serious leak, the trailer protection valve's job is to maintain air in the brake system. The initial tank that the air compressor fills with air has a safety release valve fitted. A safety valve, which opens at 150 psi, guards against excessive pressure buildup in the tank and system. Another term for the foot pedal is the treadle valve.
What is brake stab?
Until the wheels lock up, apply and release the brakes; once the wheels roll, apply them again. Applying the brakes as firmly as you can without locking the wheels is known as controlled braking. Both stab braking and controlled braking are efficient braking techniques that maintain a straight path for your car and let you turn if needed.
If your air compressor stops, what will happen?
The air tanks will still have sufficient air pressure to stop. You will still have air pressure in your tanks if your compressor quits, but it won't be able to replenish the air you lose when you apply your brakes.
In a dual air system, how quickly should the air pressure build up?
45 seconds to go from 85 to 100 psi. It should take three minutes for the pressure in a single air system to rise from 50 to 90 psi.
How should one go about testing the air leakage rate correctly?
Release the parking brake and turn off the engine. Using a fully charged air system, you should check for air leaks. In addition to releasing the parking brake and timing the air pressure drop, you should turn off the engine. For single cars, the loss rate should be less than two psi in one minute, and for combination vehicles, it should be less than three psi in one minute.