CDL Airbrakes Practice Test

Question 1

What is the normal operating pressure range for a commercial vehicle air brake system?

Accepted Answer

100–125 psi

Answer

The normal operating pressure range for a commercial vehicle air brake system is 100–125 psi. The compressor cuts out (stops pumping) around 125 psi and cuts back in around 100 psi. If pressure drops below 60 psi, the low air pressure warning activates.

Question 2

If the low air pressure warning activates while driving, what should you do?

Accepted Answer

Stop safely as quickly as possible

Answer

When the low air pressure warning (typically a buzzer and/or light) activates at around 60 psi, you should stop safely as quickly as possible. At pressures below 45 psi, spring brakes will automatically apply. Continuing to drive risks complete brake failure.

Question 3

What does the air pressure governor control in an air brake system?

Accepted Answer

When the air compressor pumps air into the reservoir

Answer

The governor controls when the air compressor pumps air. It cuts out the compressor (stops pumping) when pressure reaches the cut-out level (around 125 psi) and cuts in (starts pumping again) when pressure drops to the cut-in level (around 100 psi), maintaining the correct operating pressure range.

Question 4

What is the purpose of the air dryer in an air brake system?

Accepted Answer

To remove moisture and oil from compressed air before it enters the tanks

Answer

The air dryer removes moisture and oil from compressed air before it enters the air tanks. Moisture in the system can cause corrosion, freeze brake lines in cold weather, and contaminate brake components. Properly dried air extends component life and prevents winter brake freeze-ups.

Question 5

During a pre-trip inspection of air brakes, you apply the parking brake and release the service brake. Air pressure should not drop more than ____ in one minute.

Accepted Answer

2 psi

Answer

For a static leakage test with brakes released (single vehicle), air pressure should not drop more than 2 psi in one minute. With brakes applied, the drop should not exceed 3 psi per minute for a single vehicle or 4 psi for a combination vehicle. Excessive leakage indicates a system fault.

CDL Practice Test

CDL Practice Test

CDL Airbrakes Practice Test