CDL Practice Test: Video 5 Answers (25 Questions)

Question 1

In a combination vehicle, what should the air pressure loss be with a fully charged air system?

Accepted Answer

Less than 3 psi per minute

Answer

For a combination vehicle (tractor-trailer), the acceptable air pressure loss during a static air brake test is slightly higher than for a single vehicle due to the increased complexity and number of air lines. With a fully charged system and the brakes applied, the pressure loss should not exceed 3 psi per minute. A greater loss indicates potential leaks in the system, which must be repaired for safe operation.

Question 2

What is the proper way to test the air leakage rate?

Accepted Answer

Turn off the engine and release the parking brake

Answer

Turn off the engine and release the parking brake. You should test for air leakage with a fully-charged air system. You should turn off the engine, release the parking brake, and time the air pressure drop. 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.

Question 3

Which of the following is the most common type of foundation brake?

Accepted Answer

S-cam drum brake

Answer

The S-cam drum brake is the most prevalent type of foundation brake found on heavy-duty commercial vehicles. When air pressure is applied, the S-cam rotates, forcing the brake shoes against the inside of the brake drum, creating friction to slow or stop the vehicle. Its robust and reliable design makes it ideal for commercial applications.

Question 4

What type of air do air brakes use?

Accepted Answer

Compressed air

Answer

Air brake systems operate by using compressed air, which is stored in tanks and then released to activate the brake components. An air compressor builds up the pressure, and when the driver presses the brake pedal, this compressed air is directed to the brake chambers, applying force to stop the vehicle.

Question 5

What psi level is the safety relief valve set to open at?

Accepted Answer

150 psi

Answer

The safety relief valve is a crucial safety device in the air brake system, designed to protect the air tanks and other components from excessive pressure. It is typically set to open and release air if the pressure in the system exceeds 150 psi, preventing damage or rupture of the air tanks.