CDL Air Brake - Commercial Driver's License Air Brakes Pre-Trip Air Brake Inspection Questions and Answers

Question 1

During a static air leakage test on a combination vehicle, what is the maximum permissible pressure drop in one minute after the initial drop?

Accepted Answer

3 psi

Answer

For a combination vehicle, with the engine off and the brakes released, the air pressure should not drop more than 3 psi in one minute after the initial pressure drop. For a single vehicle, the limit is 2 psi.

Question 2

A driver is performing a pre-trip inspection and tests the low air pressure warning device. At what pressure should the warning light and buzzer typically activate?

Accepted Answer

At or above 60 psi

Answer

The low air pressure warning light and buzzer must come on at a pressure of 60 psi or higher (or at the manufacturer's specified level, which is typically at or above 60 psi) to alert the driver of low air pressure in the tanks.

Question 3

When testing the air compressor governor, what are the typical cut-in and cut-out pressures?

Accepted Answer

Cut-in at 100 psi, cut-out at 125 psi

Answer

The air compressor governor is typically set to cut-in (start pumping air) at around 100 psi and cut-out (stop pumping air) at around 125 psi. This ensures the air tanks stay within the proper operating range.

Question 4

A driver applies and holds the foot brake for one minute with the engine off. For a single vehicle, what is the maximum allowable air pressure loss during this applied leakage test?

Accepted Answer

3 psi

Answer

During the applied air pressure test for a single vehicle (like a straight truck or bus), the pressure drop should not exceed 3 psi in one minute after the initial drop. For a combination vehicle, this limit is 4 psi.

Question 5

Which of the following steps is performed to test that the spring brakes will engage automatically?

Accepted Answer

Pump the brake pedal to reduce air pressure until the parking brake valve pops out.

Answer

To check the automatic application of the spring brakes, the driver must fan the brake pedal to lower the air pressure. The parking brake valve (and tractor protection valve on combination vehicles) should pop out between 20 and 45 psi, engaging the spring brakes.

CDL Air Brake - Commercial Driver's License Air Brakes Test Practice Test

CDL Air Brake - Commercial Driver's License Air Brakes Test Practice Test

CDL Air Brake - Commercial Driver's License Air Brakes Pre-Trip Air Brake Inspection Questions and Answers