Commercial Driving Air Brakes 2

Question 1

What is the purpose of drain valves on air brake tanks?

Accepted Answer

To remove accumulated water and oil from the air tanks that could cause brake failure

Answer

Air compressors introduce moisture and oil into the air tanks. Draining these contaminants prevents corrosion, ice formation in cold weather, and degraded brake performance.

Question 2

How should you test the low air pressure warning?

Accepted Answer

With the engine off, pump the brake pedal to reduce pressure and verify the warning activates before 60 PSI

Answer

With the engine off, repeatedly pressing the brake pedal reduces air pressure. The warning light and/or buzzer should activate before pressure drops below 60 PSI.

Question 3

What is a slack adjuster?

Accepted Answer

A lever mechanism that adjusts the distance between the brake shoes and drum to compensate for wear

Answer

Slack adjusters connect the pushrod to the brake camshaft and compensate for brake lining wear, keeping the brake adjustment within proper operating limits.

Question 4

What is the air brake applied pressure test procedure?

Accepted Answer

Build pressure to operating level, turn off engine, apply the brake, and observe pressure drop — it should not exceed 3 PSI in one minute for single vehicles

Answer

With full pressure and the engine off, applying the brake and monitoring pressure drop identifies air leaks in the service brake system. More than 3 PSI drop per minute for single vehicles indicates excessive leakage.

Question 5

What is the function of the relay valve in an air brake system?

Accepted Answer

To speed up brake application and release on trailers by using local air supply near the brakes

Answer

Relay valves reduce brake lag on trailers by allowing air to flow from a local tank near the brakes rather than traveling all the way from the tractor, speeding up application and release.

Commercial Driving Practice Test

Commercial Driving Practice Test

Commercial Driving Air Brakes 2