CDL Combination Vehicles TestCombination Vehicle Air BrakesEasy
A driver is performing a pre-trip inspection of a combination vehicle's air brake system. The driver drains the air tanks and then starts the engine to observe the air compressor's operation. Within what maximum time should the air pressure build from 85 psi to 100 psi in a dual air brake system?
- A30 seconds
- B45 seconds
- C15 seconds
- D60 seconds
Show answer & explanationAnswer & explanation
Correct answer: B. 45 seconds
Federal regulations require that the air pressure in a dual air brake system must build from 85 psi to 100 psi within 45 seconds when the engine is at operating RPM.
Why the other options are wrong
- A. 30 seconds is less than the required maximum time for pressure build-up.
- C. 15 seconds is too short a time for this pressure build-up.
- D. 60 seconds is too long a time, indicating a potential issue with the air compressor or system.
Air Pressure Build-Up Test (Dual Air System)
A test to ensure the air compressor can quickly restore system pressure, specifically from 85 psi to 100 psi within 45 seconds for a dual air brake system.
- Performed with the engine at operating RPM.
- Checks compressor efficiency.
- Indicates system health and safety.
Memory trick: Fast air pressure rise keeps your brakes alive.