CDL General Knowledge TestDriving SafelyEasy
A commercial driver is conducting a pre-trip inspection of their vehicle's air brake system. They notice that the air pressure gauge rises from 85 psi to 100 psi in 35 seconds. What does this indicate?
- AThe air compressor is building pressure too slowly, indicating a potential issue.
- BThe air pressure relief valve is stuck open, causing a pressure drop.
- CThe air compressor is functioning properly and within acceptable limits.
- DThe air tanks are over-pressurizing, which is a safety concern.
Show answer & explanationAnswer & explanation
Correct answer: C. The air compressor is functioning properly and within acceptable limits.
The acceptable air pressure build-up rate for a single vehicle with air brakes is from 85 to 100 psi within 45 seconds. Since the vehicle achieved this in 35 seconds, it is functioning properly.
Why the other options are wrong
- A. A build-up rate of 85 to 100 psi in 35 seconds is faster than the minimum requirement, not slower.
- B. A stuck-open relief valve would prevent pressure from building, not allow it to build normally.
- D. The pressure only reached 100 psi, which is within normal operating range, not over-pressurized.
Air Brake Build-Up Rate
The speed at which the air compressor can increase air pressure in the air tanks from a specified low pressure to a specified high pressure.
- Single vehicle: 85 to 100 psi in 45 seconds or less.
- Combination vehicle: 85 to 100 psi in 45 seconds or less.
- Ensures the compressor is capable of maintaining adequate air supply.
Memory trick: Pressure builds, safety ensures.