In a dual air brake system with minimum sized air tanks, how many seconds should it take to build from 85 to 100 psi?

• A. 30 seconds
• B. 45 seconds
• C. 60 seconds
• D. 90 seconds

Answer: (B)

This tests how quickly the air system can rebuild pressure after starting the engine. In a dual air brake setup with the smallest allowed tanks, the requirement is to raise the pressure from 85 psi to 100 psi within 45 seconds. This time frame ensures the system can deliver enough braking air promptly after start-up and under normal use, even with minimum storage.

If the build time were shorter, like 30 seconds, the system would be more capable than the minimum standard, but the test is based on the minimum tank size, so 45 seconds is the expected benchmark. If it took longer, such as 60 or 90 seconds, it would indicate the system might not replenish air quickly enough for safe braking in typical conditions.