What air pressure must be built before checking the air brake system?

To ensure that the air brake system is functioning correctly, it is essential for the air pressure in the system to reach a specific level before conducting any inspections or tests. The right air pressure, between 100 to 125 psi, is necessary because this range is typically where the system is fully charged and can adequately supply the required air for the brakes to operate effectively. This pressure level allows for the proper engagement of the braking system, helping the driver accurately assess whether the brakes respond appropriately when engaged.

If the air pressure is too low, it can lead to inadequate performance of the brakes, potentially masking issues that need addressing. By aiming for a pressure of at least 100 psi before testing the system, you ensure that the air brake components are ready for a thorough inspection. This systematic approach enhances safety by validating that the necessary conditions are in place for reliable braking action during operation.