Michigan CDL - Air Brakes Practice Exam

What is the maximum leakage rate for a double combination vehicle during an applied leakage test?

1. 4 psi in a minute

2. 2 psi in a minute

3. 6 psi in a minute

4. 8 psi in a minute

The correct answer is: 4 psi in a minute

For a double combination vehicle during an applied leakage test, the maximum allowable leakage rate is 4 psi in a minute. This standard is set to ensure that the air brake system maintains adequate pressure for safe operation. During the applied leakage test, the brakes are applied and held, and the pressure in the system is monitored for any drop. If the pressure drops more than the maximum specified rate, it indicates that there may be a leak somewhere in the system, which can compromise the effectiveness of the brakes and pose a safety risk. By establishing a limit of 4 psi per minute, the guidelines help ensure that any significant leaks are caught during inspection, thereby promoting safer driving conditions and compliance with regulatory requirements. Other values, like 2 psi, 6 psi, and 8 psi, do not align with the standard set for these vehicles. They either indicate too stringent a requirement or too lenient, which would not adequately safeguard against the risks associated with leaking air brake systems.