A straight truck or bus air brake system should not leak at a rate of more than ___ psi per minute with the engine off and the brakes released.

• A. 2 psi per minute
• B. 4 psi per minute
• C. 3 psi per minute
• D. 1 psi per minute

Answer: (A)

The main idea is to know how much air the system is allowed to lose when it’s not being used, to ensure the brakes will still be reliable after you start the engine. For a straight truck or bus, the system should not leak more than 2 psi per minute with the engine off and the brakes released. This limit keeps the air pressure from dropping too quickly on parked vehicles, so you’ll still have adequate pressure when you need to apply or release the brakes after starting up. If the leak rate were higher, it would indicate a noticeable loss somewhere in the system (valves, hoses, fittings, seals) that could compromise braking performance. Different vehicle configurations have different limits, with higher rates generally allowed for certain combinations, but 2 psi per minute is the standard for straight trucks and buses.