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

A 2

With a basically fully-charged air system (within the effective operating range for the compressor), turn off the engine, release all brakes, and let the system settle (air gauge needle stops moving). Time for one minute. The air pressure should not drop more than: 2 psi for single vehicles.