The air loss rate for a straight truck or bus with the engine off and the brakes on should not be more than how much?

The air loss rate for a straight truck or bus with the engine off and the brakes on should not be more than how much?

• A. 1 psi in 1 minute
• B. 3 psi in 1 minute
• C. 3 psi in 5 minutes
• D. 5 psi in 1 minute

Answer: (B)

Air brake systems must hold pressure even when the engine is off, otherwise the brakes could fail to respond when you need them. To check this, you look at how quickly the system’s air pressure leaks away while idle. For a straight truck or bus, the allowable leakage is small: the pressure should not drop more than 3 psi in one minute. If it falls faster than that, there are leaks somewhere in hoses, fittings, valves, or the brake equipment that could lead to insufficient braking power in operation. The other rates don’t match the standard safety limit: they either understate the acceptable leakage, extend the window beyond what the test specifies, or exceed the allowable drop in one minute.

Air brake systems must hold pressure even when the engine is off, otherwise the brakes could fail to respond when you need them. To check this, you look at how quickly the system’s air pressure leaks away while idle. For a straight truck or bus, the allowable leakage is small: the pressure should not drop more than 3 psi in one minute. If it falls faster than that, there are leaks somewhere in hoses, fittings, valves, or the brake equipment that could lead to insufficient braking power in operation. The other rates don’t match the standard safety limit: they either understate the acceptable leakage, extend the window beyond what the test specifies, or exceed the allowable drop in one minute.