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AIR BRAKE CHECK
With the air pressure built up to governor cutoff (120-140 psi), shut off the engine leaving the key in the “on” or “battery charge” position, chock your wheels if necessary, release the parking brake (all vehicles), and the tractor protection valve (combination vehicle) and fully apply the foot brake. Hold the foot brake for one minute. Check the air gauge to see if the air pressure drops more than three pounds in one minute (single vehicle) or four pounds in one minute (combination vehicle).
Begin fanning off the air pressure by rapidly applying and releasing the foot brake. Low air warning devices (buzzer, light, flag) should activate before air pressure drops below 55 psi or level specified by the manufacturer.
Continue to fan off the air pressure. At a range between 20-45 psi on a tractor-trailer combination vehicle (or level specified by the manufacturer), the tractor protection valve and parking brake valve should close (pop out) on other combinations.
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