AIR SYSTEM PIPING DIAGRAMS Pre-121 Trailer Air SystemsExplore further
2021-10-1u2002·u2002Control or Service Line – The air lines in the trailer air brake system that perform the normal braking of the vehicle from the tractor foot valve or hand valve. Control or service lines are commonly associated with the blue air line function of the air system. Control is a post FMVSS 121 term and service is a pre FMVSS 121 term.
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