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Question:
The trailer air supply control on newer vehicles is a red 8-sided knob, which you use to control the tractor protection valve. You push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out (which closes the tractor protection valve) when the air pressure drops into the range of 20 to 45 psi. Tractor protection valve controls or “emergency” valves on older vehicles may not operate automatically. There may be a lever rather than a knob. The “normal” position is used for pulling a trailer. The “emergency” position is used to shut the air off and put on the trailer emergency brakes. [Commercial Driver Handbook]
Comments
Alkam 2126
4 years ago
It a great app to study for your CDL tests
Cbow33
4 years ago
Great app
Livvy2u
4 years ago
Mom