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What is the job of the tractor protection valve?
- A.It protects the paint on the tractor frame
- B.It boosts trailer pressure above tractor pressure
- C.It locks the fifth wheel to the kingpin
- D.It keeps air in the tractor system if the trailer breaks away or develops a major leak, by closing and letting the driver still stop the tractor
Correct answer
D. It keeps air in the tractor system if the trailer breaks away or develops a major leak, by closing and letting the driver still stop the tractor
Why
Without protection, a separated trailer would drain the tractor through the torn lines and leave both units brakeless. The valve slams that door at roughly the low-pressure range so the tractor keeps a usable reserve.
Manual topic: Air Brakes - Spring Brakes and Parking Brakes · From the Air Brakes practice bank (AB-103).