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How do you test the tractor protection valve during an inspection?
- A.Drive with the trailer supply pulled out and note the stopping distance
- B.Disconnect both glad hands at highway speed
- C.Hold the trailer supply in by hand while draining all tanks
- D.Charge the system, shut the engine off, and fan the brakes to lower pressure; the trailer supply control should pop out as pressure enters its closing range
Correct answer
D. Charge the system, shut the engine off, and fan the brakes to lower pressure; the trailer supply control should pop out as pressure enters its closing range
Why
Fanning the system down in a parked test proves the valve responds to falling trailer supply pressure. If the control never pops or closes far too late, the tractor could lose its air reserve in a real trailer failure.
Manual topic: Air Brakes - Tractor Protection Valve · From the Air Brakes practice bank (AB-234).