Home › CDL Practice Tests › Air Brakes Questions › Question 66
During an inspection, at what point in the fanning test should spring brake knobs be expected to pop out on many vehicles?
- A.At 120 psi, right after cut-out
- B.At 90 psi, before any warning
- C.As pressure falls into roughly the 20 to 45 psi range, well after the low-pressure warning has activated
- D.Only when the driver pulls them by hand at any pressure
Correct answer
C. As pressure falls into roughly the 20 to 45 psi range, well after the low-pressure warning has activated
Why
The test sequence is warning first, then automatic spring application as the last reserve disappears. Seeing that order confirms the fail-safe works the way the driver will need it in a real air loss.
Manual topic: Air Brakes - Safety Valve and Low Pressure Warning · From the Air Brakes practice bank (AB-066).