CDL Air Brakes TestInspecting Air Brake SystemsHard
A driver is performing a pre-trip inspection. The vehicle is equipped with a 'wig-wag' type low air pressure warning device. At what approximate air pressure should this device activate?
- A45 psi
- B85 psi
- C20 psi
- D60 psi
Show answer & explanationAnswer & explanation
Correct answer: D. 60 psi
The 'wig-wag' device, or any low air pressure warning, must activate at or above 60 psi (typically between 55-75 psi) in the air tanks. This warns the driver that air pressure is dropping to a potentially unsafe level before the spring brakes activate.
Why the other options are wrong
- A. 45 psi is too low; the spring brakes might begin to apply at this pressure, but the warning must come earlier.
- B. 85 psi is too high for a low air warning; this is typically a build-up test starting point.
- C. 20 psi is the approximate pressure at which spring brakes are fully applied, which is too late for an initial warning.
Low Air Pressure Warning Activation
The air pressure threshold at which a vehicle's low air warning device must activate to alert the driver of critically low air pressure.
- Must activate at or above 60 psi.
- Typically between 55-75 psi.
- Warns before spring brakes apply (20-45 psi).
- Can be a light, buzzer, or 'wig-wag' flag.
Memory trick: Sixty psi, eyes on the sky, or wig-wag's nigh!