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Why are two air pressure gauges (or a dual gauge) checked against each other during an inspection?
- A.One gauge is only a spare and should always read zero
- B.The gauges should always show different pressures by a wide margin
- C.Only the higher reading matters for safe driving
- D.Both primary and secondary readings should be present and sensible, showing each part of a split system is building and holding air
Correct answer
D. Both primary and secondary readings should be present and sensible, showing each part of a split system is building and holding air
Why
Dual air systems are a safety backup, and the gauges are how the driver knows both halves are alive. A tank or circuit that does not build pressure removes that backup and must be investigated.
Manual topic: Air Brakes - Brake Inspection · From the Air Brakes practice bank (AB-139).