Bourdon Gauge — FRCA Primary MCQ
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Correct answer: D — Increasing internal pressure tends to straighten a curved, flattened tube and moves a pointer through a linkage
Explanation lettering: B = shown as A · D = shown as B · E = shown as C · A = shown as D · C = shown as E
A is correct. A Bourdon gauge contains a flattened hollow tube formed into a curve, spiral or helix. Increasing pressure within the tube makes its cross-section more circular and causes the tube to straighten. Movement of its free end is amplified by mechanical linkage and gearing to move a pointer. A standard open-case gauge indicates gauge pressure relative to atmospheric pressure, not absolute pressure against a sealed vacuum (B). It does not require two independently connected ports or a diaphragm as described in C. It is mechanically powered by the measured pressure and therefore needs no electrical supply (D). Bourdon gauges can measure pressures far above 100 kPa and are used for anaesthetic gas-cylinder pressure measurement, so E is false.
Reference: UK Ministry of Defence, AP3456: The Central Flying School Manual of Flying, Volume 5—Flight Instruments, Chapter 8, paragraph 5, revised 2010. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/857303/Volume_05_Flight_Instruments.pdf