FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsEasy
A technician is explaining to a trainee how the cockpit hydraulic system pressure gauge displays system pressure. The gauge uses a curved, flattened metal tube that tends to straighten as pressure inside it increases, moving a pointer through a gear mechanism. What type of pressure-sensing element is this?
- ABourdon tube
- BAneroid wafer stack
- CVenturi throat
- DBimetallic strip
Show answer & explanationAnswer & explanation
Correct answer: A. Bourdon tube
The Bourdon tube is a curved, flattened tube sealed at one end; as internal pressure rises, the tube tends to straighten, and this motion is transmitted through a gear/link mechanism to move the pointer. It is the most common mechanism used for aircraft hydraulic, oil, and pneumatic pressure gauges.
Why the other options are wrong
- B. Aneroid wafers are used in altimeters and airspeed instruments to sense ambient air pressure changes.
- C. A Venturi produces a pressure drop for airspeed/vacuum instruments, not a direct pressure gauge reading.
- D. Bimetallic strips respond to temperature changes, not pressure, and are used in temperature gauges.
Bourdon Tube Pressure Gauge
A pressure-sensing mechanism using a curved, flattened, sealed tube that straightens proportionally to internal pressure, driving a pointer through a gear sector and pinion linkage.
- Common in hydraulic, oil, and pneumatic pressure gauges
- Tube straightens as pressure increases
- Motion transmitted via linkage/gear sector to pointer
Memory trick: Bourdon tube bends back to tell you the pressure trend