Sensors & Actuators

The BOA subsidiary Flexial utilizes the unique properties of metal edge-welded bellows to provide highly versatile, energy transfer sensing, problem solving components. Flexial’s products are on many applications including bellows-assisted sensors, are aboard military aircraft all over the globe, sensing altitude and pressure for fuel control applications.

Technology Features:

  • Pressure
  • Temperature
  • Altitude \ Aneroid
  • Commercial and Military Aircraft
  • Space Applications
  • Downhole, Oil and Gas
  • Vacuum and Semiconductor Processing

Sensor Types

Pressure Transducers compress with increasing external pressure and expand as the pressure drops. This movement can be used to apply mechanical control force.

Differential Pressure sensors reference one pressure to another rather than to the atmosphere.

Aneroid sensors sense pressure changes relative to absolute zero pressure by creating a vacuum on one side of the bellows. Aneroid sensors sense change in barometric pressure to bias or reference a system to absolute pressure, or to sense changes in altitude and introduce corresponding motion and/or force to a system, such as directly operating a valve or opening a parachute.

Sudden Pressure Relays, or Rapid Rise Relays, are used to detect sudden surges in pressure.

Bellows Sensor Functions

Gas Filled bellows can make the sensor sensitive to both external pressure and temperature in vastly different applications, including:

  • Fuel Controls
  • Air Density Controls
  • Passive actuation in a vacuum or pressure chamber

Liquid Filled bellows can function in a number of transducer applications, including:

  • Temperature-Motion transducer
  • Temperature-Force transducer
  • Pressure-Motion transducer
  • Force-Pressure transducer
  • Motion-Motion transducer
  • Force-Force transducer

Design Considerations

Pressure Transducers

Flexial Pressure Transducers

For pressure transducers, typically two small bellows joined with a capillary tube comprise the liquid-filled system, one the sender, the other the receiver. In pressure-motion transduction, the sender converts pressure of the system that surrounds it to displacement of the equilant through the capillary. Flow of the equilant into the receiver bellows is transduced into motion. An example would be a submarine depth gauge where the sender bellows is in seawater, the capillary passes through the hull and the motion of the receiver bellows moves the linkage on a pressure gauge. In pressure-force transduction, there is almost no motion in either bellows. Pressure on the sender produces force from the receiver.

Temperature Transducers

Flexial Temperature Transducers

The higher coefficient of expansion of liquids over metals will cause a liquid-filled metal bellows to expand with increasing temperature and contract conversely. This is akin to an alcohol-filled thermometer, but with a bellows we can drive force or motion. The liquid (the equilant) can be confined strictly to the bellows, or for greater motion, additional equilant can be in a near or remote bulb. In temperature-force transducers, force can be appreciable with larger bellows. For temperature-motion transduction, motion can be linear to less than 0.5% of full scale for low force applications. Flexial builds liquid-filled transducers as small as 0.250 in. (6mm) OD.

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In case of any questions to our portfolio or the design of our products, please do not hesitate to contact one of our specialists:





Flexial is the BOA Group brand for Aerospace applications.

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