Bourdon tube

Bourdon tube
CEphoto, Uwe Aranas · CC BY-SA 3.0 · source
Name	Bourdon tube
Caption	Schematic of a spring-operated metallic pressure sensing element
Inventor	Eugène Bourdon
Introduced	1849
Used	Pressure measurement in industrial and scientific instruments
Components	Curved metallic tube, linkage, gear train, pointer, casing
Applications	Steam engines, boilers, compressors, hydraulics, pneumatics, HVAC

Bourdon tube is a mechanical pressure-sensing element consisting of a curved, hollow metallic tube that tends to straighten as internal pressure rises, converting fluid pressure into a measurable mechanical displacement. It provides a simple, robust method for indicating pressure in industrial, marine, and laboratory instruments and forms the core of many mechanical gauges and transmitters. Developed in the 19th century, it has influenced instrument design in industries ranging from steam engineering to aerospace.

History

Eugène Bourdon devised the device in 1849 while working amid industrial advances associated with the Industrial Revolution, contemporaneous with developments such as the steam engine, the Great Exhibition, and innovations in metallurgy promoted by institutions like the École Polytechnique. Its adoption paralleled safety debates exemplified by incidents like the Sultana disaster and regulatory responses in the era of the Boiler Act in the United Kingdom and similar legislation elsewhere. Manufacturers in cities such as Paris, London, and Berlin commercialized gauges for firms including early instrument makers that later became part of conglomerates comparable to Siemens and General Electric. The Bourdon tube's dissemination intersected with standards activities that would lead to organizations similar to British Standards Institution and later international bodies such as International Organization for Standardization.

Design and principle of operation

The element is a curved, often C- or spiral-shaped metallic tube sealed at one end; pressure applied to the interior produces hoop stress and an axial strain that tends to straighten the tube. This mechanical motion is transmitted via a linkage and geared sector to a pointer on a dial, a mechanism analogous to linkages used in devices like the Watt governor and kinematic assemblies found in chronometer escapements. Materials such as phosphor bronze, stainless steel, and beryllium copper are selected based on compatibility with media encountered in systems designed by companies like DuPont or suppliers to naval programs like those of the Royal Navy and the United States Navy. Design parameters—mean radius, wall thickness, cross-section (ovate, D-shaped, or circular)—are engineered with methods traceable to continuum mechanics developments linked to figures such as Augustin-Louis Cauchy and constitutive models later formalized by researchers associated with institutions like Massachusetts Institute of Technology and École Normale Supérieure.

Types and variants

Variants address range, sensitivity, and installation constraints. Common forms include C-shaped, spiral, helical, and flat ribbon designs; these correspond to device families used in instrumentation from companies like Wika and Ashcroft. Differential Bourdon elements use paired tubes or opposed ends for measuring pressure differences, paralleling differential arrangements found in Wheatstone bridge configurations in electrical metrology. High-pressure adaptations employ thick-walled, reinforced tubes used in contexts akin to hydraulic systems supplied to firms such as Caterpillar and Siemens Energy. Special materials and coatings allow use with corrosive media handled by chemical producers like BASF or in cryogenic applications developed at laboratories similar to CERN.

Applications

Bourdon tube gauges serve in boilers, compressors, hydraulic systems, process plants, and HVAC installations found in projects by corporations like Bechtel and Fluor Corporation. They are integral to maritime engineering on vessels of navies such as the Royal Navy and the United States Navy and have historical roles aboard steamships showcased at events like the World's Columbian Exposition. Analytical laboratories and calibration facilities associated with organizations like the National Institute of Standards and Technology use them for reference and backup sensing. Aerospace ground-support and manufacturing plants at companies such as Boeing and Airbus utilize pressure gauges for pneumatics and fuel systems, while power plants operated by utilities akin to EDF and Exelon employ them for steam and feedwater monitoring.

Performance and accuracy

Accuracy depends on material properties, manufacturing tolerances, temperature compensation, and mechanical linkage quality; grade classes for mechanical gauges have parallels to accuracy classes standardized by bodies like International Electrotechnical Commission and American Society of Mechanical Engineers. Nonlinearity in displacement vs. pressure is corrected through gearing or calibration procedures used by metrology laboratories affiliated with national metrology institutes such as Physikalisch-Technische Bundesanstalt and NPL. Repeatability and hysteresis relate to yield strength, work hardening, and fatigue life described in texts by engineers from institutions like Stanford University and Imperial College London. For high-precision needs, designers may prefer electronic transducers developed by firms like Honeywell or Emerson that convert the mechanical motion to electrical signals with potentiometric or strain-gauge pickups.

Maintenance and safety

Routine inspection, calibration, and protection from overpressure and mechanical shock are standard practice; safety culture echoes frameworks promoted by agencies such as the Occupational Safety and Health Administration and accident investigations by bodies like the National Transportation Safety Board. Installation best practices draw on standards from the American Petroleum Institute and procedures used in petrochemical plants run by companies like Shell and ExxonMobil. Corrosion protection, seal integrity, and relief devices (spring-loaded or rupture-disc systems regulated under rules akin to the Pressure Equipment Directive) mitigate failure modes. Calibration intervals, traceability, and recordkeeping conform to quality systems modelled on ISO 9001 and laboratory accreditation schemes such as those of ILAC.

Category:Pressure gauges