BourdonRohre

BourdonRohre, also known as Bourdonrohre in German, are hollow curved tubes used for measuring pressure. They were invented by Eugène Bourdon in 1849 and remain a foundational element of many mechanical pressure gauges.

The tube is sealed at one end and connected to the pressure source at the other. When internal pressure increases, the cross section expands and the curve tends to straighten. This elastic deformation produces a measurable displacement at the tube’s free end, which is transmitted through a linkage to a pointer or to a transducer.

The most common shapes are C-type, where the tube is a closed, curved bend; and also helical and spiral types, which provide greater movement for higher pressures or compact form factors. In C-type tubes, the fixed end and a freely moving end convert bending into straightening; in helical tubes the coil unwinds slightly, and in spiral tubes the curvature changes.

Materials are chosen for elasticity and corrosion resistance, with brass, phosphor bronze, and stainless steel being common.

Bourdon tubes are robust, inexpensive, and do not require external power, making them suitable for gauges in industrial settings, hydraulic and pneumatic systems, and many process industries. They can measure gauge pressure, absolute pressure with a reference vacuum chamber, or differential pressure in specialized configurations.

Limitations include temperature sensitivity, mechanical hysteresis, and long-term creep if not properly sized. Sensitivity decreases at very high pressures, and high-accuracy applications may use alternative sensing elements or compensation tricks.

Today, Bourdon tubes remain widely used in mechanical gauges and in devices that require a simple, rugged pressure indication.