Truly are the most frequently used mechanical pressure measuring instruments. Their pressure element is often referred to as a Bourdon tube: The French engineer Eug�ne Bourdon used this functional principle in the center of the 19th century. It is predicated on an elastic spring, a c-shaped, bent tube with an oval cross-section.
The result of pressure on a Bourdon tube
Once the internal space of the Bourdon tube is pressurised, the cross-section is thus altered towards a circular shape. The hoop stresses that are created in this technique raise the radius of the c-shaped tube. Consequently, the finish of the tube moves by around two or three millimetres. This deflection is really a way of measuring the pressure. It is used in a movement, which turns the linear deflection right into a rotary movement and, via a pointer, makes this visible on a scale.
Bourdon tube variants
With the c-shaped bent Bourdon tubes, pressures around 60 bar could be displayed. For higher pressures, helical or spiral-type Bourdon tubes are used. According to the geometry, material and material thickness, pressures around 7,000 bar can be realised. Depending on requirement, the pressure elements are made from copper alloys, stainless steels or special materials such as Monel.
Note
Sizzles on Bourdon tube pressure gauges can be found on the WIKA website.