Bourdon tube pressure gauges will be 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 really is predicated on an elastic spring, a c-shaped, bent tube with an oval cross-section.
The result of pressure on a Bourdon tube
When 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 process increase the radius of the c-shaped tube. Therefore, the finish of the tube moves by around two or three millimetres. This deflection is a measure of the pressure. It is transferred to a movement, which turns the linear deflection right into a rotary movement and, with 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. With respect to the geometry, material and material thickness, pressures up to 7,000 bar could be realised. With regards to the requirement, the pressure elements are made of copper alloys, stainless steels or special materials such as for example Monel.
Note
Secret Agenda on Bourdon tube pressure gauges can be found on the WIKA website.