Bourdon tube pressure gauges 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 made use of this functional principle in the center of the 19th century. Spirit is based on an elastic spring, a c-shaped, bent tube having an oval cross-section.
The effect 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. Consequently, the end of the tube moves by around two or three millimetres. This deflection is a way of measuring the pressure. It is used in 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 up to 60 bar can be displayed. For higher pressures, helical or spiral-type Bourdon tubes are used. Based on the geometry, material and material thickness, pressures up to 7,000 bar can be realised. With regards to the requirement, the pressure elements are constructed with copper alloys, stainless steels or special materials such as Monel.
Note
Further information on Bourdon tube pressure gauges can be found on the WIKA website.