Bourdon tube pressure gauges will be the most frequently used mechanical pressure measuring instruments. Their pressure element is frequently known as a Bourdon tube: The French engineer Eug�ne Bourdon made use of this functional principle in the middle of the 19th century. It really is based on an elastic spring, a c-shaped, bent tube with an oval cross-section.
The effect 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 which are created in this process raise the radius of the c-shaped tube. Due to this fact, the end of the tube moves by around several millimetres. This deflection is a way of measuring the pressure. It is used in a movement, which turns the linear deflection into a rotary movement and, via a pointer, makes this visible on a scale.
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With the c-shaped bent Bourdon tubes, pressures around 60 bar can be displayed. For higher pressures, helical or spiral-type Bourdon tubes are used. Depending on geometry, material and material thickness, pressures around 7,000 bar can be realised. Depending on the requirement, the pressure elements are constructed with copper alloys, stainless steels or special materials such as for example Monel.
Note
More info on Bourdon tube pressure gauges are available on the WIKA website.