This post is apropos of nothing; it's just something that I happened upon, and I thought I'd share it.
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A Bourdon tube is a device that forms the heart of many pressure measurement gauges. A Bourdon tube is an arced, flattened tube, closed at one end. Gas pressure applied at the tube's open end will tend to 'straighten' the tube slightly. That 'straightening' results in a linear deflection of the tube's closed end. That deflection is linked to an indicating needle movement, and used to indicate the magnitude of the applied gas' pressure.
The linkages and needle movements can be pretty elaborate little mechanisms, but here's an example of what may be the simplest Bourdon tube gauge possible. The face of the gauge looks like this.
The mechanism at the rear of the gauge's face looks like this.
The hole in the white fitting at the centre of the photo is where air enters the tube. As the tube is 'straightened' by air pressure, the closed end of the tube cranks the gauge's needle across the face's scale to indicate pressure magnitude.
That's the simplest execution of the Bourdon tube principle I've ever seen, which makes it an excellent illustration of the principle.
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