What is a Bourdon tube and how does it measure pressure?

A Bourdon tube is a curved, flattened metal tube that tends to straighten when internal pressure increases. This mechanical displacement is converted to pointer movement on a dial through a gear mechanism. Bourdon gauges are simple, reliable, and commonly used for local pressure indication in ranges from vacuum to 100,000 psi. C-type (270 degree arc), spiral, and helical designs are used depending on sensitivity requirements.