A Bourdon tube pressure gauge has an elastic tube that is soldered or welded towards one side into a socket. An adjustment of pressure will cause a deflection inside the tube; This can be proportional to your used pressure and is shipped to a rotary gear which has a pointer. https://auto-brake-parts75207.blogs-service.com/62191003/an-unbiased-view-of-precision-pressure-gauge-test-gauge