Bourdon-Tube Pressure Gauge

The heart of a dial pressure gauge is the Bourdon tube: a metal tube of oval section bent into a C and sealed at its free end. The greater the pressure, the farther the free tip moves, but only about 0.125–0.25 in (3–6 mm) across the whole range. A geared movement, built much like clockwork, turns that small movement into the sweep of a pointer, usually over 270° of dial. The tube metal must take a spring temper; phosphor bronze is used for most gauges for air, light oil or water, and beryllium copper for high pressure. The tube's wall thickness and the radius of its curve set the pressure range.