Which gauge component relies on a Bourdon tube to move the needle?

• A. Capillary tube
• B. Piston
• C. Bourdon Tube
• D. Diaphragm

Answer: (C)

The main idea is how pressure gauges convert pressure into movement. A Bourdon tube is a curved metal tube that tends to straighten as pressure inside increases. That unfolding motion at the tube’s end is mechanically linked to the needle, so the pointer moves to show the pressure value. The capillary tube is just a narrow passage for fluid and doesn’t move the needle by itself. A piston uses sliding motion in a cylinder to transfer force, not the Bourdon mechanism. A diaphragm relies on membrane flexing, not the Bourdon tube. So, the element that directly moves the needle in this gauge is the Bourdon tube.