Bourdon Tube - McDaniel General Service gauges incorporate phosphor bronze or brass bourdon tubes with precision brass movements for reliable service.  Spiral or helical bourdon tubes are used for pressure ranges from 1,000 psi and above in poly 'B' gauges, and from 800 psi and above in the other general service gauges above 800 psi are of alloy steel.

   The spiral or helical tubes reduce workhardening at elevated pressures by spreading the higher degree of stress over more than 1,000 degrees of coil, thereby minimizing the possibilities of failure.