The operation of bellows-type and bourdon tube-type pressure detectors is summarized below.
Bellows and Bourdon Tube Pressure Detectors Summary
In a bellows-type detector:
System pressure is applied to the internal volume of a bellows and
mechanical linkage assembly.
As pressure changes, the bellows and linkage assembly move to
cause an electrical signal to be produced or to cause a gauge
pointer to move.
In a bourdon tube-type detector:
System pressure is applied to the inside of a slightly flattened arc-
shaped tube. As pressure increases, the tube tends to restore to its
original round cross-section. This change in cross-section causes
the tube to straighten.
Since the tube is permanently fastened at one end, the tip of the
tube traces a curve that is the result of the change in angular
position with respect to the center. The tip movement can then
be used to position a pointer or to develop an electrical signal.