Figure 8-6.Simple bellows gauge.
devices have the pressure applied to the outside
of the bellows (fig. 8-6).
Simple Bellows Elements
Bellows elastic elements are made of brass,
phosphor bronze, stainless steel, beryllium-
copper, or other metal suitable for the intended
service of the gauge. Motion of the element
(bellows) is transmitted by suitable linkage and
gears to a dial pointer. Most bellows gauges are
spring-loadedthat is, a spring opposes the
bellows and thus prevents full expansion of the
bellows. Limiting the expansion of the bellows in
this way protects the bellows and prolongs its life.
Because of the elasticity in both the bellows and
the spring in a spring-loaded bellows element, the
relationship between the applied pressure and
bellows movement is linear.
Dual Bellows Indicators
Another type of bellows element is the dual-
bellows element. Figure 8-7 is a schematic diagram
of this indicator. Dual-bellows element pressure
indicators are used throughout the Navy as flow-
measuring, level-indicating, or pressure-indicating
Figure 8-7.Differential pressure sensor dual bellows.