Figure 8-6.—Simple bellows gauge.devices have the pressure applied to the outsideof the bellows (fig. 8-6).Simple Bellows ElementsBellows elastic elements are made of brass,phosphor bronze, stainless steel, beryllium-copper, or other metal suitable for the intendedservice of the gauge. Motion of the element(bellows) is transmitted by suitable linkage andgears to a dial pointer. Most bellows gauges arespring-loaded—that is, a spring opposes thebellows and thus prevents full expansion of thebellows. Limiting the expansion of the bellows inthis way protects the bellows and prolongs its life.Because of the elasticity in both the bellows andthe spring in a spring-loaded bellows element, therelationship between the applied pressure andbellows movement is linear.Dual Bellows IndicatorsAnother type of bellows element is the dual-bellows element. Figure 8-7 is a schematic diagramof this indicator. Dual-bellows element pressureindicators are used throughout the Navy as flow-measuring, level-indicating, or pressure-indicatingdevices.Figure 8-7.–Differential pressure sensor dual bellows.8-4
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