Bellows gauges

A Bourdon type dial gauge may be used to indicate pressures within the range 20 toiT to 1 toiT with an accuracy of about 3%. A bellows-operated gauge magnifies the movement of a metal bellows by an optical method and indicates pressure difference over the range 50 torr to 10 toiT. Neither bellows gauges nor Bourdon gauges are in common use in laboratory work. 

Other types of these gauges include the twist tube, spiral tube, and helical tube. Diaphragm and bellows gauges are two other types of pressure sensor that were developed later. For more details on Bourdon tube materials and design, refer to Giacobbe and Bounds [1], Goitein [2], and Considine [3]. 

Bellows gauges (Fig. M-16) have a bellows or elastic chamber expanding to actuate the gauge. They are usually used in low-pressure applications with a maximiun reading of about 50 psig. 

Pressure. Most pressure measurements are based on the concept of translating the process pressure into a physical movement of a diaphragm, bellows, or a Bourdon element. For electronic transmission, these basic elements are coupled with an electronic device for transforming a physical movement associated with the element into an electronic signal proportional to the process pressure, eg, a strain gauge or a linear differential variable transformer (LDVT). 

Since the oil pump inlet is at sump (suction) pressure, a pressure gauge on the pump discharge will indicate the total pressure at that point above atmospheric, i.e. suction (gauge) plus pump head. Any detection element for true oil pump pressure must sense both suction and pump outlet pressures and transduce the difference. Oil safety cut-outs have pipe connections to both sides of the oil pump and two internal bellows are opposed to measure the difference. 

More formal inspections also verily the operation of safety and other controls such as low water and fuel cutoffs, level controls, fusible plugs, pressure gauges, water glasses, gage cocks, stop valves, safety/relief valves, and BD valves and lines. Also, FW pumps, flue and damper arrangements, combustion safeguards, name plate specifications, set pressures, boiler connections, floats, mercury switches, bellows, and other components may be inspected. 

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. 

Commercial bellows elements are usually light-gauge [of the order of (0.05 to 0.10 in) thick] and are available in stainless and other alloy steels, copper, and other nonferrous materials. Multi-ply bellows, bellows with external reinforcing rings, and toroidal contour bellows are available for higher pressures. Since bellows elements are ordinarily rated for strain ranges which involve repetitive yielding, predictable... 

The monomer vapor was then fed through rotameter (7). The total pressure in the reactor was controlled with a bellows-sealed vacuum valve (14) and monitored with a Pirani gauge (13). 

Pressure gauges involving spring and bellows, bell-cased mounting, diaphragms, and other devices have also been developed. 

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