HYDRAULIC GAUGES.
The Piezometer, or pressure gauge, is an instrument for measuring the pressure of water in a pipe.
Fig. 107.
It may be broadly stated that all pressures and weights relating to water, steam, gases, etc., are now recorded by gauges.
The principle of construction of the dial gauge is that the pressure may be indicated by means of a spring and pointer upon a divided dial similar to a clock face, but marked in divisions, indicating pounds, hundreds, etc., pressure instead of hours and minutes. The more approved forms of gauges are now constructed upon the principle of the Bourdon spring or metallic barometer invented in 1849. [(See page 113 for illus.)]
Fig. 108.
The essential principle—or discovery—is this: that a metal curved tube—oval cross section, under pressure, tends to straighten itself according to the force exerted by the pressure inside. Figs. 107 and 108 show the ordinary style of gauge which consists of an elliptical tube, connected at one end to a pipe in communication with the pressure, and at the other end with toothed arc and pinion to a pointer spindle as shown in cuts.