PRESSURE INDICATOR. 



151 



This instrument was invented by Mr. S. 

 Crosby in 1824, and first applied by Mr. 

 G. Lowe at the works of the Chartered Gas 

 Company. 



Pressure-gauges, as the name implies, are 

 instruments by which the velocity with 

 which the gas flows into the mains is ascer- 

 tained. They are made of glass tubes par- 

 tially filled with coloured water, and fur- 

 nished with graduated scales divided into 

 inches and tenths from a point in the centre 

 of the scale marked zero. 



When no gas is passing into the main to 

 which one of these instruments is attached, 

 the columns of water contained in the tubes 

 are in equilibrium with the external air, and 

 stand at 0. When the gas is admitted, the 

 equilibrium is destroyed ; the gas depresses 

 one column and raises the other, the total 

 variation being the amount of pressure. In 

 Fig. 34. 1 have given a form of gauge which 

 has a very neat appearance ; the glass tubes 

 can be taken out and cleaned, which it is 

 difficult to do when the two tubes are con- 

 nected by a simple bend. The pressure 

 marked in the drawing is thirty tenths or 

 three inches ; each column varying fifteen 

 tenths from the zero point. 



The length of the tubes and the graduated 

 scale will of course depend upon the quantity 

 of pressure desired to be indicated. 



Fig. 34. 





