WATER-FLOW METERS 



265 



is prohibitive, or for testing the accuracy of register instru- 

 ments, the manometer may be advantageously used, and it may 

 be connected with the same pipes 

 that serve to connect the tube 

 with the registering apparatus. 



Manometer. The Venturi 

 Meter Manometer as illustrated 

 in Fig. 145, consists essentially of 

 a U-tube using the same principle 

 as a barometer. The large mer- 

 cury well is connected to the up- 

 stream of the Venturi Meter Tube 

 and the throat of the Venturi 

 Meter Tube is connected to the 

 small vertical glass tube, thus the 

 downward motion of the mercury 

 surface in the mercury well is 

 very slight in comparison with 

 the upward motion of the mer- 

 cury surface in the small glass 

 tube. The slight motion of the 

 large surface is properly corrected 

 in the fixed scales of the instru- 

 ment. The rate of flow corre- 

 sponding to the difference in height 

 of the mercury surfaces is read on 

 the graduated scale. This instru- 

 ment is absolutely accurate, con- 

 taining no moving parts whatever 

 except the mercury iself. 



5. WATER-STAGE REGISTERS 



Automatic water-stage regis- 

 ters are divided into two classes 

 those making a printed record, 

 and those making a graphic record. 



In the first type a printed record of the gauge height and time 

 is made, while in the second type the record is traced by a pen or 

 pencil on the surface of a paper sheet, both moving in harmony 

 with time and height. 



FIG. 145. Barometric Venturi 

 Manometer. 



