730 



HYDRAULICS AND ITS APPLICATIONS 



the influence of the weight D, the syphon continuing in action until 

 the tank is emptied. As each tank assumes the position indicated by the 

 dotted lines, it suddenly tilts the guide F over, so that the new liquid to 

 be measured falls into the other tank, when the same operation is 

 repeated. It will thus be seen that both tanks are filled automatically 

 with fresh liquid, while the measured liquid runs away into a reservoir or 

 other receptacle as required. 



The number of times each tank is filled and emptied is registered by 

 the indicator H, which is connected with both tanks. When either tank 

 is in a horizontal position, the guide F rests on the support J, which is of 



saddle form, so that when the 

 tank is in the act of tipping no 

 influence is exercised either by 

 the weight of the guide or by 

 the pressure of the liquid in the 

 guide, or by the resistance of 

 the counter. 



(2) The inferential meter 

 consists simply of a small tur- 

 bine, through which the whole 

 supply is passed, which drives 

 the recording apparatus. The 

 water is not actually measured, 

 but its volume is inferred from 

 the number of revolutions of 

 the turbine runner or fan, 



section on Line oo' wh ich is the onl J moving part. 



FIG. 351. Tylofs Inferential Water Meter. The meter must be calibrated 



by allowing it to pass a known 



volume of water per minute, and has the advantage of being small, light 

 and cheap, and fairly accurate for good speeds of flow. Since, however, 

 there is a limiting velocity of flow, below which the reaction on the 

 runner vanes is insufficient to overcome the friction of the bearings and 

 recording mechanism, it is unsuitable for recording small flows. More- 

 over, the runner tends to keep on rotating for some short time after the 

 flow of water has ceased, and thus to over-record the flow. Where taps 

 are opened and closed frequently, this action, unless guarded against, 

 may lead to the flow registered being largely in excess of that actual! 

 taking place. 



Tylor's Inferential Meter (Fig. 351) is of this type. Here water enters 



t, 



i 



