148 UNDER-REGISTRATION OF METERS 



as the square root of the pressure shown by the manometer. 

 The formula Q = C\/H may be used where H is the pressure on 

 the manometer in inches. The value of C is to be ascertained by 

 making a number of experiments at different rates, reading the 

 manometer and measuring the water collected in a certain time 

 interval in a graduate. After several experiments to ascertain 

 the value of C have been made with consistent results, it will 

 be unnecessary to collect the water from the discharge in the 

 graduate each time, but instead the simple reading of the 

 manometer can be used with a slide rule calculation to show the 

 rate of flow. 



Each orifice will have its own formula and must be rated. 

 The rating once established should be checked periodically, 

 because it may be changed by slight corrosion of the metal or by 

 incrustations upon it due to deposits from the water. This 

 will depend upon the character of the water and also upon the 

 metal. No chances should be taken. The rating can be so 

 rapidly and easily made that it should be repeated often enough 

 to insure accuracy. 



The record of the meter is to be ascertained by taking off 

 the top so that the spindle can be seen. These spindles revolve 

 with comparative rapidity. For instance, in a certain domestic 

 meter in common use, the spindle makes 433 turns for each 

 cubic foot of water passed, or 58 turns per gallon. If the meter 

 indicates a discharge of 100 gallons per twenty-four hours, 

 the spindle will turn once in fifteen seconds. The time of revo- 

 lution may be taken with a stop-watch if the revolution is slow. 

 Better, the time of several revolutions may be taken, and in 

 case the velocity is greater, the number of revolutions in one 

 minute or some other interval of time may be counted. The 

 number of turns to a gallon for each type of meter can be ascer- 

 tained from the manufacturer, or it can be ascertained by an 

 examination of the gear train, counting the several teeth and 

 making the appropriate calculation. 



In making a test a meter would be connected up in the 

 apparatus, the shut-off gate opened far enough to furnish as much 

 water as needed (deficiency will be indicated by less than full 



