CAPACITY OF METERS 115 



As TO THE- CAPACITY AND RESISTANCE OF METERS 



The importance of the loss of head cannot be overestimated. Upon 

 one hand the consumer usually objects to any appreciable lowering of the 

 efficiency of his service pipe as a water carrier, and on the other hand the 

 water department desires to set as small a meter as possible in order to 

 reduce the expense. With meters showing a small loss of head, it is often 

 possible to set meters of a smaller size than the service pipe, which would not 

 be wise with meters showing a large loss of head. It is economy to put 

 the meter department in the hands of a competent engineer who is posted 

 on the flow of water, and who will not always insist on setting a meter of the 

 same size as the pipe when one much smaller is ample for the work. During 

 the past year a number of places have been found having 4-inch services 

 where a i-inch or if -inch meter was ample to measure all the water used. 

 J. Waldo Smith, Trans. Am. Soc. C.E., 41, 1899, p. 360. 



The most commonly used kinds of meters in the United States 

 are: 



(1) Disc meters, consisting of an oscillating disc in a case 

 moved by the water and communicating the motion which repre- 

 sents a certain volume of water to a gear train which indicates 

 the amount on a dial, and 



(2) Rotary meters, being meters in which an irregular or 

 cylindrical drum rolls in a rotary manner in the interior of a 

 case. 



Other types, used mainly for large services, are 



(3) Compound meters for large sizes are a combination of two 

 meters, a small one to register small flows and a large one to 

 register large flows, with an automatic appliance for shifting the 

 flow from one to the other. 



(4) Inferential meters, consisting of a wheel or other discs 

 moved by the flowing water, by impact and without positive 

 displacement. There are many variations of this type. 



With a great majority of water meters the frictional resistance 

 increases as the square of the quantity passing. In other words, 

 the resistance is always a certain number of times as great as 

 the head that would theoretically produce the velocity of the 

 entering water. 



Water meters are usually arranged to handle satisfactorily 

 all the quantities of water that are likely to pass through a pipe 



