HOW METERS SLIP 141 



and a meter manufacturer. This reflects the state of the art 

 as it had developed up to that time. It would be interesting 

 if a corresponding up-to-date statement of meter practice could 

 be made by someone as competent to speak as John Thomson 

 was at the time this paper was presented. Unfortunately, no 

 such statement is available. However, many of the underlying 

 principles of meter construction remain the same in 1917 as 

 they were in 1891. 



The type of water meter sold and used in greatest numbers in 

 American cities consists of a hard rubber disc rotating in a bronze 

 casting. This is called the disc meter. In another type called 

 a rotary meter, the rotating member is fluted prism and in 

 outline it fits as it revolves with the openings in the bronze 

 case. In a disc meter water may flow between the edge of 

 the disc and the inside of the bronze casing against which it 

 oscillates. In the rotary meter the moving part rolls or turns 

 upon each part of the outside case in succession and presumably 

 fits tightly upon it, but water may flow between the ends of 

 the moving parts and the bronze faces above and below. In 

 both types the fit between the rubber and the bronze is made 

 to be as close as circumstances permit. It is closer now than 

 it used to be. Years ago when unfiltered river water was 

 used in many American cities, the clearance had to be arranged 

 with reference to the particles of grit. With clear filtered water 

 this clearance can be reduced and the amount of slippage is 

 decreased. The rates of expansion of rubber and bronze with 

 changes of temperature are not the same and some inequalities 

 grow out of this difference. There is bound to be some wear 

 of the moving parts in the course of time and the effect of this 

 wear is to increase the spaces through which water may pass 

 without moving the meter. In large meters the amount of water 

 that will pass before the meter begins to move may be consider- 

 able. 



It is possible to make new meters that will show but little 

 slip, John Thomson stated : * 



* Trans. Am. Soc., C.E., Vol. XLI, p. 354, 1899. 



