496 



WATER SUPPLY AND SEWAGE DISPOSAL 



pressure is maintained than it does when a low pressure is 

 maintained. 



582. Construction of the Water Meter. There are water 

 meters of many different forms, but most small meters are of 

 the form known as the DISK TYPE. The only moving part in 

 the measuring chamber is a hard rubber disk. This disk is 

 borne, at its center, on a small sphere of the same material. 

 The case of the meter is usually constructed of bronze so that 

 it will not rust or corrode. The measuring chamber is of the 



shape of the central portion of a 

 sphere (Fig. 304). As the water 

 passes through the meter, it causes 

 the disk to move with what is known 

 as NUTATION MOTION (nutation from 

 a Latin word meaning nodding). 

 The center of the rubber sphere is 

 the point about which the disk 

 moves. If we were to place a com- 

 mon wagon wheel upon the ground 

 so that it rests upon its hub and we 

 were then to walk around the wheel 

 stepping upon its tire, we should be 

 giving the wheel a nutation motion. 

 The upper end of the hub would move with a nodding motion 

 as seen from one side. The water flowing through the meter 

 produces just this sort of motion in the disk. The disk at all 

 times divides the measuring chamber into two separate and 

 equal-sized chambers. A certain amount of water passes 

 through the meter for each complete nutation of the disk. 

 Projecting above the disk at its center is a pin which engages 

 a short horizontal lever. As the disk rotates, or rather 

 nutates, this lever is carried around and around. A train of 

 gears transmits this motion to the dials, thus recording the 

 amount of water which flows through the meter. 



683. Water Meters Generally Reliable. A good meter is 

 long lived and usually records the amount of water used fairly 



FIG. 304. The water meter. 

 X-ray illustration. 



