166. Water meters are used to measure the quantity of water which passes through the service pipe to the building.

Meters should always be set level to secure proper operation of the working parts. They should be placed on the main service pipe, close to the point where it enters the premises, with a waste cock on the side next to the mains, so that the water may be drained from it when desired. An air chamber of generous size should be attached to the service pipe close to the meter, upon the inlet side, to absorb all the shocks that occur in the pipes.

167. The meter must be placed so that the dials can be readily observed. The method of reading the dials is about the same in all kinds of meters. Fig. 61 shows the ordinary arrangement. The figure to be taken is always that one which the pointer has last passed, not the one which it is approaching. The figure which is indicated upon the dial, marked 10, must be put down first; that is, in the units place. ' To the left of it put down the figure indicated upon the dial marked 100; to the left of that put down the figure indicated upon the dial marked 1,000, and so on. Thus, the dials in Fig. 61 indicate 6,417 cubic feet. The small dial, marked one foot, indicates only fractions of a cubic foot. To find the quantity of water which has passed through the meter in any certain time, subtract the previous reading from the later one.

Fig. 61.

Great care must be taken to protect the meter, by means of a fine strainer, from the entrance of fish, sand, etc. The working parts are usually made of hard rubber, which is quickly destroyed by hot water. If there is any danger of hot water flowing back from the boiler to the meter, a meter should be used which has its working parts made of brass or bronze.

The accuracy of a water meter may be tested by weighing the water which passes through it. Several tests should be made, drawing the water slowly in some tests, and as rapidly as possible in others. An ordinary barrel will hold about 5 cubic feet, or between 350 and 400 pounds of water, and is of convenient size for this purpose.

Red or white lead should not be used in screwing up joints in meter connections, or the pipe which joins the meter to the source of water supply, because some of it is liable to reach the interior working parts and clog their movements.

All meters must be carefully protected from frost.