WATER METER, a mechanism by which the quantity of water or any other liquid flow ing through pipes is measured and recorded automatically. They are of three general types — the 'positive,' the 'inferential' and the •pro portional* meters.
Positive meters measure the actual volume of the water, by the action of a piston working in a cylinder which is successively emptied and filled at the completion of each stroke. The cylinder being of known dimensions affords a measure of the quantity of water introduced. The pistons arc either reciprocating or rotary, or of the oscillating or gyrating disc patterns and they may be single or double. When single, a weight or spring produces the return stroke, but in the case of the double arrange ment, the reciprocal action of the two pistons is controlled by the notion of each other, as in the case of a duplex pump. In rotary piston meters, which may also be of the single or double type, the pistons have interlocking faces and rotate in an air-tight chamber. Upon the outer surfaces of the pistons are a series of projections and recesses which correspond to similar shapes on the inner walls of the cylin der. The pressure of the flowing water causes the piston to tarn so that a senes of recesses or chambers in the cylinder are successively filled and discharged from the inlet to the out let of the meter. When oscillating or gyrating discs are employed in the place of pistons, the wobbling motion of the discs alternately empties and fills the cylinder. Inferential meters meas ure the velocity of the flowing water by record ing the revolutions of a turbine or other water wheel attachment, and the quantity is deduced by computation from that record. Proportional meters measure a fractional part of the full flow and arc, therefore, capable of being set on a small by-pass pipe which brandies from and subsequently rejoins the main pipe, but being only approximately accurate their use is limited.
The registering mechanisms consist of a series of gear-wheels and dials. The flow of the water actuates the gear-wheels, and the num ber of revolutions are recorded on the dials. The arrangement of the mechanism converts the number of revolutions into any desired unit of volume, so that the reading of the dials is termed straight and gives the quantity direct. in cubic feet, the unitgenerally adopted, par ticularky in die United States.
The working parts of meters are made light and durable. Serviceability and accuracy are the qualities required, and in their design the support of the water pressure is employed to reduce to a minimum the loss of head, and the wear and tear of the working parts, and al though a high degree of accuracy is not gener ally required, the meters are made sufficiently sensitive to measure the small flows incident to leakage. Hard rubber is generally used for the discs, and also for the rotary pistons of some meters, but where the liquids are hot, or consist of chemical solutions, brass is generally employed. Possible damage due to clogging by
the introduction offish or gravel is prevented by various forms of strainers and sieves, while effect of frost is guarded against by frost cases.
There are several forms of meters which do not come under the general classes already described. Of these the •Venturi,* constructed by Clemens Herschel of New York, in 1886, is the superior and most useful on account of its simplicity and durability. its basic principles— the relation between the reduction of pressure and the increase of velocity of water flowing through a contracted pipe, was discovered by Venturi in 17%. In construction it consists of two conical shaped pipes with their smaller ends joined together by a collar or throat-piece, re sulting in a shape similar to a pipe contracted at one point of its length. By gauging the pres sure of the water at a point just before, and also directly at the point of contraction, and the relation of these pressures to the diameter of the pipe, the volume of the flow is computed. The tubes are usually constructed of cast iron or riveted steel; but they may also be con structed of masonry or wood. The length of the meter varies from 8 to 16 times the diameter of the uncontracted portion, while the diameter of the contraction ranges from one-fourth to one-half of the full diameter of the tube. They are made in sizes varying from two to about 100 inches, with practically no limit to the possible maximum size, but for practical use where meters of diameters less than six inches are re qyired those with moving r= are cheaper. Waste-water meters are emp in connection with waterworks to measure the rate of con sumption per unit of time, instead of the total volume. They consist usually of a disc placed horizontally in a cone-shaped chamber. The disc is lifted or lowered according to the greater or lesser volume of water passing through the pipe in which it is set, and being connected by a wire with counterweight and pencil which follow the movements of the disc, records the nature and amount of those movements on • paper carried by a drum which is revolved by clockwork. The vertical rulings of the record sheet indicate the time intervals, while the hori zontal lines represents the units of volume. Since all the water consumed in a given district must pass through such a meter, by comparing the rates of consumption of the various dis tricts, the causes of abnormal waste are readily determined and localized.
Another form of water meters, more par ticularly known as current meters, are em ployed in hydraulicaeatttg to measure the velocity and volume of flow of the waters in rivers, large aqueducts and sewers. See Cult