WATER METERS. 345 WATER METERS. rotary piston meters iiiiiy also Ik' (loublc or single. The double lyjie is niucli lil<e the rotary jnuiiij, two pistons Willi interlocking faces revolving in an air-tigiit clianiber. Some of the single rotary pistons have a series of curved pro- jections and indentations on their outer sur- faces. Corresponding to these are similar va- riations in the cylinder in which the piston revolves. The piston is not fl.ed rigidly at its centre. The incoming water causes the piston to enter and leave successive indentations in the inclosing cylinder. In other words, a series of chambers are successively tilled from the inlet and discharged toward and finally at the outlet of the meter. In place of a piston of this sort a disk or diaphragm is very commonly employed, so constructed as to giye an oscillating or wab- bling motion. In this way the chambers are alternately filled and enijitied. Inferential meters generally have as their primary moving part a series of vanes or liuckets, or else employ a screw. The velocity of the water is indicated liy this means. The Venturi meter generally stands in a class by itself. Its usefulness depends wholly upon the increase in velocity and consequent reduction in pressure caused by contracting the diameter of a pipe through which water is flowing. By measuring the pressures before and directly at the point of contraction, and taking into account the diameter of the pipe, the flow may be com- puted. There are no working parts in the meter itself. The contracted tvibe is composed of two conical-shaped pipes, generally of east iron or riveted steel, with their small, truncated ends joined together with a bronze throat piece. The whole tube might be made of masonry or wood. The total length of the meter is from 8 to 10 times the diameter of the uneontracted portion. The contraction has from one-half to one-fourth the diameter of the full size of the tube. Registering Mechanisms. On all the types of meters described, except the Venturi, which has no working parts, the movements are trans- mitted through cog-wheel mechanisms to a dial or series of dials ; or to what is termed a straight reading register, where the actual quantity passed may be read off at a glance. The mechan- ism is so arranged as to convert the revolu- tions or other movements of the meter into any desired unit of volume. In the United States the unit emploj-ed is generally cubic feet. The regis- tering device of the Venturi meter is described as a calculating mechanism driven by weights which converts differences in pressure into correspond- ing velocities, and thence, for a given size of pipe and for a given period of time, into g.allons. A drum revolved by clockwork provides for the time element. If occasional observations of rates of flow or of volume are sufficient, these may be read from time to time on pressure gauges, or taken off as desired, from self-recording gauges, and rates or total volumes computed therefrom. Waste-Water Meters or District Meters indicate the rate of consumption per unit of time, instead of the aggregate volume. . hori- zontal disk is so placed in a chamber shaped like the frustum of a cone as tn be lifted by the flow of water upward through the chamber. The greater the volume of water passing through the pipe in which the disk is set. the higher the disk ■will be lifted, in order to increase the annular space through which the water must pa.ss. The disk is connected liy means of a wire with a counter- weight and pencil. When the disk rises the weight and pencil fall. The pencil makes a mark on a paper placed on a drum revolved by clockwork. The paper is ruled vertically for elements of time and horizontally for units of volume; thus the device registers the rate of flow. Such meters are so located that all the water of a district must pass through them. By comparing day and night rates of consump- tion of various districts, abnormal conditions nuiy be detected and further steps may be taken to ascertain the cause of the waste. See Water- Works. The meter just described was invented by George F. Deacon, of Liverpool, Kngland, and has been more widely used abroad than in Amer- ica. The Venturi meter may be employed for the same general purpose. It was invented by Clemens Ilerschel. of New York City, about 1886, but the fact that there is a relation between loss of pressure in a contracted tube and the amount of water flowing through it wa.s discovered by Venturi in 17!)(i. One of the earliest water meters in the United States was the double piston meter, invented by Henry R. Worthing- ton, who also introduced the direct-acting steam pump. Numerous other American meters have been developed to a high state of cfTiciency. For sizes from 'o to 4 inches in diameter almost any of the well-known makes of positive or in- ferential meters may be used. Some manufac- turers, however, advise a number of 2-inch meters in place of one of a larger size. Some of the highest grade of piston meters are made in sizes of inches or even higher, and an inferential meter of the screw type has been made up to ■id inches in diameter. Venturi meters from 2 inclies to GO inches in diameter were in use in 1000, and some Qi-2 inches in diameter were then being made. A meter 108 inches in diam- eter was built some years ago for experimental purposes. There is practically no limit to the possible size of Venturi meters, but for diameters of inches or less the meters with moving parts are cheajier. One of the points of superiority claimed for this meter is that it causes less loss of head, or reduction in pressure, than any other type. The durability and simplicity of the Venturi meter is another point in its favor. The working parts of meters are made as light and durable as is consistent with accuracy and serviceability, and they are generally so de- signed to be supported by the water, thus reduc- ing wear and tear and loss of head. Vulcanized rubber is the most common material for the disk and some of the rotary piston meters, but where special strength or power to resist the action of hot water or acids is required, brass or some other composition metal is employed. A variety of devices to protect from damage or clogging are used, including strainers and sieves to keep out gravel and fish, frost cases, and the like. For most purposes a high degree of accuracy of measurement- is not an essential quality in a meter, but it is desirable that meters should be sufliciently sensitive to small flows to detect leakage, which, though minute, may amount to large quantities in the course of time. Positive piston rtieters come to a standstill whenever any- thing prevents their registration. The inferential
