Water Meter, an apparatus for measuring the water which flows through a conduit. An approximation may be arrived at by measuring the velocity of water passing through a pipe of a given section. A rotary apparatus in which two S-shaped arms play into each other within a circular box, against the inside of which one end or the other of each of the arms constantly rests, as in Payton's meter, is used by the London water meter company. But the most usual form of meter employs a tilting double pan, or a tilting double-chambered vessel. - Cochrane's meter, exhibited in the United States section of the Paris exhibition of 1867, possesses nearly all the elements of a good instrument. It is represented in section in the figure. The water enters through the pipe p into the chamber a a, which has a dome-shaped air chamber c at the top. From a a the water passes through the tube b into the double pan e e', divided into two equal compartments by a partition. This pan tilts with a rolling friction upon its bearings. Beneath it is a lever, f f', slightly bent, the motion of which is limited by the piece g below it. Suppose the pan e e' to be in the position represented in the figure, the water will flow into the compartment e' through the tube d.

When it contains a certain volume of water the side e' will preponderate. In falling, water will continue to flow into it until the partition passes the tube 5, when it will flow into the compartment e; but the side e' will continue to descend until it strikes the lever f' and causes this to descend to the surface of g. As soon as the side e in turn contains a certain quantity of water, it will descend and discharge itself, as shown in the figure. The rod j, moved up and down by the lever f f', operates a lever n o g, which by means of a ratchet movement registers the number of vibrations on dial plates in a case r, at the same time alternately opening and shutting orifices in the box l m, which allow of the exit of a small quantity of water and the admission of air into the chamber d. The water is discharged through the stopcock i, or by pipes. - Another form of tilting meter is that of E. Dnboys of Paris. It consists of two basin-shaped vessels with thin rims applied so as to enclose a cavity. A flexible diaphragm of caoutchouc is held between the rims, dividing the cavity in two. Passing transversely through the axis of the double vessel there is a rod, having around it a sliding weight which is attached to the centre of the diaphragm.

The water enters alternately through two ducts on either side of the diaphragm, which is thus forced alternately to the bottom of each basin. As each side is in turn filled, the vessel tilts over, and the current of the water is reversed; what was an entrance becomes an exit duct, and what was an exit becomes an entrance duct. The rod holding the weight attached to the centre of the diaphragm has also a limited motion, and is so adjusted that the vessel is kept from tilting until each side is quite filled, by which means accuracy of measurement is secured.