Fig. 181.—A screw-down water cock.
Its place has been taken by the screw-down cock. A very common and effective pattern is shown in Fig. 181. The valve V, with a facing of rubber, leather, or some other sufficiently elastic substance, is attached to a pin, C, which projects upwards into the spindle A of the tap. This spindle has a screw thread on it engaging with a collar, B. When the spindle is turned it rises or falls, allowing the valve to leave its seating, V S, or forcing it down on to it. A packing P in the neck of B prevents the passage of water round the spindle. To open or close the tap completely is a matter of several turns, which cannot be made fast enough to produce a "water-hammer" in the pipes by suddenly arresting the flow. The reader will easily understand that if water flowing at the rate of several miles an hour is abruptly checked, the shock to the pipes carrying it must be very severe.
THE BALL-COCK
is used to feed a cistern automatically with water, and prevent the water rising too far in the cistern (Fig. 182). Water enters the cistern through a valve, which is opened and closed by a plug faced with rubber. The lower extremity of the plug is flattened, and has a rectangular hole cut in it. Through this passes a lever, L, attached at one end to a hollow copper sphere, and pivoted at the other on the valve casing. This casing is not quite circular in section, for two slots are cast in the circumference to allow water to pass round the plug freely when the valve is open. The buoyancy of the copper sphere is sufficient to force the plug's face up towards its seating as the valve rises, and to cut off the supply entirely when a certain level has been attained. If water is drawn off, the sphere sinks, the valve opens, and the loss is made good.
Fig. 182.—An automatic ball-valve.
THE WATER-METER.
Fig. 183.
Some consumers pay a sum quarterly for the privilege of a water supply, and the water company allows them to use as much as they require. Others, however, prefer to pay a fixed amount for every thousand gallons used. In such cases, a water-meter is required to record the consumption. We append a sectional diagram of Kennedy's patent water-meter (Fig. 183), very widely used. At the bottom is the measuring cylinder, fitted with a piston, (6), which is made to move perfectly water-tight and free from friction by means of a cylindrical ring of india-rubber, rolling between the body of the piston and the internal surface of the cylinder. The piston rod (25), after passing through a stuffing-box in the cylinder cover, is attached to a rack, (15), which gears with a cog, (13), fixed on a shaft. As the piston moves up and down, this cog is turned first in one direction, then in the other. To this shaft is connected the index mechanism (to the right). The cock-key (24) is so constructed that it can put either end of the measuring cylinder in communication with the supply or delivery pipes, if given a quarter turn ([see Fig. 184]). The weighted lever (14) moves loosely on the pinion shaft through part of a circle. From the pinion project two arms, one on each side of the lever. When the lever has been lifted by one of these past the vertical position, it falls by its own weight on to a buffer-box rest, (18). In doing so, it strikes a projection on the duplex lever (19), which is joined to the cock-key, and gives the latter a quarter turn.