the valve opens, and the loss is made
good.

[Illustration: FIG. 182.--An automatic ball-valve.]

THE WATER-METER.

[Illustration: 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.

In order to follow the working of the meter, we must keep an eye on
Figs. 183 and 184 simultaneously. Water is entering from A, the supply
pipe. It flows through the cock downwards through channel D into the
lower half of the cylinder. The piston rises, driving out the water
above it through C to the delivery pipe B. Just as the piston completes
its stroke the weight, raised by the rack and pinion, topples over, and
strikes the key-arm, which it sends down till stopped by the
buffer-box. The tap is then at right angles to the position shown in
Fig. 184, and water is directed from A down C into the top of the
cylinder, forcing the piston down, while the water admitted below during
the last stroke is forced up the passage D, and out by the outlet B.