HOUSEHOLD WATER-SUPPLY FITTINGS.

Among these, the most used is the tap, or cock. When a house is served
by the town or district water supply, the fitting of proper taps on all
pipes connected with the supply is stipulated for by the water-works
authorities. The old-fashioned "plug" tap is unsuitable for controlling
high-pressure water on account of the suddenness with which it checks
the flow. Lest the reader should have doubts as to the nature of a plug
tap, we may add that it has a tapering cone of metal working in a
tapering socket. On the cone being turned till a hole through it is
brought into line with the channel of the tap, water passes. A quarter
turn closes the tap.

[Illustration: 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,