Building Design and Construction Handbook - Merritt - Ventech!

WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS 14.11
Tall buildings may be divided into zones, each of which is served by a separate
down-feed system. (The first few stories may be supplied by an up-feed system
under pressure from a public main.) Each zone has at its top its own storage tank,
supplied from its own set of pumps in the basement. All the pumps draw on a
common suction tank in the basement. Also, each zone has at its base its own water
heater and a hot-water circulation system. In effect, the distribution in each zone
is much like that shown in Fig. 14.2.
If space is not available to install storage tanks at the top of each zone, the main
water supply from a roof-mounted storage tank may be supplied to the zones if
pressure-reducing valves are utilized to reduce the supply-water pressure to an acceptable
level at each zone.
14.6.4 Prevention of Backflow
All water-supply and distribution piping must be designed so there is no possibility
of backflow at any time. The minimum code-required air gap (distance between the
fixture outlet and the flood-level rim of the receptacle) should be maintained at all
times. Domestic water systems that are subject to back siphonage or backflow
should be provided with approved vacuum breakers or backflow preventers (Art.
14.3). Before any potable-water piping is put into use, it must be disinfected using
a procedure approved by the local code authorities.
14.6.5 Pipe Materials
Pipes and tubing for water distribution may be made of copper, brass, polyvinyl
chloride (PVC), polybutylene, ductile iron, or galvanized steel, if they are approved
by the local code. When materials for potable-water piping are being selected, care
should be taken to ensure that there is no possibility of chemical action or any
other action that might cause a toxic condition.
14.6.6 Fittings
These are used to change the direction of water flow (because it usually is not
practical to bend pipe in the field), to make connections between pipes, and to plug
openings in pipes or close off the terminal of a pipe. In a water-supply system,
fittings and joints must be capable of containing pressurized water flow. Fittings
should be of comparable pressure rating and of quality equal to that of the pipes
to which they are connected.
Standard fittings are available and generally may be specified by reference to an
American National Standards Institute or a federal specification. Fitting sizes indicate
the diameters of the pipes to which they connect. For threaded fittings, the
location of the thread should be specified: A thread on the outside of a pipe is
called a male thread, whereas an internal thread is known as a female thread.
Ductile-iron pipe is generally available with push-on mechanical joint or flanged
fittings. Brass or bronze fittings for copper or brass pipe also may be flanged or
threaded. Flanges are held together with bolts. In some cases, to make connections
watertight, a gasket may be placed between flanges, whereas in other cases, the
flanges may be machine-faced. Threaded fittings often are made watertight by coating
the threads with an approved pipe compound or by wrapping the threads with
teflon tape before the fittings are screwed onto the pipe.