Backflow prevention valves
Backflow prevention devices prevent reverse flow of the supply
in a water system. A vacuum breaker prevents back siphonage in
a nonpressure system, while a backflow preventer prevents back
flow in a pressurized system
Vacuum breakers and backflow preventers should be selected on
the basis of the local plumbing codes, the water supply impurities
involved, and the type of cross-connection.
Impurities are classified as (1) contaminants (substances that
could create a health hazard if introduced into potable water)
(2) pollutants (substances that could create objectionable conditions
but not a health hazard).
Cross-connections are classified as nonpressure or pressure
connections. In a nonpressure cross-connection, a potable water
pipe connects or extends below the overflow or rim of a receptacle
at atmospheric pressure. When this type of connection is not protected
by a minimum air gap, it should be protected by an appropriate
vacuum breaker or an appropriate backflow preventer.
In a pressure cross-connection, a potable water pipe is connected
to a closed vessel or a piping system that is above atmospheric
pressure and contains a nonpotable fluid. This connection should
protected by an appropriate backflow preventer only.
Vacuum breakers should be corrosion-resistant. Backflow pre
venters, including accessories, components, and fittings that
2 in. and smaller, should be made of bronze with threaded connections.
Those larger than 2 in. should be made of bronze, galvanized
iron, or fused epoxy-coated iron inside and out, with flanged
connections. All backflow prevention devices should meet applicable
standards of the American National Standards Institute, the Canadian
Standards Association, or the required local authorities.
Vacuum breakers and backflow preventers equipped with atmospheric
vents, or with relief openings, should be installed and
located to prevent any vent or relief opening from being submerged.
They should be installed in the position recommended by the manufacturer.
Backflow preventers may be double check valve (DCV) or re
duced pressure zone (RPZ) types. Refer to manufacturers’
information for specific application recommendations and code