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

Selection

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) and (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 be protected by an appropriate backflow preventer only.

Vacuum breakers should be corrosion-resistant. Backflow pre venters, including accessories, components, and fittings that are 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.

Installation

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 compliance.