The type of backflow prevention assembly required is determined by the degree of hazard. In other words, the severity of the actual or potential hazard will dictate what level of protection is necessary to adequately protect the drinking water. Possible health hazard cross-connections require greater protection. A list of assemblies that are acceptable for installation in the City of Lawrence can be found on the USC Foundation for Cross-Connection Control and Hydraulic Research website.
For temporary domestic possible cross-connections, such as a garden hose, a hose bib vacuum breaker is recommended.
Air Gap – An air gap is the most fail-safe prevention of cross-connection and can be used in high or low hazard applications and for continuous use for backsiphonage or backpressure. These are built into all newer sink and bathtub faucet installations. There must be a gap from the vessel overflow rim to the water outlet of twice the diameter of the pipe feeding the vessel or a minimum of one inch of air, whichever is greater.
AVB – An atmospheric vacuum breaker can be used for low or high hazards for non-continuous flow purposes. Usage cannot be more than 12 hours in a 24 hour period. It can have no valves downstream of installation and cannot be subject to backpressure. AVB devices must be installed six inches above the highest point of downstream piping.
DCVA – A double check valve assembly is a mechanical device consisting of two internally loaded soft seated check valves with positive shut-off valves on both upstream and downstream ends, and properly located test ports. A DCVA is suitable for low hazard applications only. It can be used for either backpressure or backsiphonage.
PVB or SVB – A pressure vacuum breaker or spill resistant pressure vacuum breaker can be used for continuous pressure use in high or low hazard situations. The assemblies must be 12 inches above the highest point of downstream piping and have no backpressure.
RPZ – A reduced pressure zone backflow preventer is an assembly of two independently acting soft seated approved check valves together with a hydraulically operated mechanically independent differential pressure relief valve located between the check valves and below the first check valve. This assembly can be used in high or low hazard continuous pressure situations. It cannot be installed in a pit. This assembly is suitable for backpressure or backsiphonage situations.
ASSE 1022 Dual Check with Atmospheric Vent – A non-testable device that can be used under continuous pressure. This can be used on commercial coffee machines and beverage machines carbonated and non-carbonated. The material must be compatible with carbon dioxide gas if used on carbonated beverage machines.
A list of approved backflow assemblies and their installation specifications can be found at the University of Southern California website.