Backflow prevention device
A backflow prevention assembly is used to protect water supplies from contamination or pollution.
In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower etc. When pressure fails or is reduced as may happen if a water main bursts, pipes freeze or there is unexpectedly high demand on the water system, the pressure in the pipe may be reduced and may allow contaminated water from the ground, from storage or from other sources to be drawn into the system.
Back pressure is another way that an undesirable contaminant may enter your potable water piping. Sources of back pressure may be pumps in the water distribution system, boilers or heat exchanging equipment and even power washing equipment. In these cases you may have an almost constant risk of overcoming the static water pressure in the piping and when chemicals are used, as they are for commercial/industrial descaling (boilers) or residentially as in deck/siding cleaning such as bleaches (power washing), you would benefit greatly from having a backflow preventer.
To prevent such an occurrence, many regulatory regimes require there to be an air gap or mechanical backflow prevention assembly between the delivery point of mains water and local storage or use  Where submerged mains inflow is permitted a backflow prevention assembly is required. In this way the backflow prevention assembly protects the potable water system from contamination hazards which can be severe. There are over 10,000 reported cases of backflow contamination each year. Some cases can be fatal.
In many countries where regulations allow for the possibility of backflow, approved backflow prevention assemblies are required by law and must be installed in accordance with plumbing or building codes.
A typical backflow assembly has test cocks and shut-off valves and must be tested each year, if relocated or repaired, and when installed.
In the United States, the Environmental Protection Agency (EPA) holds local water suppliers responsible for maintaining a certain amount of purity in potable water systems. Many states and/or local municipalities require annual testing of backflow prevention assemblies. A check valve is a common form of backflow prevention. In most cases, the law requires a double check (DC), an Reduced Pressure Principle Device(RP) device or an air gap when backflow prevention is mandated.
The simplest, and most effective way to provide backflow prevention is to provide an air gap. An air gap is simply a space between any device that opens to a plumbing system (like a valve or faucet) and any place where water can collect or pool.
Partial list of backflow prevention devices
- Air gap
- Atmospheric vacuum breaker (AVB)
- Check valve (usually not a legally-approved method of backflow prevention)
- Chemigation valve (primarily used in agriculture)
- Double check valve, or double check valve assembly (DCVA)
- Dual check valve (non-testable)
- Pressure vacuum breaker assembly (PVB)
- Reduced Pressure Principle Valve (RPPV or RP Device)
- Reduced pressure zone device (RPZ)
- Spill Resistant Pressure vacuum breaker assembly (SPVB)
- ^ "The Water Supply (Water Fittings) Regulations 1999". http://www.opsi.gov.uk/si/si1999/99114802.htm. Retrieved July 26, 2010.
- International Association of Plumbing and Mechanical Officials
- Drinking Water & Backflow Prevention magazine
- International Code Council
- American Society of Sanitary Engineering
- The American Backflow Prevention Association
- Foundation for Cross-Connection Control and Hydraulic Research
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