Backflow prevention device
Encyclopedia
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 code
s.
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.
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
supplies from contamination or pollution.
In water supply
Water supply
Water supply is the provision of water by public utilities, commercial organisations, community endeavours or by individuals, usually via a system of pumps and pipes...
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
Plumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
or building code
Building code
A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...
s.
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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, the Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
(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
Check valve
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
is a common form of backflow prevention. In most cases, the law requires a double check (DC), an Reduced Pressure Principle Device(RP
Reduced pressure zone device
A Reduced Pressure Zone Device is a type of backflow prevention device used to protect water supplies from contamination...
) 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 breakerAtmospheric vacuum breakerAn Atmospheric Vacuum Breaker is a backflow prevention device used in plumbing to prevent backflow of non-potable liquids into the drinking water system. It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon...
(AVB) - Check valveCheck valveA check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
(usually not a legally-approved method of backflow prevention) - Chemigation valveChemigation valveA chemigation valve is an apparatus designed to protect water supplies from agricultural chemicals used during chemigation, the application of chemicals such as fertilizers and pesticides through irrigation water...
(primarily used in agriculture) - Double check valveDouble check valveA double check valve or double check assembly is a backflow prevention device designed to protect water supplies from contamination. It is also a valve used in air brake systems on heavy trucks.Usage in Water Supply:...
, 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 deviceReduced pressure zone deviceA Reduced Pressure Zone Device is a type of backflow prevention device used to protect water supplies from contamination...
(RPZ) - Spill Resistant Pressure vacuum breaker assembly (SPVB)
External links
- 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
- {http://www.watts.com/backflowprevention