Air gap
Encyclopedia
An air gap, as it relates to the plumbing
trade, is the unobstructed vertical
space between the water outlet and the flood level of a fixture
.
A simple example is the space between a wall mounted faucet and the sink
rim (this space is the air gap). Water can easily flow from the faucet into the sink, but there is no way that water can flow from the sink into the faucet without modifying the system. This arrangement will prevent any contaminants in the sink from flowing into the potable water system by siphon
age and is the least expensive form of backflow prevention
.
To further illustrate the air gap, consider what could happen if the air gap were eliminated by attaching a hose
to the faucet and lowering the hose into a sink full of contaminated water. Under the right conditions (if the water supply loses pressure and the sink is higher than the point at which the water supply enters the house, for instance), the dirty water in the sink will be siphoned into the water pipes through the hose and faucet. The dirty water then will be dispersed throughout the drinking water
system.
All plumbing codes require backflow
prevention in several ways. The plumbing fixture manufacturers build the fixtures to meet these codes. A plumber
must not build cross-connections in his daily work practices, and Plumbing Inspectors look for improper designs or connections of piping and plumbing fixtures. A common misconception is that a "high loop" (routing a drain line above a sink's flood level, for instance) will provide the same function as an air gap; this is not true, because the continuous connection in such a case still will allow backflow through siphoning.
An air gap must meet the requirements of being two times the effective inner diameter of the pipe (2*D) in order to be sufficient.
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...
trade, is the unobstructed vertical
Vertical direction
In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
space between the water outlet and the flood level of a fixture
Plumbing fixture
A plumbing fixture is an exchangeable device which can be connected to an existing plumbing system to deliver and drain away water but which is also configured to enable a particular use.-Common fixtures:The most common plumbing fixtures are:*Bathtubs...
.
A simple example is the space between a wall mounted faucet and the sink
Sink
A sink is a bowl-shaped plumbing fixture used for washing hands, for dishwashing or other purposes. Sinks generally have taps that supply hot and cold water and may include a spray feature to be used for faster rinsing...
rim (this space is the air gap). Water can easily flow from the faucet into the sink, but there is no way that water can flow from the sink into the faucet without modifying the system. This arrangement will prevent any contaminants in the sink from flowing into the potable water system by siphon
Siphon
The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...
age and is the least expensive form of backflow prevention
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...
.
To further illustrate the air gap, consider what could happen if the air gap were eliminated by attaching a hose
Hose (tubing)
A hose is a hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes , or more generally tubing...
to the faucet and lowering the hose into a sink full of contaminated water. Under the right conditions (if the water supply loses pressure and the sink is higher than the point at which the water supply enters the house, for instance), the dirty water in the sink will be siphoned into the water pipes through the hose and faucet. The dirty water then will be dispersed throughout the drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
system.
All plumbing codes require backflow
Backflow (plumbing)
Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. It can be a serious health risk for the contamination of potable water supplies with foul water. In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl...
prevention in several ways. The plumbing fixture manufacturers build the fixtures to meet these codes. A plumber
Plumber
A plumber is a tradesperson who specializes in installing and maintaining systems used for potable water, sewage, and drainage in plumbing systems. The term dates from ancient times, and is related to the Latin word for lead, "plumbum." A person engaged in fixing metaphorical "leaks" may also be...
must not build cross-connections in his daily work practices, and Plumbing Inspectors look for improper designs or connections of piping and plumbing fixtures. A common misconception is that a "high loop" (routing a drain line above a sink's flood level, for instance) will provide the same function as an air gap; this is not true, because the continuous connection in such a case still will allow backflow through siphoning.
An air gap must meet the requirements of being two times the effective inner diameter of the pipe (2*D) in order to be sufficient.
See also
- Hydrostatic loopHydrostatic loopA hydrostatic loop, though not often used in plumbing practice, is an arrangement of pipes formed into a vertical loop to prevent backflow of water within the plumbing potable water system. Since a siphon has a maximum height that it can work , a hydrostatic loop is built higher than 33 feet...
- Pressure vacuum breakerPressure vacuum breakerA Pressure Vacuum Breaker is a type of backflow prevention device, used to keep non-potable water from entering the water supply. A PVB is similar to an atmospheric vacuum breaker , except that the PVB contains a spring-loaded poppet. This makes it acceptable for applications that are high...
- 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:...
- 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...
- 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...
- 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...