An air gap, as related to the

plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delive ...

trade, is the unobstructed

vertical Vertical is a geometric term of location which may refer to: * Vertical direction, the direction aligned with the direction of the force of gravity, up or down * Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...

space between the water outlet and the flood level of a fixture. Air gaps of appropriate design are required for water safety by legislation in many countries. A related term in computer security is ''network air gap''. A simple example is the space between a wall mounted faucet and the

sink A sink is a bowl-shaped plumbing fixture for washing hands, dishwashing, and other purposes. Sinks have a tap (faucet) that supply hot and cold water and may include a spray feature to be used for faster rinsing. They also include a drain t ...

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 A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in a ...

age and is the least expensive form of

backflow 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 ...

prevention. A common use of the term "air gap" in home plumbing refers to a fixture that provides back-flow prevention for an installed

dishwasher A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ty ...

. This "air gap" is seen above the sink as a small cylindrical fixture mounted parallel with the faucet. In the base cabinet under the sink, the drain hose from the dishwasher feeds the "top" of the air gap, and the "bottom" of the air gap is plumbed into the sink drain below the basket, or into a

garbage disposal unit A garbage disposal unit (also known as a waste disposal unit, garbage disposer, garburator etc.) is a device, usually electrically powered, installed under a kitchen sink between the sink's drain and the trap. The disposal unit shreds food ...

. When installed and maintained properly, the air gap works as described above, and prevents drain water from the sink from backing up into the dishwasher, possibly contaminating dishes. To further illustrate the air gap, consider what could happen if the air gap were eliminated by attaching a

hose A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called '' pipes'' (the word ''pipe'' usually refers to a rigid tube, whereas a hose is usually a flexible one), or more generally ...

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 is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ...

system.

Standards and codes

All plumbing codes require

prevention in several ways. The fixtures are manufactured to meet these codes.

Plumber A plumber is a tradesperson who specializes in installing and maintaining systems used for potable (drinking) water, and for sewage and drainage in plumbing systems.

s must not build cross-connections in their 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. According to the ''International Residential Code 2003'', 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. A standard widely use in the United States is: * A112.1.2 Air Gaps in Plumbing Systems (For Plumbing Fixtures and Water-Connected Receptors) In the United Kingdom, legislation is by statutory instrument and vary by country, but include Water Supply (Water Quality) Regulations 2016 and Water Supply (Water Quality) Regulations (Wales). The categorisation of air gaps is standardised by European standards, which cover the basic design and dimensions for appropriate to different uses. * EN 13076 -- Devices to prevent pollution by backflow of potable water - Unrestricted air gap - Family A - Type A * EN 13077 -- Devices to prevent pollution by backflow of potable water - Air gap with non-circular overflow (unrestricted) - Family A - Type B * EN 13078 -- Devices to prevent pollution by backflow of potable water - Air gap with submerged feed incorporating air inlet plus overflow - Family A, type C * and others for each family and type of air gap

References

{{DEFAULTSORT:Air Gap (Plumbing) Plumbing Backflow

Standards and codes

See also

References