An air gap is the unobstructed space between a wall outlet and an open vessel or flood level of a fixture. An example of an air gap is the space between a faucet and the sink rim. The air gap could prevent the reverse flow of contaminated water from the sink back into the faucet without some modification of the system. It is the most economical method of preventing backflow of contaminated water back into the fresh water system.
Without air gap, the dirt water will enter and disperse into a drinking water system. Without air gap, back-siphonage would occur if the water supply in a house loses pressure and the sink is higher than point at which the water enters. This can be illustrated by attaching a hose to a faucet and submersing the hose into a sink filled with contaminated water. Under the right conditions, backflow is possible.
When an appliance such as a dishwasher is installed, the discharge hose is looped as high up under the cabinet as possible and secured with pipe straps. In this case, need an air gap to prevent backflow of water if the pump ceases to function. There are situations that make looping the hose very difficult and impractical, however, and in this situation, the installation of a mechanical air gap is required.
Plumber workers usually like to install a manufactured air gap regardless of whether or not a high loop is possible, which will provides more protection against the backflow of water. The continuous connection in the case of a high loop installation can still potentially allow back-siphoning to occur, even though the likelihood is low.
And a backflow prevention will be needed in order to prevent back-siphonage of dirty water into the water system. Plumbing inspectors are often required to analyze these fixtures to ensure that they have bee properly designed and installed. An air gap is a non-mechanical form of backflow prevention, and must be twice the inner diameter of the pipe. This fixture should be at least 1 inch (2.5 cm) in diameter in order to qualify.
In fact, it is not always practical to use an air gap to provide maximum protection against backflow. It can be bypassed by plumbers who may not have the patience or expertise to install it correctly. Despite any minor issues involved in installing this fixture, the protection it provides is well worth any installation issues.