what is an air gap for a faucet
Air gap (plumbing) 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 siphonage and is the least expensive form of backflow prevention.
Backflow prevention device The simplest, most reliable way to provide backflow prevention is to provide an air gap. An air gap is simply an open vertical space between any device that connects to a plumbing system (like a valve or faucet) and any place where contaminated water can collect or pool. A simple air gap has no moving parts, other than flowing water. Many plumbing codes specify a minimum air gap distance required for various circumstances, such as a drain connection for a dishwasher, e.g., BS 6282.
Vapor–liquid separator For the common variety, gravity is utilized in a vertical vessel to cause the liquid to settle to the bottom of the vessel, where it is withdrawn.[1][2][3][4]
Vein Veins are less muscular than arteries and are often closer to the skin. There are valves in most veins to prevent backflow.