Air gap: The least expensive and most effective way to provide backflow prevention is to provide an air gap. 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.
Vacuum breaker: This typically contains a plastic disc that is pressed forward by water supply pressure and covers small vent holes. Should the supply pressure drop, the disc springs back, opening the vent holes which let in outside air, preventing backflow of water.
Double Check Valve Assembly: A DCVA consists of two check valves assembled in series. It’s suitable for prevention of back pressure and back siphonage but not suitable for high hazard applications. It is commonly used on irrigation, fire sprinkler and boiler systems. If the hazard is higher, such as using antifreeze in the fire sprinkler system, then a more reliable check valve such as reduced pressure backflow assembly must be used.
Reduced Pressure Backflow Assembly: This device consists of two independent check valves, plumbed in series, with a pressure monitored chamber between. The chamber is maintained at a pressure that is lower than the water supply pressure, but high enough to maintain downstream pressure. The device must be mounted in a location where the drain will not become flooded.
