Atmospheric Vacuum Break Backflow Preventers
When looking for backlow prevention devices for backflow, residencies typically go for atmospheric vacuum breakers (AVBs). By allowing air into the pipe, a siphon cannot form and the backflow cannot occur.
Normally made from brass, they will be formed in a 90 degree angle. As well as being relatively cheap and easy to install, they don’t require any major maintenance and last for years to come. When they are checked, InterNACHI inspectors will look for many factors including;
- Firstly, if an enclosure contains air contaminants, the AVB cannot be in the same area. When contaminated air enters the water piping, it can and most likely will lead to a poisoning in the water supply.
- Secondly, there must be a 6 inch gap between the AVB and any higher point (downstream). With this in mind, they absolutely cannot be placed below grade. Once they are installed at this distance above grade, the inspector will check the distance to any other point in the system going downstream.
- In any 24 hour period, the AVB cannot be in continuous use for half of this time otherwise malfunction is likely.
- Because it would lead to continuous pressure and use which, in turn, leads to malfunction, the shut-off valve cannot be installed downstream of the AVB.
- If there is any spillages of water from the AVB’s top, this suggests that a replacement is necessary.