A backflow prevention device prevents contaminated water from flowing back into the potable water distribution system should a backflow condition, such as backpressure or backsiphonage, occur.
Types of Backflow prevention devices
The type of backflow prevention device required under West Virginia State law depends on the degree of hazard that exists or may exist. The greater degree of health hazard potential present means a greater amount of backflow prevention protection required. There are six basic types of backflow prevention devices.
Air Gap – The air gap is a non-mechanical backflow preventer. It is characterized as a physical separation between the potable water and contaminated water. It is very effective against a backsiphonage or backpressure condition. This is one of the oldest forms of backflow prevention.
Barometric Loop – This form of backflow prevention is also a non-mechanical backflow device. The barometric loop consists of a continuous section of supply piping that abruptly rises to the height of approximately 35 feet and returns back to the original level. It is effective in protecting against backsiphonage but not backpressure.
Atmospheric Vacuum Breaker – This is the simplest of all the mechanical backflow prevention devices. It provides protection against backsiphonage but not backpressure.
Pressure Vacuum Breaker – This device is also a mechanical backflow prevention device. It provides protection against backsiphonage but not backpressure.
Double Check Valve Assembly – This is a mechanical, testable device. It consists of two single, independently acting valves with watertight valves located at each end of the assembly and four test cocks. During normal operation both valves remain closed until there is a demand for water. If a backflow situation occurs, both valves close to prevent reversal of water flow. This type of assembly is used to protect against both backsiphonage and backpressure. However, it should only be used in low health hazard situations.
Note: Two standard plumbing check valves in series may not be used in place of the double check valve assembly because of the necessity for testing.
Double Check with Atmospheric Vent – This is a mechanical, testable device. It consists of two valves and an atmospheric vent between the two valves. During normal operation, both valves remain closed until there is a demand for water. Depending on the type of backflow condition, either, backsiphonage or backpressure, the valves close or the atmospheric vent opens to prevent the reversal of water flow. It is effective for both backsiphonage and backpressure. This type of device is used only in non-health hazard situations.
Below is a link to a video showing how the double check valve with atmospheric vent backflow preventer works.
Reduced Pressure Principal Backflow Preventer – This is a mechanical testable device. It consists of two single, independently acting valves, an automatically operated pressure relief valve, watertight valves located at each end of the assembly and four test cocks. During normal operation, both valves remain closed until there is a demand for water. However, depending on the type of backflow condition, either backsiphonage or backpressure, the valves either close or the relief valve will open, in order to prevent the reversal of water flow. This valve type is excellent protection in high health hazard installations.
Below is a link to a video showing how the reduced pressure backflow preventer works.