When an air gap is not practical, which of the following backflow prevention devices may be acceptable?

An air gap is the most effective method for preventing backflow; however, there are situations where an air gap may not be practical. In such cases, a range of backflow prevention devices can be utilized to protect the potable water supply from contamination.

The correct choice includes atmospheric vacuum breakers, pressure vacuum breakers, testable double check valve assemblies, and reduced pressure zoning devices. Each of these devices serves a specific purpose in preventing backflow in various applications:

1. Atmospheric Vacuum Breakers are devices that prevent back-siphonage by allowing air to enter the system when a negative pressure occurs, thus breaking the vacuum and preventing contaminated water from being drawn back into the potable supply.

2. Pressure Vacuum Breakers work similarly, offering protection against back-siphonage and incorporating a check valve that closes to protect the water supply when pressure drops.

3. Testable Double Check Valve Assemblies consist of two check valves in series and are designed to prevent backflow in situations where the risk of contamination is low. They must be tested regularly to ensure effectiveness.

4. Reduced Pressure Zoning Devices provide higher levels of protection by maintaining a reduced pressure zone that is lower than the pressure in the potable water system,