Backflow Prevention Devices

Backflow prevention devices operate by allowing water to flow in only one direction. In an unprotected water service connection, potable water can flow both in and out of a building or fixture. When water service is interrupted in the street or in a building for any reason, there is a pressure drop which can draw contaminated water backwards into the water system. For example, cleaning fluids may be drawn back from car washes; stagnant water from fire sprinkler systems may enter the drinking waterline; bacteria and pathogens of all sorts can be siphoned back into the water system from air conditioning cooling towers; and chemicals from medical clinic's X-ray development may flow backwards into the potable water system. To protect water quality, backflow protection is required where the end user poses a risk of polluting the city's water supply.

Types of Devices

Air Gap: An air gap is a vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel.

Reduced Pressure Backflow Prevention Assembly (RP): An RP is a mechanical backflow preventer that consists of two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve between the check valves and below the first check valve.

Double Check Valve Assembly (DC): A DC is a mechanical backflow preventer that consists of two independently acting, spring-loaded check valves.

Pressure Vacuum Breaker Assembly (PVB): A PVB is a mechanical backflow preventer that consists of an independently acting, spring-loaded check valve and an independently acting, spring-loaded, air inlet valve on the discharge side of the check valve.

Pictures provided by the American Backflow Prevention Association.