Backflow, or water flowing in the wrong direction, creates environmental and plumbing problems and can delay fire sprinkler response times. To prevent water from backing into the supply line, backflow preventers use two one-way check valves in series. These check valves act as one-way gates, allowing water to flow in only one direction.
Being familiar with backflow devices is important because environmental damage can occur if contaminated water re-enters the water table due to backflow. Improperly protected water systems have the potential to lead to illness, and even in some cases death. As regulated by local governing boards, fire protection professionals are responsible for protecting the water supply.
Regular backflow equipment inspections are critical to ensure devices and components meet standards. Common deficiencies include inadequate testing, rust, faulty check valves, and incorrect relief valve opening points.
Protecting Lives and Property
Backflow preventers protect public drinking water supplies from contamination from non-potable sources through back siphonage and back pressure. While Double Check Valve Assemblies (DCVAs) and Reduced Pressure Zone Assemblies (RPZAs) are typical for fire protection, other backflow preventers are used in plumbing systems:
- Air Gap (AG): The most effective method is using a physical air space between potable and non-potable systems (e.g., a faucet and a sink).
- Atmospheric Vacuum Breaker Assembly (AVB): Includes an air inlet valve and check seat. During water flow, the inlet closes; when the flow stops, the inlet falls against the seat, stopping back siphonage and letting air into the system.
- Pressure Vacuum Breaker Assembly (PVB): Similar to an AVB, but with a spring-loaded air inlet valve and check valve, plus two shutoffs and two test cocks. During flow, the check valve is open, and the inlet is closed; when flow stops, the check valve closes, and the inlet opens.
- Double Check Valve Assembly (DCVA): Contains two spring-loaded check valves, two shutoffs, and four test cocks. If one check valve fails during backflow, the other closes.
- Double Check Valve Detector Assembly (DCVA): Like a DCVA, but with a bypass and smaller DCVA to allow a water meter to monitor incidental water use.
- Reduced Pressure Zone Assembly (RPZA): Provides maximum protection and is common in fire protection. It contains two spring-loaded check valves with a differential relief valve between them, plus two shutoffs and four test cocks.
- Reduced Pressure Zone Detector Assembly: Like an RPZA, but includes a bypass with a smaller RPZA for a water meter to monitor incidental water use.
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