Backflow Prevention Device: Definition & Technical Guide
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A backflow prevention device is a mechanical assembly installed in a plumbing system to prevent contaminated water from flowing backward into the potable water supply. These devices use check valves, air gaps, or pressure-differential chambers to ensure water moves in only one direction, protecting drinking water from cross-contamination caused by backpressure or back-siphonage events.
One-Way Flow, Hazard Classification & Testing Requirements
Backflow prevention devices function as one-way gates within a plumbing system. When water flows in the intended direction, the device opens and allows normal passage. When flow reverses or pressure conditions change, the device closes automatically and blocks backward movement. This mechanical safeguard complements the physical air gaps built into fixtures and provides protection at points where direct connections to non-potable sources exist.
The level of protection a backflow prevention device provides depends on its design. Simple devices like hose bib vacuum breakers protect against back-siphonage only and are suitable for low-hazard connections. Complex assemblies like reduced-pressure zone (RPZ) devices protect against both backpressure and back-siphonage and are required for high-hazard connections where contamination could cause illness or death.
Every backflow prevention device requires regular testing to verify that its internal components are functioning correctly. Springs weaken, check valves accumulate debris, and rubber seals deteriorate over time. A device that appears to be installed correctly may fail to activate when needed if its internal components are compromised.
RPZ, Double Check, Pressure Vacuum Breaker & AVB Types
Reduced-pressure zone (RPZ) assemblies provide the highest level of mechanical protection. They contain two independently operating check valves separated by a pressure-monitored relief zone. If either check valve fails, the relief valve opens and discharges water to atmosphere rather than allowing contamination to pass. RPZ devices are required for high-hazard installations.
Double check valve assemblies (DCVA) contain two independently operating check valves in series. They protect against both backpressure and back-siphonage but lack the monitored relief zone of an RPZ. DCVAs are used for medium-hazard connections like irrigation systems and fire sprinkler lines.
Pressure vacuum breakers (PVB) protect against back-siphonage only. They include a check valve and an atmospheric vent that opens when supply pressure drops. PVBs are common on residential irrigation connections and must be installed at least 12 inches above the highest downstream outlet.
Atmospheric vacuum breakers (AVB) are the simplest and least expensive option. They provide back-siphonage protection only and cannot be used with continuous pressure or downstream shutoff valves.
Installation, Annual Testing & Certification Services
Bonded Plumbworks’ backflow prevention services include device selection based on hazard classification, professional installation, annual testing and certification, and repair or replacement of failed assemblies. Most water authorities require annual testing of all installed backflow prevention devices by certified testers, and test reports must be filed with the local water authority.
During a plumbing inspection, technicians identify unprotected cross-connections and recommend the appropriate device class. Irrigation systems, water heaters in closed systems, and swimming pool fill lines are the most common residential connection points requiring backflow prevention devices.
ASSE 5000 Series, ASSE 1013 & AWWA M14 Standards
The ASSE 5000 series standards govern backflow prevention device design and testing. ASSE 1013 covers RPZ assemblies, ASSE 1015 covers DCVAs, and ASSE 1020 covers PVBs. The State building codes require backflow prevention on all connections classified as health hazards by the local water purveyor. The AWWA M14 manual provides the industry-standard guidelines for cross-connection control programs.
USC Foundation for Cross-Connection Control and Hydraulic Research maintains the approved list of backflow prevention assemblies that local jurisdictions reference.
Watts Series 009, Febco 825Y & Zurn Wilkins 375 Examples
Watts leads the market with the Series 009 RPZ and Series 007 DCVA, widely specified for commercial and residential applications. Febco (Watts) produces the Series 825Y RPZ for commercial applications. Wilkins (Watts) manufactures residential-grade double check assemblies. Zurn offers the Wilkins 375 series for high-flow commercial installations.
Related Plumbing Terms
- Backflow
- Check Valve
- Double Check Valve
- Air Gap
- Reduced Pressure Zone Device