Backflow Protection for a Small Commercial Building
A small commercial building has a 2 in. domestic water service, a fire sprinkler system with antifreeze in a dry-pipe attic, an irrigation system with pop-up heads and a chemical injector, and a boiler with a manual makeup water connection. The water purveyor requires containment backflow protection. The owner wants the least expensive devices that will pass inspection and asks whether a single double-check valve at the meter can cover everything.
1. Classify each connection by hazard and identify the appropriate type of backflow protection.
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The antifreeze fire sprinkler system is a high hazard because antifreeze can be forced back into the potable supply; it needs a reduced-pressure principle assembly or a reduced-pressure detector assembly, not a double check. The irrigation system with chemical injection is also high hazard and needs an RPZ or an air gap. The boiler makeup connection is high hazard and needs an RPZ or air gap. The domestic service containment device must protect the public main from the highest hazard downstream, so an RPZ at the service is appropriate. Hose bibbs need vacuum breakers.
2. Why is a single double-check valve at the meter not acceptable for this building?
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A double-check valve is intended for low-hazard cross-connections only. This building contains high-hazard connections - antifreeze, irrigation chemicals, and boiler water - that could cause contamination or illness if backsiphoned. A double check does not provide the same level of protection as an RPZ or air gap and would not be acceptable for those hazards. The containment device must protect against the highest hazard on the premises, and each high-hazard connection also needs its own protection.
3. What maintenance and testing requirements should the owner expect?
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RPZ assemblies and reduced-pressure detector assemblies must be tested by a certified tester at installation and at the interval required by the local authority, typically annually. Test cocks and shutoff valves must remain accessible. The owner should keep test reports and repair records. Air gaps require inspection for deterioration and must maintain the required separation. Vacuum breakers on hose bibbs should be checked for damage and freeze protection.