Backflow is the unwanted reverse flow of water from a building’s plumbing or fire sprinkler system back into the public water supply. In a fire sprinkler system, this is a concern because the water sitting in the piping, especially in systems with certain additives or in older piping with corrosion byproducts, is not intended to mix with the drinking water supply. A backflow preventer creates a mechanical barrier that stops this reverse flow from occurring, protecting the public water system’s integrity.
| Characteristic | Double Check Valve Assembly | Reduced Pressure Zone (RPZ) Assembly |
|---|---|---|
| Mechanism | Two independent check valves in series | Two check valves plus a pressure-relief valve between them |
| Protection Level | Protects against backflow for moderate hazard applications | Higher level of protection, required for higher hazard classifications |
| Water Discharge | No water discharge under normal operation | Can discharge water through the relief valve if a check valve fails, by design |
| Typical Setting | Standard commercial fire sprinkler connections | Higher-hazard connections, or where required by local water authority |
| Who Decides Which Is Required | Local water utility and/or AHJ hazard classification | Local water utility and/or AHJ hazard classification |
The RPZ assembly’s ability to discharge water through its relief valve is not a malfunction, it is the design working as intended, releasing water to atmosphere rather than allowing any contaminated water to flow backward if one of its check valves fails. This is also why RPZ assemblies require a floor drain or other means of handling that discharge, which double check assemblies generally do not need.
Local water utilities classify water connections by hazard level, and that classification, not simply the building owner’s preference, often dictates which type of backflow preventer is required. A fire sprinkler connection at a property the utility considers higher risk, due to the specific system design, chemicals used, or connection configuration, may be required to use an RPZ assembly regardless of what a double check assembly would otherwise accomplish. Some jurisdictions also simply mandate RPZ assemblies for all fire sprinkler connections as a matter of standard policy.
Backflow preventers require annual testing by a certified backflow tester, separate from your fire sprinkler system’s own NFPA 25 inspection schedule, though the two are often coordinated together since they involve related components of the same overall water supply system. Testing confirms the check valves and, for RPZ assemblies, the relief valve are functioning correctly and provide the level of protection the assembly is rated for.
Check with your local water utility to confirm the required backflow prevention classification for your specific connection, and have a fire protection contractor or certified backflow tester assess your current assembly to confirm it matches that requirement. A mismatch between what is installed and what your water utility requires is a compliance gap worth resolving proactively rather than discovering during a utility audit or a permit review for unrelated work.
Only if your local water utility and hazard classification allow it for your specific connection. This is generally not a matter of owner preference, it’s set by the water authority’s requirements for your specific situation.
This can be normal operation if a check valve within the assembly is not sealing perfectly, causing the relief valve to discharge slightly to prevent any backflow risk. Frequent or significant discharge should be reported to your backflow tester or fire protection contractor for assessment, since it can also indicate a component needing repair.
No. Backflow preventer testing is typically performed by a certified backflow tester on its own annual schedule, separate from your fire sprinkler system’s NFPA 25 inspection, though many buildings coordinate the two for convenience.
A failed test requires repair or replacement of the assembly before it can be certified as passing. Your water utility may also require documentation of the correction within a specific timeframe.
RPZ assemblies typically cause a somewhat greater pressure drop than double check assemblies due to their additional components, which is a factor your fire protection engineer accounts for when designing or evaluating your system’s overall hydraulic performance.
Firemax Fire Protection coordinates backflow preventer assessment and fire sprinkler system compliance for buildings across South Florida.
Firemax Fire Protection | Florida Licensed Fire Protection Contractor | Miami-Dade, Broward, Palm Beach & Monroe Counties | Est. 1998