InstaBidsFor homeowners
Types of backflow preventer: which one does your water line need?
Choose Air gap for end-of-the-line service where reservoirs or storage tanks are desired (EPA, 2003); Atmospheric vacuum breaker (AVB) for nonhealth or health hazards under backsiphonage only; Pressure vacuum breaker (PVB) for backsiphonage protection that could be used under constant pressure and tested in line (EPA, 2003); Double check valve assembly (DC) for nonhealth hazards only, where backpressure or backsiphonage can occur; Reduced pressure principle assembly (RP) for health or nonhealth hazards where backpressure or backsiphonage can occur; Residential dual check for nonhealth hazards only, and only on water service connections to single-family homes.
The right choice depends on whether backpressure can occur or only backsiphonage, whether the hazard is a health or nonhealth hazard, whether the line stays under constant pressure, and what your water supplier requires at your service connection.
| Type | Best for | Main advantages | Main drawbacks |
|---|---|---|---|
| Air gap | end-of-the-line service where reservoirs or storage tanks are desired (EPA, 2003) | EPA (2003): very effective where either backsiphonage or backpressure conditions may exist | EPA (2003): it interrupts the piping flow, with a loss of pressure for later use; Indiana DEM: it can be bypassed easily, which entirely destroys its effectiveness |
| Atmospheric vacuum breaker (AVB) | nonhealth or health hazards under backsiphonage only | EPA (2003): when installed properly, it can give excellent protection against backsiphonage | Indiana DEM: not designed to protect against backpressure; EPA (2003): it cannot be tested once it is installed in the plumbing system; EPA (2003): it "must not have shutoffs downstream, and must be installed at least 6-inches higher than the final outlet" |
| Pressure vacuum breaker (PVB) | backsiphonage protection that could be used under constant pressure and tested in line (EPA, 2003) | Florida DEP: may be used to isolate health or nonhealth hazards, against backsiphonage only | EPA (2003): it does not protect against backpressure, so "installation must be at least 6- to 12-inches higher than the existing outlet" |
| Double check valve assembly (DC) | nonhealth hazards only, where backpressure or backsiphonage can occur | EPA (2003): may be used under continuous pressure and protects against both backsiphonage and backpressure | Indiana DEM: protects against non-health hazards only |
| Reduced pressure principle assembly (RP) | health or nonhealth hazards where backpressure or backsiphonage can occur | Indiana DEM: compared with a double check valve, it gives a visible indication of malfunctioning long before a danger of backflow exists; EPA (2003): can be used under constant pressure and at high hazard installations | Indiana DEM: backflow assemblies are not recommended in a confined space; for example, the RP cannot be installed in pits |
| Residential dual check | nonhealth hazards only, and only on water service connections to single-family homes | EPA (2003): it was introduced to give individual residences backsiphonage and backpressure protection | Florida DEP: it usually has no shutoff valves, may or may not have test cocks or ports, and is generally less reliable than a double check valve assembly |
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| Priority | Choose |
|---|---|
| a high hazard installation on a line under constant pressure (EPA, 2003) | Reduced pressure principle assembly (RP) |
| a low to medium hazard installation (EPA, 2003) | Double check valve assembly (DC) |
| a vacuum breaker that can stay under constant pressure and be tested in line (EPA, 2003) | Pressure vacuum breaker (PVB) |
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Sources for the facts on this page
- U.S. Environmental Protection Agency (EPA), Cross-Connection Control Manual (February 2003), government, read 17 October 2026.
- Indiana Department of Environmental Management (IDEM), Cross Connection Control and Backflow Prevention Manual (2016 Edition), government, read 17 October 2026.
- Florida Department of Environmental Protection (DEP), Cross Connection Control and Backflow Prevention Program, government, read 17 October 2026.