Double Check Valve Assembly: Uses and Requirements
The double check valve assembly (DCVA) is one of the four primary backflow prevention device types recognized under US plumbing codes, engineered specifically for low-hazard cross-connection control in potable water systems. This page describes the mechanical design, operational boundaries, approved use scenarios, and the classification thresholds that determine when a DCVA is the appropriate device — and when it is not. Regulatory acceptance of the DCVA varies by jurisdiction, but it is governed nationally by ASSE International standard ASSE 1015 and tested under the protocols of the USC Foundation for Cross-Connection Control and Hydraulic Research. For locating licensed testers and certified installers who work with DCVAs, the backflow listings directory is the relevant starting point.
Definition and scope
A double check valve assembly is a mechanical backflow prevention device consisting of 2 independently acting, spring-loaded check valves arranged in series within a single body, accompanied by 2 tightly closing shutoff valves and 4 test cocks. This configuration distinguishes it from a single check valve (which provides no redundancy) and from a reduced pressure zone (RPZ) assembly (which adds a pressure differential relief valve between the two checks).
The governing performance standard in the United States is ASSE 1015, published by ASSE International, which specifies minimum differential pressure, tightness, and flow resistance requirements. Listings under the USC Manual of Cross-Connection Control — maintained by the USC FCCCHR — serve as the primary approval reference for water authorities and municipalities evaluating which assemblies may be installed on their distribution systems.
The DCVA is classified as a low-hazard device. Under the cross-connection control frameworks established by the U.S. Environmental Protection Agency Cross-Connection Control Manual, low-hazard designations apply to scenarios where a reverse flow event would introduce an aesthetically objectionable — but not health-threatening — contaminant into the potable supply. High-hazard applications, where toxic or biological contamination is possible, require an RPZ assembly instead.
Permitting and inspection requirements for DCVA installations are set at the state and local level. Most jurisdictions require installation by a licensed plumber and annual testing by a certified backflow prevention assembly tester (BPAT). The backflow-directory-purpose-and-scope page describes how this professional credentialing landscape is organized nationally.
How it works
The double check valve assembly operates on a differential pressure principle. Under normal forward flow conditions, water pressure from the supply side forces both check valves open, allowing flow to continue downstream. When forward pressure drops or downstream pressure rises — the two conditions that produce backflow — the spring-loaded checks close independently, blocking reverse flow through 2 separate mechanical barriers.
The redundant design matters because individual check valve discs can foul, warp, or seat improperly due to debris, scale, or thermal cycling. With 2 checks in series, a single fouled disc does not compromise the assembly's ability to prevent reverse flow.
Functional components, in flow order:
- Upstream shutoff valve — isolates the assembly for testing and maintenance without draining the downstream piping
- First check valve — spring-loaded disc; closes when forward differential drops below the spring's crack pressure (typically 1.0 psi minimum under ASSE 1015)
- Second check valve — independent spring-loaded disc providing the redundant barrier
- Downstream shutoff valve — isolates the downstream side during testing
- 4 test cocks — located at defined positions to allow a certified tester to verify differential pressure across each check using a differential pressure gauge kit
Testing procedure follows protocols defined by the American Water Works Association (AWWA M14, Recommended Practice for Backflow Prevention and Cross-Connection Control) and by state-specific plumbing authority regulations. During a test, the tester measures the closing differential of each check and the tightness of each shutoff valve. A DCVA fails testing if either check valve closes at a differential below the minimum threshold specified in ASSE 1015 or if a shutoff valve leaks past its seat.
Common scenarios
The DCVA is approved for installation in low-hazard cross-connection contexts across commercial, institutional, and residential applications. Typical deployment scenarios include:
- Commercial irrigation systems (non-chemical injection) connected to a potable supply, where the downstream hazard is non-potable water rather than fertilizer or pesticide
- Fire sprinkler systems using domestic water supply with no antifreeze additives — a scenario frequently governed by NFPA 13 installation requirements in coordination with local water authority cross-connection programs
- Booster pump installations in multi-story buildings where pump operation creates backpressure conditions
- Cooling tower makeup water lines classified as low-hazard by the authority having jurisdiction (AHJ)
- Residential connections to supplemental water sources such as private wells, where the hazard classification has been assessed as non-health-threatening
The DCVA is also frequently specified for multi-family residential buildings at the meter, protecting the utility distribution system from building-side backpressure caused by building pump systems or thermal expansion in closed plumbing loops.
Decision boundaries
The central decision boundary for DCVA use is the hazard classification assigned to the cross-connection being controlled. This classification is the authority having jurisdiction's determination, typically made by the local water utility's cross-connection control program in reference to state plumbing code and EPA guidance.
DCVA vs. RPZ — key distinctions:
| Factor | DCVA | RPZ Assembly |
|---|---|---|
| Hazard level | Low (pollution) | High (contamination) |
| Governing ASSE standard | ASSE 1015 | ASSE 1013 |
| Relief valve present | No | Yes |
| Approved for toxic/biological risk | No | Yes |
| Installation orientation | Horizontal (primarily) | Horizontal only |
| Typical applications | Irrigation (no chemicals), fire suppression (no additives), cooling makeup | Chemical injection, medical/laboratory, food processing |
A DCVA cannot be substituted for an RPZ assembly when the AHJ has classified a cross-connection as high-hazard. Conversely, RPZ assemblies are not automatically superior to DCVAs in low-hazard settings — they introduce a relief port that discharges water during pressure fluctuations, creating drainage and installation complexity that is unnecessary where low-hazard protection is sufficient.
Orientation and installation constraints also affect device selection. Most manufacturers and ASSE 1015 testing protocols qualify DCVAs for horizontal installation; vertical installation (flow upward or flow downward) requires explicit manufacturer listing confirmation and AHJ acceptance. Some larger assemblies — 2.5 inches and above — carry installation restrictions that differ from smaller residential-scale units.
Inspection and permitting: Most state plumbing codes require a permit for any new DCVA installation, with inspection at rough-in and final. Annual testing by a BPAT certified by the American Backflow Prevention Association (ABPA) or an equivalent state program is the standard maintenance requirement. Test records are typically submitted to the water utility and retained by the building owner. For context on how this service sector is organized and how to navigate it, see how-to-use-this-backflow-resource.
References
- ASSE International — ASSE 1015 Standard for Double Check Valve Backflow Prevention Assemblies
- U.S. Environmental Protection Agency — Cross-Connection Control Manual
- USC Foundation for Cross-Connection Control and Hydraulic Research (USC FCCCHR)
- American Water Works Association — AWWA M14: Recommended Practice for Backflow Prevention and Cross-Connection Control
- American Backflow Prevention Association (ABPA)
- NFPA 13 — Standard for the Installation of Sprinkler Systems