Types of Commercial Backflow Preventers

Not every commercial property needs the same backflow preventer. The right device depends on the degree of hazard the connection presents and what your local water authority requires. Here's an overview of the main types you'll encounter on a commercial property.

Two protection mechanisms show up across these devices, and they're not interchangeable. Backsiphonage is contamination pulled backward by negative pressure (a water main break nearby, for example); backpressure is contamination pushed backward because downstream pressure exceeds supply pressure. Some devices only guard against one of the two, which is a real factor in what your local water authority requires for a given connection, not just the hazard level.

Reduced Pressure Zone (RPZ) Assembly

Protects against: both backsiphonage and backpressure. Typically required for: higher-hazard connections where the responsible authority approves this form of protection. How it works: two independent check valves with a pressure-sensing relief valve between them that opens when the required pressure difference is not maintained. Discharge needs evaluation; it does not by itself identify the cause. Field-testable: yes. Typical use: chemical feed lines, medical/lab equipment, fire lines with additives. See our dedicated RPZ guide for more detail.

Double Check Valve (DCV) Assembly

Protects against: both backsiphonage and backpressure. Typically required for: lower-hazard connections, where local code allows it. How it works: two independently operating check valves in series, with no relief valve, so it can fail without any visible sign. Field-testable: yes. Typical use: many domestic and commercial water lines, low-hazard fire lines.

Pressure Vacuum Breaker (PVB)

Protects against: backsiphonage only, not backpressure. Typically required for: connections where code allows a backsiphonage-only device, most commonly irrigation. How it works: a check valve and an air inlet valve, and it must be installed above the highest point of use downstream. Field-testable: yes.

Atmospheric Vacuum Breaker (AVB)

Protects against: backsiphonage only, not backpressure. Typically required for: backsiphonage-only connections where the device and installation are approved for the hazard. How it works: a check mechanism and an air inlet, without test cocks for the standard field test used on testable assemblies, and it cannot be installed anywhere it would stay under continuous pressure, which is why it always sits downstream of a shutoff valve, never on a line that's pressurized around the clock. Field-testable: no. Typical use: suitable point-of-use connections and irrigation zones, subject to device-specific installation requirements.

How to Tell Which Type You Already Have

Start with the manufacturer's label and the assembly model, if accessible. Visible features can provide clues, but the application alone does not establish the device type. An RPZ assembly has a visible relief valve port between two shutoff valves, usually with a small drain or discharge point nearby. A double check valve assembly looks similar but without that relief valve or discharge point. A pressure vacuum breaker or atmospheric vacuum breaker is typically smaller, mounted above the downstream fixtures it protects. If you're not sure from a visual check, a Roto-Rooter technician can identify the device on-site during a test or inspection.

How to Know Which One You Need

The degree of hazard your connection presents, and your local water authority's specific requirements, determine which device type is correct for your property. Discuss the connection, water use and any water-provider instructions with your service team before selecting an assembly.

How Roto-Rooter Can Help

Contact your local Roto-Rooter team to discuss the services available for your backflow assembly. Visit our commercial backflow services page for the full range of services, or see commercial backflow installation and commercial backflow testing for the specifics on each.

For help with an existing installation, explore backflow inspection or backflow repair.