Indiana property owners encounter several types of backflow prevention devices, each designed for a specific hazard level and installation condition. Understanding which device you have helps you know what annual testing involves, whether your device is appropriate for your application, and when your utility might require an upgrade.
The Four Main Types of Backflow Prevention Devices
1. Reduced Pressure Zone (RPZ) Assembly
The RPZ — also called a reduced pressure backflow preventer (RPBP) or reduced pressure zone device (RPZD) — provides the highest level of protection available and is required for all high-hazard cross-connections in Indiana.
How it works: An RPZ contains two independently acting check valves separated by a differential pressure relief valve (the “relief valve”). The relief valve is designed to open and discharge water to atmosphere when the pressure in the zone between the two check valves drops to within 2 psi of supply pressure. This ensures that even if both check valves fail simultaneously, the relief valve will open and prevent backflow — the water discharges to a drain or floor rather than reversing into the supply.
Where it’s used:
- Fire suppression and fire sprinkler systems
- Irrigation systems with chemical injection (fertilizer, pesticide)
- Commercial and industrial water connections
- Medical and dental facilities
- Car washes and high-pressure cleaning systems
- Any connection with a high-hazard cross-connection potential
Installation requirements: RPZ assemblies must be installed horizontally, above grade, and with adequate clearance above a floor drain (typically 12 inches minimum). They cannot be installed in pits or underground vaults unless the vault meets specific drainage requirements.
Annual test: The RPZ test is the most involved of all assembly tests. A certified tester measures the differential pressure across check valve #1, the differential pressure that causes the relief valve to open, and the differential pressure across check valve #2. If any component reads outside allowable tolerances, the assembly fails and must be repaired before a passing report can be submitted.
2. Double Check Valve Assembly (DCVA)
The DCVA — sometimes called a double check assembly (DCA) — is the standard protection device for low-to-moderate hazard cross-connections in Indiana. It provides less protection than an RPZ but is acceptable for a wide range of commercial and residential applications.
How it works: A DCVA contains two independently acting, spring-loaded check valves in series. Each check valve closes when downstream pressure exceeds upstream pressure, preventing backflow. Unlike an RPZ, there is no relief valve — the DCVA relies entirely on the check valves remaining closed.
Where it’s used:
- Basic residential and commercial irrigation systems (without chemical injection)
- Multi-unit residential buildings and apartment complexes
- Commercial water services with low-to-moderate hazard
- Food service and restaurant water connections (where permitted by the utility)
- Boilers and HVAC systems with non-toxic treatment chemicals
Annual test: The DCVA test measures the differential pressure across each check valve independently. The test is less complex than an RPZ test but follows a similar protocol.
3. Pressure Vacuum Breaker (PVB)
The PVB is a common and cost-effective backflow prevention device used primarily on residential and light commercial irrigation systems. It is a testable assembly that requires annual certification.
How it works: A PVB contains a spring-loaded check valve and an air inlet valve. When water flow stops and downstream pressure drops, the air inlet opens, allowing air into the line and breaking any vacuum or siphon that could cause backflow. The check valve prevents reverse flow as long as supply pressure is present.
Critical limitation: A PVB only protects against back-siphonage — not back-pressure. If your system can develop pressure higher than supply pressure (for example, due to pumps or elevated sprinklers), a PVB is not appropriate and an RPZ may be required.
Installation requirement: PVBs must be installed at least 12 inches above the highest outlet or sprinkler head in the system. This prevents back-pressure from ever reaching the device. If your property has areas where sprinklers are installed above the assembly elevation, you likely need an RPZ instead.
Where it’s used:
- Residential irrigation systems (most common application)
- Light commercial irrigation without chemical injection
- Hose connection assemblies
Annual test: The PVB test checks that the check valve holds under pressure and that the air inlet opens correctly. It is the simplest annual test of the three testable assemblies.
4. Atmospheric Vacuum Breaker (AVB)
The AVB is the simplest backflow prevention device — a small fitting typically found on individual hose bibs, laboratory faucets, and low-hazard outlets. AVBs do not require annual field testing in most Indiana utility programs.
How it works: An AVB contains a float check that seals under supply pressure and opens to atmosphere when pressure drops, admitting air and breaking the vacuum. Unlike PVBs, AVBs cannot be under continuous pressure — they must be installed where the downstream side is open to atmosphere when not in use.
Limitations:
- Cannot be used where downstream pressure can exceed supply pressure
- Cannot be installed where a downstream valve is present (the float will seal under constant pressure and fail)
- Not acceptable for use with chemical injection or high-hazard applications
- Not testable under pressure — requires periodic visual inspection only
AVBs are appropriate only for low-hazard applications. For any application with annual testing requirements, one of the three testable assemblies (RPZ, DCVA, or PVB) is required.
Which Device Do I Have?
If you’re not sure which type of assembly is installed on your property, look for the following identifying features:
- RPZ — the largest of the testable assemblies, with a prominent relief valve port on the bottom between the two check valves. Must be installed above a drain. Has a manufacturer’s nameplate identifying it as a “Reduced Pressure Zone” or “RP” assembly.
- DCVA — similar in appearance to an RPZ but no relief valve port. Has two check valves with test cocks between them. Typically installed horizontally but can be installed vertically in some configurations.
- PVB — typically installed vertically above the irrigation system, with a distinctive bonnet cover on top that houses the air inlet. Smaller than an RPZ or DCVA.
- AVB — a small inline device typically installed at the hose bib outlet, about the size of a large fist. Has a plastic or bronze bonnet on top.
If you still cannot identify your device, take a photo and share it when requesting a quote from a certified tester — they can identify the assembly type and confirm what testing is required.
Choosing the Right Device for Your Application
Your water utility’s cross-connection control program specifies which devices are acceptable for each hazard level. When in doubt, always match or exceed the required protection level. Installing a higher-protection device (like an RPZ instead of a DCVA) is always acceptable — installing a lower-protection device than required is not.
Use this directory to find a certified tester who can assess your current assembly, confirm it is appropriate for your application, and complete your annual test efficiently.