ASSE Backflow Prevention Certification: Cross-Connection Control, Devices, and Field Testing Review

Why Backflow Prevention Matters

Potable water systems are designed to flow in one direction: from the supply main to the point of use. Backflow occurs when that flow reverses, drawing contaminated water back into the clean supply. Two conditions cause backflow: back-siphonage (a negative pressure in the supply line, such as during a water-main break) and backpressure (downstream pressure exceeds supply pressure, as with a boiler or pressurized irrigation system). Either condition can introduce biological, chemical, or physical contaminants into drinking water, making cross-connection control a public-health priority enforced by state plumbing codes and local water authorities.

Cross-Connection Hazard Classification

Before selecting any assembly, you must classify the hazard on the downstream side of the connection:

• Health hazard (high hazard): The substance that could enter the potable system is toxic, poisonous, or microbiologically dangerous. Examples include chemical injection systems, sewage, boiler water with additives, and irrigation systems supplied by a non-potable source. A high-hazard cross-connection requires a high-protection assembly.
• Non-health hazard (low hazard): The substance is objectionable or aesthetically unpleasant but not a danger to health—for example, a connection to a clean water heating system without additives. A lower-protection assembly may be acceptable, depending on the authority having jurisdiction (AHJ).

Always confirm the hazard classification with your local water authority before specifying an assembly. ASSE standards and your state plumbing code both govern this determination.

The Four Major Assembly Types

Atmospheric Vacuum Breaker (AVB): Protects against back-siphonage only—it cannot protect against backpressure. It must be installed at least six inches above the highest downstream outlet and must never be under continuous pressure for more than twelve hours. The AVB is not field-testable in the same way as other assemblies and is used for low-hazard, intermittent-use applications such as hose bibbs.

Pressure Vacuum Breaker (PVB): Protects against back-siphonage only. It can remain under continuous pressure, which makes it suitable for irrigation systems. It must be installed at least twelve inches above the highest downstream outlet. The PVB contains a loaded check valve and an air inlet valve; it is field-testable.

Double Check Valve Assembly (DCVA): Protects against both back-siphonage and backpressure. Used for low-hazard applications such as fire sprinkler systems supplied by potable water and commercial dishwasher supply lines. It contains two independently acting check valves and four test cocks. It may be installed in a pit or horizontally.

Reduced-Pressure Zone Assembly (RPZ or RPZA): The highest level of protection. Used for high-hazard cross-connections. Contains two independently acting check valves separated by a reduced-pressure zone, plus a differential pressure relief valve that opens to atmosphere if the zone pressure rises above a safe differential. The relief valve discharge must drain freely; never plug it. The RPZ is appropriate for boiler-feed connections with chemical additives, reclaimed-water cross-connections, and medical or industrial facilities.

Field Testing Safety

Before any field test:

• Follow lockout/tagout (LOTO) procedures when isolating the assembly; verify zero energy before attaching or removing test equipment.
• Wear appropriate PPE: safety glasses at minimum; chemical-resistant gloves if testing near process fluids; hearing protection in loud mechanical rooms.
• Know the location of the nearest drain; the RPZ relief valve may discharge a significant volume of water during testing.
• Confirm the test kit (differential pressure gauge kit) is calibrated and within its calibration interval before use.

Field Test Procedure Overview: RPZ Assembly

The ASSE-recognized field test sequence for an RPZ uses a differential pressure gauge kit with test hoses attached to the test cocks. The critical measured value is the differential across each check valve and the pressure relief valve opening point. In brief:

1. Notify the downstream user that flow will be interrupted.

2. Attach test kit hoses to test cocks 2 and 3 (middle test cocks) with shutoff valve No. 2 closed.

3. Slowly open test cocks; bleed air from hoses; read and record differential across Check No. 1.

4. Reposition hoses to test Check No. 2 differential.

5. Test the relief valve opening differential by slowly reducing upstream pressure until the relief valve opens; record the opening differential.

6. Compare all readings to the manufacturer's minimum passing criteria and local authority requirements.

7. Complete the standard field test report form with date, location, assembly make/model/serial number, test results, and pass/fail determination.

The DCVA field test follows a similar sequence but evaluates two check valves without a relief valve; the pass/fail threshold is a minimum pressure differential held across each check.

Reporting and Certification

A completed field test report must be submitted to the local water authority or AHJ within the timeframe they require. The report documents your certification number, the assembly tested, conditions found, and whether the assembly passed or required repair. Falsifying a field test report is a violation of your certification and may carry legal consequences.

For the ASSE backflow tester certification exam, expect questions drawn from: cross-connection identification, hazard classification, assembly selection, installation requirements, test procedures and pass/fail criteria, and report completion. Know each assembly's limitations (backpressure vs. back-siphonage protection) and the conditions under which each may be installed.