Backflow Prevention Testing Reference

Why this matters

Backflow assemblies protect the public water supply from contamination. They sit between the building's potable water service and any cross-connection (irrigation, fire sprinkler, boiler, commercial chemical equipment) where a pressure drop could siphon non-potable water back into the main. Most jurisdictions require ANNUAL certified testing - and only a state-certified backflow tester can sign the report. Skip a year and the water utility shuts off service. The test itself is a 20-30 minute process with a calibrated differential pressure gauge; documenting and submitting is sometimes more work than testing.

What backflow is

Two scenarios where water flows the wrong direction:

Back-siphonage: the supply main loses pressure (line break, firefighting use, peak demand) and creates a vacuum. Water in connected non-potable systems gets sucked back into the main. Example: hose end submerged in a swimming pool, pressure drops, pool water enters the house and the public main.

Back-pressure: the downstream system is at HIGHER pressure than the supply (booster pump, pressurized boiler, elevated tank). Water flows backward through the connection regardless of supply pressure. Example: industrial process water in a closed loop at 150 psi, supply is 60 psi - process water flows back into supply.

Each requires a specific protection assembly type matched to the hazard level.

Assembly types (low to high hazard)

AVB - Atmospheric Vacuum Breaker:

• Lowest level protection
• Protects against back-siphonage only (not back-pressure)
• No moving parts under normal flow; opens to atmosphere when supply pressure drops
• Cannot be installed where it would be subject to backpressure or continuous pressure (>12 hr at a time)
• Common use: garden hose bibs (vacuum breaker built into modern frost-free sillcock)
• Not field-testable - visual inspection only

PVB - Pressure Vacuum Breaker:

• Protects against back-siphonage under continuous pressure
• Spring-loaded; has a 1st check + air inlet
• Common use: residential lawn irrigation systems
• Testable with differential pressure gauge

DCV - Double Check Valve Assembly:

• Two independent spring-loaded check valves in series
• Protects against both back-siphonage AND low-hazard back-pressure
• Common use: fire sprinkler systems (low-hazard), some boiler feed
• Testable

RP / RPZ - Reduced Pressure Zone Assembly:

• Two check valves with a relief valve between them
• Maintains a pressure zone between the checks LOWER than supply pressure
• If either check fails, relief valve dumps to atmosphere (visible flooding from the relief - that's the signal of a failure)
• Highest level of protection; required for high-hazard connections (medical, lab, irrigation with chemical injection, commercial process)
• Testable

Where each is required (typical residential)

Always check local AHJ - water utilities have authority to require higher protection than minimum code.

Testing requirements

• Annual test in most jurisdictions; some require semi-annual or biennial
• State-certified tester must perform and sign the test report - typically a 16-40 hour cert course + exam (ASSE, AWWA, or state-administered)
• Calibrated differential pressure gauge required (typical: Watts TK-99E, Mid-West Instrument 845, Backflow Direct DPG-1) - calibrated annually by an accredited lab
• Test report submission to the water utility within a certified-tester-specific time window (usually 30 days)
• Failed assembly: must be repaired or replaced and retested within the AHJ's grace period (often 30-90 days)

Test procedure (RPZ - most common testable type)

This is a generalized procedure; specific assemblies vary slightly. Always follow the manufacturer's test procedure for the exact assembly.

Tools: Calibrated 3-valve differential pressure gauge with hoses, brass needle-valve test cocks (often built into the assembly), wrench for test-cock plugs.

1. Notify the customer that water flow will be interrupted briefly. Schedule around occupant needs.

2. Inspect the assembly visually:

• Relief valve dripping? → mid-zone pressure too high (1st check leaking) - likely fail.
• Visible leaks anywhere? → fail.
• Body cracked, corroded? → fail.
• Test cocks accessible and operational?

1. Connect the test kit per the manufacturer's diagram - three hoses to three test cocks on the assembly. Hose color and test cock number per the diagram.

2. Open test cocks slowly per the procedure. Bleed air from each hose.

3. Close the downstream shutoff valve (No. 2 shutoff, on the assembly).

4. Test 1st check: record differential pressure (mid-zone pressure minus supply pressure). Acceptance: 1st check holds at least 5 psid for 1 minute.

5. Test 2nd check: different procedure depending on kit / assembly. Acceptance: 2nd check holds at least 1 psid.

6. Test relief valve: open relief valve test cock slowly until relief opens. Record opening pressure. Acceptance: opens at >2 psid.

7. Restore the assembly:

• Close test cocks
• Disconnect hoses
• Re-open downstream shutoff slowly
• Confirm normal water flow downstream

1. Document on the test report form (state-specific):

• Tester name and certification number
• Assembly type, manufacturer, model, serial
• Test results (1st check, 2nd check, relief opening)
• Pass / fail
• Submit to water utility per requirements

Common failures and repairs

Relief valve drips constantly:

• 1st check is failing (water leaking through into mid-zone, raising pressure above relief setpoint)
• Repair: replace 1st check internals (spring, disc, seat) - manufacturer's repair kit
• Or replace entire assembly if old or repair-kit unavailable

1st check fails on test (doesn't hold differential):

• Disc fouled, spring weak, seat damaged
• Repair kit replacement OR full assembly

2nd check fails:

• Similar - disc, spring, or seat issues
• Repair kit

Relief valve doesn't open at proper setpoint:

• Relief diaphragm or spring degraded
• Repair kit

References

• AWWA M14 (Recommended Practice for Backflow Prevention and Cross-Connection Control)
• ASSE 5000 / 5010 / 5020 / 5050 series (backflow technician certifications)
• USC FCCCHR Manual (Foundation for Cross-Connection Control)
• Local AHJ rules - every water utility has specific requirements; always confirm
• Manufacturer test procedures (Wilkins, Watts, Febco, Apollo, Ames) - assembly-specific