ASSE 5120 cheat sheet

Cross-connection: any actual or potential link between a potable water system and a source of contamination or pollution.

Backflow: reverse flow of water or other substances into the potable system from any unintended direction or source.

Backsiphonage: backflow caused by negative or reduced pressure in the supply piping; driven by atmospheric pressure pushing the downstream liquid into the low-pressure zone.

Backpressure: backflow caused by downstream pressure exceeding the supply pressure; sources include boilers, elevated tanks, pumps, and thermal expansion.

Pollutant vs. contaminant: a pollutant degrades quality (taste, odor, appearance) without creating a health hazard; a contaminant creates an actual health hazard.

Degree of hazard drives device selection: high hazard (toxic or health-threatening) requires an air gap or reduced-pressure principle assembly; low hazard may allow a double check or PVB.

Two conditions must coexist for backsiphonage: a cross-connection and a pressure drop below atmospheric at that point (e.g., main break, high-demand fire flow, nearby flushing).

Air gap is the only absolute protection because it relies on a physical separation of at least twice the effective opening diameter, with no mechanical parts to fail.

1 psi equals 2.31 feet of water column head; 1 foot of head equals 0.433 psi.

Pressure at a point = static head plus applied pressure; a 100-foot column of water produces about 43.3 psi at its base.

Atmospheric pressure at sea level is about 14.7 psi (101.3 kPa); a negative gauge pressure cannot exceed -14.7 psi in theory.

Flow through a fixed orifice rises with the square root of the pressure differential: doubling the differential increases flow by about 1.41 times.

Friction loss in pipe rises roughly with the square of velocity, so doubling flow in the same pipe produces about four times the head loss per unit length.

Water hammer is a pressure surge from rapid velocity change; surge magnitude increases with fluid velocity and with shorter valve closure times.

Thermal expansion in a closed system (check valve or backflow preventer isolating a water heater) can raise pressure until a thermal expansion device or relief valve relieves it.

Cavitation occurs where local pressure falls below vapor pressure; it damages internal components and can cause a backflow preventer check to fail or chatter.

Causes of reduced supply pressure include main breaks, high fire-flow demand, elevation rise, undersized service lines, and partially closed or fouled valves.

Air gap (AG): physical separation between the supply outlet and the flood-level rim; the only non-mechanical protection and appropriate for high hazard.

Atmospheric vacuum breaker (AVB): has an air inlet that opens at atmospheric pressure; must be installed at least 6 inches above the highest downstream outlet, cannot be under continuous pressure, and cannot protect against backpressure.

Pressure vacuum breaker (PVB): spring-loaded check plus an air inlet; must be installed a minimum of 12 inches above the highest downstream outlet and cannot be used where backpressure exists.

Double check valve assembly (DCVA): two independently acting check valves with test cocks; protects against low hazard and backpressure but has no vent to atmosphere.

Reduced pressure principle assembly (RPZ/RP): two spring-loaded checks with a hydraulically dependent differential relief valve that discharges when the first check fails or when supply pressure drops; protects against both backflow types at high hazard.

Spill-resistant pressure vacuum breaker (SVB): uses a loaded air inlet check that seals to prevent spilling under normal conditions; still limited to backsiphonage protection.

Double check detector assembly (DCDA) and RP detector assembly (RPDA): fitted with a bypass meter and small check assembly to detect unauthorized flow on fire-line services.

Hose-bibb vacuum breaker (HBVB): small device for threaded hose connections; not for continuous pressure and not for backpressure protection.

Differential pressure test kit with a needle valve and sight tube is the standard instrument for testing checks and relief valves; record gauge accuracy and calibration date.

Test sequence for an RP assembly: verify first check holds, verify second check holds, then confirm relief valve opens at the specified differential and closes tight.

RP relief valve opening criterion: typically opens when the differential between the first and second check zones drops to about 2 psi or less, with the supply shut down or throttled.

DCVA test: confirm check 1 holds against reverse flow and check 2 holds; record the differential pressure at which each check holds (commonly at least 1 psi).

PVB test: verify the air inlet opens at 1 psi or more of negative pressure and the check holds at least 1 psi against reverse flow.

Before testing, confirm no flow downstream, close isolation valves, and flush test cocks; after testing, restore the assembly, check for leaks, and tag it with the test date and result.

Test gauges should be certified annually or per jurisdiction; a gauge reading error directly becomes a test-result error, so compare against a known reference.

ASSE 5110 covers backflow prevention assembly testers; the ASSE 5120 credential addresses cross-connection control program administration and device testing oversight.

Key device standards: ASSE 1001 (AVB), 1011 (hose-bibb vacuum breaker), 1012 (PVB), 1013 (DCVA), 1015 (RP), 1020 (vacuum breaker wall hydrant), 1047 (spill-resistant PVB).

AWWA and ASSE program guidance, plus state plumbing codes (such as the Uniform Plumbing Code and International Plumbing Code), set installation and testing intervals.

Typical testing frequency is annual, but local ordinance governs; some jurisdictions require testing at installation, after repair, and after relocation.

A containment policy protects the public main at the service connection; an isolation policy protects fixtures and processes inside the building.

Administrative elements of a program include an ordinance, a cross-connection survey, device inventory, tester certification, records retention, and enforcement procedures.

New construction and change-of-use permits typically trigger a cross-connection hazard assessment before the service is activated.

Only certified testers may submit test reports, and reports generally must go to the water purveyor and the local health authority within a set period.

Confined-space, trench, and hot-work entry requires permits; backflow testing near boilers or chemical injection points calls for PPE and hazard review.

Before opening a test cock, confirm downstream isolation; discharging a relief valve near electrical equipment or chemicals creates a contamination and shock risk.

Records to retain: device make, model, serial number, size, location, hazard rating, test gauge readings, tester name and certification number, and pass/fail result.

Test reports must be legible, signed, dated, and traceable; corrections should be struck through and initialed, never erased or overwritten.

Failed devices must be tagged, reported, and either repaired and retested or replaced; the water purveyor may require notification and may order service interruption.

Professional practice includes disclosing conflicts of interest (tester versus repair entity), maintaining tester certification currency, and following the purveyor's approved procedures.

Documentation supports liability defense: a complete record showing the device was tested, tagged, and reported on schedule demonstrates due diligence.