ASSE 5110 cheat sheet

Backflow happens by only two mechanisms: backsiphonage (supply pressure drops below atmospheric) and backpressure (downstream pressure exceeds supply pressure).

Backsiphonage is driven by atmospheric pressure (about 14.7 psi at sea level) pushing non-potable liquid into a supply that has gone negative; the pump does not pull it in.

Common backpressure sources: booster pumps, boilers and heat exchangers, elevated storage, compressed air or gas, and chillers.

Elevation/pressure formulas for water at 62 F: psi = feet x 0.433; feet = psi x 2.31; the same math gives the backpressure created by any elevation difference in a system.

Boyle's law P1V1 = P2V2 governs expansion of trapped air or gas: halving the pressure of a fixed mass of air doubles its volume, so a depressurized tank or line can push its contents backward.

Transient surge (water hammer, sudden valve closure, main break) can drop line pressure below atmospheric for a few seconds, producing backsiphonage in a system whose static pressure is normally adequate.

Hazard classification: high hazard = contamination (toxic or health-threatening); low hazard = pollution (aesthetic or nuisance only). The hazard drives assembly selection.

The critical level is the flood level rim of the lowest fixture served, or the marked critical level of an assembly; nothing that could carry contamination may sit above it.

The Safe Drinking Water Act (1974, amended 1986 and 1996) authorizes EPA national drinking water standards; states accepting primacy adopt and enforce cross-connection control rules, usually delegated to local health departments.

The local ordinance, not the plumbing code alone, sets testing frequency, tester certification requirements, report deadlines, fees, and enforcement authority.

Containment protects the public main at the service connection; isolation protects individual fixtures, zones, or processes inside the premises. Most ordinances mandate containment and require isolation for high-hazard internal uses.

Key product standards: ASSE 1001 (atmospheric vacuum breaker), 1011 (hose-connection vacuum breaker), 1012 (double check), 1013 (reduced pressure principle), 1015 (pressure vacuum breaker), 1047 (RP detector), 1048 (double check detector), 1056 (spill-resistant vacuum breaker).

Assemblies are listed by the USC Foundation for Cross-Connection Control and Hydraulic Research, whose published list gives approved models, sizes, and flow capacities and is updated annually.

AWWA Manual M14 is the recommended practice for backflow prevention and cross-connection control programs.

Model plumbing codes: IPC Chapter 6 (Section 608) and UPC Chapter 6; fire sprinkler lines are additionally governed by NFPA 13/14 and local fire codes, which still require annual backflow testing.

Canadian practice: CSA B64.10 covers selection and installation of backflow preventers; CSA B64.10.1/2 covers field testing, maintenance, and tester competence.

Typical testing triggers: initial installation, annual interval, after any repair or internal part replacement, after relocation or re-piping, and after a meter change or service interruption.

Air gap is the highest level of protection; the separation must be at least 1 inch or twice the diameter of the effective opening, whichever is greater.

Atmospheric vacuum breaker (ASSE 1001): non-testable, no downstream shutoff valve, no continuous pressure, and the critical level must sit at least 6 inches above the highest downstream outlet.

Pressure vacuum breaker (ASSE 1015): testable, has a spring-loaded check and an air inlet, needs at least 12 inches of elevation above the highest downstream outlet, and may not be used where backpressure can develop.

Reduced pressure principle assembly (ASSE 1013): two independent check valves plus a differential relief valve, protects against both backpressure and backsiphonage, suitable for high hazard; must be installed above grade with the relief discharge terminating through an air gap to a drain.

Double check assembly (ASSE 1012): two check valves, no relief, low hazard only; it cannot relieve thermal expansion and must not be used on high-hazard or toxic connections.

Detector assemblies (ASSE 1047 RPDA, 1048 DCDA) combine a main assembly with a metered bypass to detect leakage or unauthorized draw on fire lines and other normally closed piping.

Barometric loop: a fixed 35-foot inverted U; protects against backsiphonage only and provides no backpressure protection.

Spill-resistant vacuum breaker (ASSE 1056) may be subjected to continuous pressure and does not spill from the air inlet under normal flow; a standard atmospheric breaker may not.

Non-testable point-of-use devices (hose bibb breaker ASSE 1011, dual check with atmospheric port ASSE 1052) are for low-hazard, fixtures-only protection and are never a substitute for containment.

A reduced pressure assembly has four test cocks: 1 upstream of check 1, 2 between the checks, 3 downstream of check 2, and 4 at the relief valve zone.

RP acceptance values: relief valve opens at 2.0 psi differential or higher; check 1 holds at least 5.0 psi static differential with the downstream side bled; check 2 holds 1.0 psi backpressure with no drip.

Double check acceptance values: check 1 must hold 1.0 psi backpressure and check 2 must hold 1.0 psi backpressure; anything less is a failure regardless of flow performance.

PVB acceptance values: the check valve must hold 1.0 psi backpressure and the air inlet must open at a differential of 1.0 psi or less.

Test sequence rules: flush every test cock before connecting hoses, open and close cocks slowly, bleed air from hoses, and record the actual gauge readings at each step rather than a pass/fail only.

Test kit requirements: a differential gauge readable to 0.1 psi with accuracy of about plus or minus 0.5 psi (or 2 percent of full scale), plus a current calibration certificate carried with the kit.

The relief valve opening point is determined by admitting pressure into the zone between the checks and noting the differential at which discharge begins; a reading below 2.0 psi means the relief is opening too early.

A failed assembly must be tagged, reported as failed, repaired, and fully retested; a partial or altered test form is not acceptable documentation.

Do not test a fire-line assembly without notifying the fire department or monitoring company and providing an impairment fire watch where required.

RP relief valve discharging steadily with no downstream flow: check 1 is fouled, damaged, or missing its loading, or upstream pressure has been lost; inspect check 1 and the inlet first.

RP relief discharging when downstream flow starts or when downstream pressure drops: excessive pressure drop across check 1 from scale or debris, or a clogged relief sensing passage.

Intermittent RP relief discharge: suspect thermal expansion from a water heater, water hammer, or swings in supply pressure rather than a defective check.

Check valve chatter or flutter: worn disc, damaged seat, broken or fatigued spring, or flow below the manufacturer's minimum; disassemble and install the OEM repair kit.

Use only original manufacturer repair parts; substituting springs or discs changes the certified opening points and voids the assembly's listing.

Lubricate rubber seats and O-rings only with manufacturer-approved silicone or water-based lubricant; petroleum-based grease swells and degrades EPDM and Buna-N.

Typical maintenance cycle: annual field test plus internal inspection every few years; rebuild kits commonly last one to five years depending on water quality and debris loading.

Keep the upstream strainer clean on RP assemblies; debris passing the strainer is the most common cause of check and relief malfunction.

Freeze protection matters: trapped water in RP, PVB, and sensing passages can crack bodies and burst relief components, so drain or protect assemblies in unheated spaces.

A complete test report records assembly make, model, size, serial number, location and service address, hazard classification, each gauge reading, tester name and certification number, test date, gauge ID and calibration date, and pass/fail.

A durable tag on the assembly carries the test date, tester identity, results, and next test due date so field staff can verify status without the database.

Testing frequency is usually annual; installation, repair, relocation, and re-piping each trigger a new test and a new report.

Notice cycle used by most programs: courtesy reminder 30 to 60 days before the due date, second notice after the due date, notice of violation with a hard deadline, then enforcement such as service termination or penalty.

Retention requirements are set by ordinance and commonly run three to five years; some jurisdictions require records for the life of the assembly.

The assembly inventory, keyed to meter or service numbers, drives reminder mailings, compliance percentages, and workload forecasting; detector assemblies need bypass meter readings tracked separately.

Tester oversight includes verifying certification currency (commonly recertified every two to three years), auditing a sample of submitted reports, and comparing reported values against reinspection results.

Program performance measures: percent of known assemblies tested on time, number overdue, repeat-failure rate, and average days from notice to compliance.