Six device families
cover ninety-eight
percent of the work.
Each backflow-prevention assembly we test belongs to one of six families. The family is set by the hazard class of the premises and the direction of expected reversal. The family decides the test sequence, the rebuild kit, and the AHJ form.
The six families
A backflow event is either back-pressure (downstream pressure exceeds supply, e.g. a boiler that lost its expansion tank) or back-siphonage (supply pressure drops below downstream, e.g. a water-main break upstream). RPs and DCs protect against both. PVBs and SVBs protect against back-siphonage only. The detector variants (RPDA/DCDA) add a parallel low-flow meter so the utility can catch an unauthorized tap on a fire line. Below: each family with a data sheet, a USC FCCCHR-approved model list, the typical Milwaukee premises that calls for it, and the failure modes we look for.
Reduced Pressure Principle
Two checks with a vented intermediate zone held below supply pressure. The high-hazard family.
Double Check Valve
Two checks in series. The moderate-hazard standard.
Pressure Vacuum Breaker
Single check plus air-inlet vent above flood-rim. Irrigation laterals.
Spill-Resistant VB
PVB plus a spring-loaded check. Indoor PVB where the dribble would be a nuisance.
RP Detector Assembly
RP with a parallel 5/8″ bypass meter. High-hazard fire service.
DC Detector Assembly
DC with a parallel meter. Moderate-hazard fire service.
Picking the right family
Selection is set by your premises hazard class, not by your preference. Below is the abbreviated table we keep on the inside cover of the truck binder. The unabbreviated version is the USC FCCCHR Manual §3.4 plus SPS 382.41(11) Table 41.
| Premises type | Typical cross-connection | Hazard | Family |
|---|---|---|---|
| Restaurant / commercial kitchen | Beverage carbonator, soft-serve cleaner, three-comp sink | High | RP |
| Dental clinic | Vacuum / saliva ejector, amalgam separator | High | RP |
| Medical office (incl. dialysis) | Autoclave fill, eyewash, chemo prep | High | RP |
| K-12 school w/ chem lab | Lab gas fixtures, hose bibbs in art room | High | RP + RPDA |
| Light industrial / foundry | Cooling-loop glycol, quench bath, plating | High | RP |
| Multifamily ≥5 units (5–10 stories) | Boiler glycol, makeup-water | Moderate | DC |
| Office building (sealed HVAC, no boiler chem) | HVAC makeup, secondary loop | Moderate | DC |
| Fire service w/ antifreeze | Glycol-filled wet pipe | High | RPDA |
| Fire service w/o antifreeze (wet) | Stagnant water in standpipe | Moderate | DCDA |
| Lawn irrigation no injection | Stagnant lateral | High back-siph | PVB or DC |
| Lawn irrigation w/ injection (fertigation) | Chemical pulled back via siphon | High both ways | RP |
| Carwash | Soap loop, reclaim system | High | RP |
| Veterinary clinic | Surgical wash, anesthesia scavenger | High | RP |
The assembly at the premise's water-service entrance is the containment device — it protects the utility's water main from anything inside the building. The assemblies at each interior fixture (lab faucet, soda gun, autoclave) are isolation devices — they protect the building's interior water from the fixture's specific hazard. Most commercial premises in Milwaukee need both. We test both.