CSA B64.4 · B64.5 · B64.1.2 · B64.1.3
Backflow Prevention Assembly Types
Your water authority specifies which assembly is required based on what's connected to your water system and the risk it poses. Here's what each type does, when it's required, and what testing involves.
By Hazard Level
Which Assembly Does Your Property Need?
The governing water authority assigns the assembly type when your commercial water service is approved. You can't change it without their sign-off. If you're not sure what you have, we'll identify it when we test.
RPZ Assembly
The highest-protection assembly — two check valves plus a relief valve that dumps to drain if the first check fails. Required any time contamination could cause illness or injury: medical offices, restaurants, industrial, car washes, irrigation with chemical injection.
RPZ technical details →Double Check Valve (DCVA)
Two independent check valves in series. Used where the risk is non-health-threatening — multi-unit residential buildings, office properties, fire suppression systems without antifreeze, light commercial. Can be installed below grade.
DCVA technical details →Pressure Vacuum Breaker (PVB)
Back-siphonage protection for commercial irrigation without chemical injection. A spring-loaded check valve plus an air inlet valve that breaks vacuum if supply pressure drops. Must be installed above the highest downstream outlet.
PVB technical details →Spill-Resistant Vacuum Breaker (SVB)
Same protection principle as the PVB but with a sealed vent — no water spills from the assembly during a siphonage event. Used on lab faucets and hose connections where the standard PVB's open discharge is a problem.
SVB technical details →Quick Reference
Assembly Comparison
| Assembly | CSA Standard | Hazard Level | Backpressure? | Below Grade? | Annual Test |
|---|---|---|---|---|---|
| RPZ / RPZA | CSA B64.4 |
Severe | Yes | No — relief valve requires drain | Yes |
| DCVA | CSA B64.5 |
Moderate | Yes | Yes | Yes |
| PVB | CSA B64.1.2 |
Minor | No — siphonage only | No — must be above outlets | Yes |
| SVB | CSA B64.1.3 |
Minor | No — siphonage only | No | Yes |
Assembly classification per CSA B64 series and National Plumbing Code of Canada 2020, Division B, Part 2
Don't know what assembly you have? That's not unusual — especially in older buildings where no one's kept records. When we arrive on-site, we identify the assembly type, confirm the manufacturer and model, and test accordingly. If it's the wrong assembly for your hazard classification, we'll note that in our report.