Choosing the Right Defense: Common Types of Backflow Assemblies Explained

Protecting our clean water supply from contamination is crucial. Backflow prevention assemblies are the specialized plumbing devices designed to do just that, stopping potentially hazardous water from flowing backward into potable water lines.

But not all backflow situations are the same, which is why there isn't just one type of preventer.Understanding the common types helps clarify why a specific device might be required for your property or irrigation system.

The choice depends mainly on the level of hazard posed by the potential cross-connection. Here's a look at some frequently encountered backflow assembly types:

Reduced Pressure Zone Assembly (RPZ or RPZ A)

• Protection Level: Highest. Designed for high-hazard situations where backflow could introduce toxic substances (chemicals, sewage, etc.) into the drinking water.

• How it Works: Features two independent check valves plus a hydraulically operated differential pressure relief valve located between them. If pressure conditions suggest backflow might occur, the relief valve opens to discharge water, creating an air gap and preventing contamination.

• Common Uses: Commercial buildings, hospitals, industrial facilities, irrigation systems using chemical injection (fertigation/chemigation), boiler feeds, car washes.

• Key Feature: Offers protection against both back siphonage and backpressure. Must be installed where discharge won't cause damage.

Double Check Valve Assembly (DCVA or DC)

• Protection Level: Medium. Suitable for low-to-medium hazard situations where backflow wouldn't pose a direct health threat but could affect water aesthetics or damage plumbing.

• How it Works: Consists of two independent, spring-loaded check valves in series. If one fails, the other should still prevent backflow.

• Common Uses: Lawn irrigation systems (in some areas, depending on hazard assessment), fire sprinkler systems (main lines), food processing equipment (non-toxic), commercial building supply lines.

• Key Feature: Protects against both back siphonage and backpressure. Does not have a relief valve for discharge.

Pressure Vacuum Breaker (PVB)

• Protection Level: Protects against back siphonage only, primarily in low-to-medium hazard scenarios.

• How it Works: Contains a check valve and an air inlet vent. Under normal flow, water pressure closes the air inlet. If pressure drops (potential back siphonage), the air inlet opens, breaking the vacuum.

• Common Uses: Residential and commercial lawn irrigation systems, laboratory sinks.

• Key Feature: Must be installed at least 12 inches above the highest downstream outlet (e.g., sprinkler head). Cannot protect against backpressure and cannot have shut-offs downstream.

  
  

Atmospheric Vacuum Breaker (AVB)

• Protection Level: Protects against back siphonage only in low-hazard situations.

• How it Works: Similar principle to the PVB but simpler. Relies on atmospheric pressure to open an air vent and break a siphon.

• Common Uses: Hose bibbs (outdoor faucets), utility sinks, dishwashers.

• Key Feature: Cheapest and simplest, but cannot be under continuous pressure (must have no shut-offs downstream) and must be installed 6 inches above the highest outlet. Not testable in the same way as other assemblies.

Choosing the Right Assembly is Critical

The selection of the correct backflow preventer isn't a DIY decision. It depends heavily on the specific application, the potential contaminants involved (hazard level), and, crucially, your local plumbing codes and water authority regulations.

Always consult with a licensed plumber or certified backflow specialist to ensure the right type of assembly is installed correctly for your situation, keeping your water safe and compliant.