What Is the Difference Between an RPZ, DCVA, and PVB Backflow Preventer?

Overview

There are several types of backflow prevention assemblies, each providing a different level of protection. The type required for your property is determined by your water authority based on the hazard level of the cross-connection.

Reduced Pressure Zone Assembly (RPZ)

The RPZ is the highest level of testable backflow protection available. It contains two spring-loaded check valves and a differential pressure relief valve between them. If either check valve fails, the relief valve opens to discharge water to atmosphere, preventing contaminants from entering the supply.

The RPZ is required for high-hazard connections: irrigation systems with chemical injection, fire sprinkler systems with additives, healthcare facilities, car washes, and industrial processes.

Note: Because the RPZ has a relief valve that will discharge water if the device fails or is improperly operated, it must be installed in a location where relief discharge will not cause property damage.

Double Check Valve Assembly (DCVA)

The DCVA contains two independently operating spring-loaded check valves. It provides protection against backpressure and back-siphonage but does not provide an external discharge path. This makes it suitable for low-hazard connections only.

Commonly used for: commercial buildings with no significant chemical or biological hazard, fire sprinkler systems using potable water only, irrigation systems without chemical injection.

Pressure Vacuum Breaker (PVB)

The PVB protects against back-siphonage only — it does not protect against backpressure. It contains a check valve and an air inlet valve. Under normal conditions it closes; if back-siphonage occurs, the air inlet opens to break the vacuum.

The PVB must be installed at least 12 inches above the highest downstream outlet and cannot be used in buried applications. It is commonly used for irrigation systems where there is no risk of backpressure.

Important limitation: A PVB will fail if any downstream valve is ever opened while the PVB shutoff is closed (creating pressure that can damage the air inlet). It is not suitable for all irrigation configurations.