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Backflow Valves & Vacuum Breakers

Backflow valves and vacuum breakers are both designed to prevent wastewater from mixing with the clean water supply sent to a faucet, but they do that in different ways. If you need a solution to protect water for back- or front-of-house use, you'll find it here.

The Details of Backflow Preventers & Vacuum Breakers

Backflow preventers and vacuum breakers play a critical role in plumbing systems by preventing water flow reversal that could introduce hazardous substances into clean water lines. While they share the same end goal, their mechanisms and applications differ based on the type of backflow they are designed to counter.

While vacuum breakers are specialized for backsiphonage, the broader category of backflow preventers provides comprehensive protection against both pressure-related backflow conditions — backsiphonage and backpressure — to ensure the safety and purity of water at the outlet.

Common Questions About Backflow Preventers & Vacuum Breakers

What is Backflow & How Does It Happen?

Backflow can occur in two primary ways:

Backsiphonage: This occurs when there's a negative or sub-atmospheric pressure, or vacuum, in the potable water supply, which can suck non-potable water or contaminants from a connected fixture back into the clean system. This process is similar to drinking through a straw.

Backpressure: This occurs when pressure in a non-potable system (e.g., an irrigation system with a pump, boiler, or carbonated beverage dispenser) becomes greater than the pressure in the potable water supply, forcing contaminated water backward into the clean lines.

What is a Vacuum Breaker & How Does It Work?

Vacuum breakers are specific backflow prevention devices primarily designed to protect against backsiphonage. They work by quickly introducing air into the system when a vacuum is detected. This breaks the suction, preventing the contaminated water from being drawn back.

There are two main types of vacuum breakers:

Atmospheric Vacuum Breakers (AVB) are simple, non-pressure-retaining devices often seen on outdoor hose bibbs. They must be installed at a specific height above the highest point of water use, and they cannot be under continuous pressure.

Pressure Vacuum Breakers (PVB) are more robust, can be under continuous pressure, and feature a spring-loaded check valve and an air inlet valve. They are commonly used in irrigation systems, and they also require installation at a specified height.

What is a Backflow Preventer & How Does It Work?

In a broad sense, backflow preventers encompass a wide range of devices capable of protecting against both backsiphonage and backpressure. There are also two main types of backflow preventer:

Double Check Valve (DCV) Assemblies feature two independently operating check valves in a series. They are effective against both types of backflow in low-hazard situations where the contaminant isn't a severe health risk.

Reduced Pressure Zone (RPZ) Assemblies offer the highest level of protection. They consist of two independently operating check valves with an automatic differential relief valve positioned between them. If either check valve leaks or a pressure differential occurs, the relief valve opens to discharge water to the atmosphere, ensuring contaminated water cannot enter the potable supply. RPZs are required in high-hazard applications where contaminants pose a serious health threat.