Check Valves Explained: Your First Line of Defense Against Backflow

Ensuring the safety and purity of our drinking water is paramount. A significant threat to water quality is backflow – the unwanted reversal of water flow in a plumbing system, which can pull contaminants into the clean water supply.

Fortunately, specialized devices called backflow prevention assemblies protect us, and a fundamental component within many of these is the humble check valve.But what exactly is a check valve, and how does it contribute to preventing backflow?

What is a Check Valve?

At its core, a check valve, sometimes called a non-return valve (NRV), is a simple mechanical device designed to allow fluid (in this case, water) to flow in only one direction. Think of it like a one-way door or gate within your pipes. Its primary purpose is to automatically prevent reverse flow.

How Does a Check Valve Work?

The operation of a basic check valve relies on pressure differential:

1. Forward Flow: When water flows in the intended direction, its pressure pushes open a disc, flap (swing check), or poppet (spring-loaded check) inside the valve body, allowing water to pass through freely.

2. Stopping Flow/Reverse Flow: When the forward flow stops, or if pressure downstream becomes higher than the upstream pressure (creating backpressure), the mechanism inside the valve automatically closes. Gravity or a spring assists in sealing the valve shut, effectively blocking any water from flowing backward. In backsiphonage conditions (where upstream pressure drops significantly), the lack of forward pressure also allows the valve to close, preventing contaminated water from being siphoned back.

The Role of Check Valves in Backflow Prevention Systems

While a single check valve offers basic protection, they are most often found as critical components within more complex and reliable backflow prevention assemblies. Devices like:

• Double Check Valve Assemblies (DCVA): These contain two independently acting check valves in series. This redundancy significantly increases reliability. If one check valve fails or leaks slightly, the second one provides backup protection.

• Reduced Pressure Zone Assemblies (RPZ): Considered the highest level of mechanical protection, RPZs also use two independently acting check valves, but they add a hydraulically dependent differential relief valve in between. The check valves are the primary means of stopping reverse flow here too.

In these assemblies, the check valves are the workhorses that physically block the reverse flow of water during backpressure or backsiphonage events. Their reliable closure under adverse conditions is essential for the entire assembly to function correctly and protect the potable water supply from potential contamination.

Why They Matter

Understanding check valves highlights their importance in maintaining water safety. They are fundamental building blocks within the crucial backflow prevention systems that safeguard public health.

Ensuring these assemblies, including their internal check valves, are properly installed, tested, and maintained according to local regulations is vital for preventing contamination events and keeping our drinking water safe.