Beyond the basics: Air Gap Backflow Prevention Device

A couple months ago I put together a blog about educating your direct customers on what backflow is, and why it’s important to have their backflow devices tested annually.It was a basic write-up of what backflow is, but didn’t delve into the specifics of various backflow prevention devices. For larger businesses that have multiple backflow prevention devices, or just curious customers, you might want to be able to supply them with a break-down of the various types of backflow devices. For the next couple weeks we’ll be looking at some of the similarities and differences between cross-connection devices that are utilized today. Direct your more curious customers here, to look at a simple but broken down perspective of how the various backflow devices perform.

Today we’ll focus on Air Gap Backflow Prevention Devices

Bathtub faucet air gap
The everyday air gap: faucets!

An air gap prevention device is precisely what it sounds like. It creates a gap between two potential water sources with air.  This completely eliminates the option for water to back-siphonage–and it’s probably a lot more common in your every day life than you might think.

Consider this idea: If you are filling a small pool with water, you might hold the hose over the pool to fill it. In this scenario, the hose is above the pool edge. The edge of the hose never touches the edge of the pool water. If the hose were to be turned off during this, there is an air gap that would prevent any siphonage between the hose and pool water. However, if you were to place the hose into the pool, turn on the water, and walk away only to return to turn it off when the pool was full, there is a chance for back siphonage if the hose is turned off before being removed. The pressure of the water in the pool is much more than pressure in the hose, causing water to return back into the hose. There is simply no air gap in this situation.

Air gaps create a physical separation between the water supply and the vessel.

“Unlike other backflow assemblies, air gaps are a non-mechanical means of backflow prevention.

Depending on the installation location, air gap cross connection devices could be deemed the safest way to prevent any backflow. They are often paired with Reduced Pressure Zone Assemblies to further reduce any potential backflow. They can be installed vertically or horizontally–they aren’t picky! Generally, an air gap must be at least twice the distance as the diameter of the pipe. In my pool example, a typical garden hose would need to be 1 to 1-and-a-half inches above the highest point that the water could reach.

Where are air gaps typically used?

Each state is different in how air gaps are tested. Some states mandate that nearly all backflow prevention devices be dependent on an air gap.

Air gaps are common for things like dishwashers–the air gap allows the water exiting the dishwasher to not be siphoned back in. The dirty water is pumped out of the dishwasher never to return. Clogged air gaps in dishwashers are semi common. It’s essential to fix this, and pretty easy to do.  You can often identify if your dishwasher has an air gap if you have a small air gap fitting in your sink–with little vents in the side.

Because air gaps interrupt pipe structure, they are primarily used at the end of a line where storage tanks, bathtubs, sinks, pools, and so on, are located.

So, is there any place that an air gap isn’t efficient? There are risks for an air gap not working entirely well in places like basements that could theoretically flood. Above ground though, an air gap is the oldest and most approved way of preventing backflow.

Next Monday I’ll check back in with a breakdown of how and where Reduced Pressure Zone Assemblies are used.

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Beyond the basics: Air Gap Backflow Prevention Device

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