What Is A Backflow Preventer?

A backflow preventer is one of the unsung heroes of our residential plumbing systems. These devices are crucial in preventing issues such as water contamination, sewage backups, or basement flooding. But what are they, and why are they so important? In this blog, we will get to the bottom of it!

What Causes Backflow?

To understand what a backflow preventer is, we must first understand what backflow is.

In the simplest terms, “backflow” is liquid or waste flowing in the incorrect direction in which the system was designed. This can happen on supply and drain lines and can occur for different reasons.

In pressured supply lines, things get a little more complicated. Water travels from a higher pressure to a lower pressure. This simple concept allows a city water department to distribute H2O to residential homes. Water is channeled through a main line at a high pressure, which branches off to individual houses, stepping down the pressure along the way.

But on certain rare occasions, the downstream water pressure may become higher than the pressure from the main, causing the water to change directions, also known as backflow. When the normal flow of water has reversed, serious issues can arise, as it can draw potentially contaminated water back into a potable water line. How do we avoid this issue? In the comes the backflow preventer!

What Is A Backflow Preventer?

A backflow preventer (or BFP) is a valve that has one simple function – allowing liquid to flow one direction, and stopping it from flowing in the opposite direction. There are several different types of these devices, and they are generally utilized in two main settings: irrigation systems and drainage systems.

Image sourced from: https://www.pacificbackflow.com

Backflow Preventers on Irrigation Systems

If you have a sprinkler system at home, you likely have a backflow preventer. Being that irrigation systems are often buried and exposed to outdoor elements, it is possible for contaminants such as chemicals or waste to find their way into the irrigation lines.

For instance, you may have pets that access your lawn to do their business. Or maybe you use fertilizer, pesticides or weed killer. Rain can wash all of these contaminants into the soil. And in the case where negative pressure pulls liquids back into your irrigation lines, you now all of a sudden have contaminated liquid traveling back toward your potable water supply. But, as you can guess, the backflow preventer will save the day! They are installed between your fresh water supply and the main irrigation line, effectively keeping the two lines separate.

These apparatuses are such an important safeguard, that Colorado building code requires them in most setups involving irrigation.

This diagram illustrates the double check style valve BFP, generally used on larger irrigation systems. Image sourced from: https://bethpagewater.com

During our standard inspections, we always test the sprinkler systems (when the season permits). While running the sprinklers, our inspectors make sure that BFPs are properly installed and free of any leaks, damage or defects. We usually come across Pressure Vacuum Breaker (PVB) backflow preventers, like the one shown below. This style of device is most commonly found in residential homes with smaller irrigation systems.

Note that, while we do conduct this general BFP inspection, we are not plumbing professionals. And it is recommended to have your backflow preventer tested annually by a qualified pro.

Pressure Vacuum Breaker (PVB) backflow preventer

Backflow Preventers on Drainage Systems

Backflow preventers in drainage pipes, also know as backwater valves, are constructed differently than ones used for irrigation. However, the same concept applies. Water can only travel one way. As the diagram below illustrates, this device can be installed seamlessly on the sewer line of a home. If water is flowing in the correct direction, the flap will remain in a downward position, allowing all waste and liquid to pass. However, if the flow reverses, the flap will float to its upward position, effectively obstructing any backflow of sewage.

Image sourced from: https://www.squareone.ca

These devices are especially effective in areas susceptible to flooding or below the municipal sewer main. In the case that a heavy rainfall occurs or there is a blockage in the municipal line, it will help to prevent any serious flooding from occurring in the basement of the home.

During our standard inspections, we are able to inspect these valves when they are readily available. Unfortunately, they are often under ground or connected to an outside sweep. However, if we can see it, we ask a few questions. Is the clean-out cap intact and in good condition? Is the area free of any visible leaks or damage?

During our sewer scope inspections, our inspectors are often able to see the BFP from within the pipe. We are not experts on these devices, but we will be sure to make note when they are present. If there is an access point before the device, our technicians are able to scope up the BF preventer. We can also inspect the line after the valve, if any accessible clean outs are available.

We, unfortunately, cannot scope through the valve as it can cause damage to our sewer scope camera and the valve. This can make scoping a line with a backflow preventer tricky as they aren’t always installed in the most ideal spot.

For more information about our sewer scope inspections, visit us online.

Conclusion

As you can see, backflow preventers are essential devices in both irrigation and drainage systems. They defend the clean water supply and protect buildings from water contamination and damage, making them a must in many household settings!

If you have any further questions about backflow preventers, don’t hesitate to reach out to us through our Ask Your Inspector program.

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