As plumbers, we are required to protect water infrastructure and the end-users who rely on it. Cross connections pose a threat to these core goals, making it crucial for devices and appliances to have a backflow converter to protect the water supply.
Let’s start by defining what a cross connection truly is. The definition may not be worded exactly from one plumbing code to another, but the principle desired is the same. This is from the Wisconsin Uniform Plumbing Code. “A cross connection means a connection or potential connection between any part of a water supply system and another environment containing substances in a manner that, under any circumstances, would allow the substance to enter the water supply system by means of back siphonage or back pressure.”
Many fixtures have an integral backflow preventer, but we have to make sure it’s adequate for the job we are using it for.
Understanding and preventing a cross connection may be the single most important part of our code. Over a million lives are lost each year by consuming unsafe water worldwide. I feel like plumbers want to install the correct backflow preventers. Why are there so many cross connections? How many cross connections are out there that we don’t even know about since they haven’t hurt or killed anyone, yet?
I have a couple of thoughts. My first thoughts are that not every backflow preventer is created equal, this is on purpose. Now that’s not a negative toward any manufacturer or ASSE standard. Each of those do a great job. It would not be cost-effective to have one backflow preventer serve every backflow situation. It would be overkill for certain installs, and many may not install a backflow preventer because of the increased cost. This may create confusion in the plumber’s ability to make a correct decision on what backflow preventer is the best for a specific install.
WHAT TO KNOW
There are a couple of things that we need to know before choosing the correct backflow preventer.
What classification does it need? Now there are two separate classifications, high hazard and low hazard. If you are just guessing between the two, then always make it a high hazard classification. However, I don’t think we should be guessing. Since we have to think about the “potential” for a cross connection we have to think about after we leave how could someone else use it. That to me means anything that you could hook a hose up to needs to automatically be a high hazard situation.
What could they be using the hose for? Any install that connects to the drain system or has a connection with any other than potable water needs to be a high hazard.
If it deals with a chemical, what is the toxicity of the chemical? This is very hard since we probably are not versed in chemistry. We may need to email the manufacturer and ask them!
Back pressure or back siphonage? What’s the difference? In a generic answer back pressure has a positive pressure pushing back into the water supply. Not every fixture, device or appliance has something that may create an increased pressure pushing back into the water supply system. The three big examples of something that creates back pressure are: heat (thermal expansion), elevation, and equipment such as a pump. Back siphonage has a negative pressure pulling from the water supply system. That means every fixture, device or appliance that has water supplied to it can have the water “pulled back” into the water supply. This can happen with a water main break or a fire and the fire trucks connect to the nearest fire hydrants creating a lower pressure available in the water main. Water seeks to be a similar pressure.
The next thing to consider is does the backflow preventer have a continuous water pressure supplying what it is protecting? What exactly does continuous mean? A continuous situation is constant supply of water pressure for more than 12 continuous hours at a time. This may be the most overlooked and misunderstood part of backflow protection. I’ll give you a quick example: A flushometer serving a water closet has a continuous supply of water to serve the water closet. However, the ASSE 1037 that is protecting the water supply is downstream of the valve and only has pressure against it during a flush, not for more than 12 hours.
Why does it even matter if you have pressure for more than 12 hours? Well if it was only 13 hours realistically it may not, but what about the backflow preventer having pressure for years against it? I usually explain it this way, an atmospheric vacuum breaker, ASSE 1001 is only good for a noncontinuous situation. It has a small valve that when water flows through it closes off the opening to the atmosphere. The requirement for this being noncontinuous makes sure that the valve has potential to open and close every day.
Now we all know that water qualities can change drastically from one area to another and if we had some very hard water it could have the valve “stick” to the top keeping the atmospheric vent from ever opening, breaking the vacuum and protecting the water supply.
THINK ABOUT A CLASS
My intention of writing this article is just to have you think a little deeper before you install your next backflow preventer.
If your license requires some type of continuing education, consider a backflow prevention class.
------------
Ken Dickerson teaches plumbing apprenticeship at Waukesha County Technical College. He is the 2022 Associated Builders and Contractors of Wisconsin Instructor of the Year, a U.S. Air Force veteran and proud husband and father of two. To reach Dickerson, email editor@plumbermag.com.
