Backflow Devices 101: An Important Component of Modern Plumbing Systems

Backflow Devices 101:
An Important Component of Modern Plumbing Systems

Modern plumbing systems work so well that most people probably don’t think about what goes into bringing potable water to the sink. But stop for a second and consider the fact that, in one way or another, your tap water is connected to pipes that run to places like fertilized agriculture fields, chemical processing plants, and sewage systems. If any of those had a backflow occur, it could cause some pretty serious health problems. So what do modern plumbing systems use to keep your clean water clean?


They say an ounce of prevention is worth a pound of cure, and that’s exactly the philosophy behind backflow devices. Like most inventions, it was created to solve a problem. In this case, it was to address the possibility of contaminating the fresh, potable water supply at a cross-connection point. These cross-connection points are the location where potable water potentially can become contaminated.

The first known backflow devices came about in 1930, according to Safe-T-Cover. They were the product of an organization in the US called the American Society of Sanitary Engineering, or ASSE. With the motto of “Prevention rather than cure”, they set out to develop ways to improve and standardize plumbing systems – and cross-contamination backflow problems were a top priority.

By the 1950s, the double check valve became the main backflow prevention assembly. Then by the 1970s, the EPA was onboard with the Safe Drinking Water Act. Fast forward to today, and we have the modern systems that you’ve probably seen all over the place. The standards for these devices are continually improved and new models are in development all the time – all in an effort to make sure we get clean water when we need it. Check out Safe-T-Cover’s article to learn more about the history of backflow preventers.


It’s all in the name. Backflow devices, also known as backflow preventers, prevent backflows. To put it simply, they’re a valve that is held open by pressure from the water supply. When that pressure goes away, the valve closes to prevent water from flowing backwards. And there are only two things that could cause that.

Water is intended to flow in only one direction from the source to the building’s plumbing system. That’s accomplished by pressurizing the water at the source so that it’s higher than the pressure in a given building’s plumbing system. Physics takes over and brings you fresh water. But when the pressure is higher in the system than it is at the source, you get a backflow. The system is literally pushing water backward through the pipes.


The first way this happens is with back pressure. Back pressure is cause when the building system is actively creating pressure, pushing water out and back to the source. Think about a water pump used to pressurize water further down the line. When it kicks on, its job is to push water forward. But in doing so, it also creates a little bit of pressure in the opposite direction. That’s the back pressure.

If back pressure gets high enough that it overcomes the water supply, it causes a backflow and the check valves will close on the preventer. That matters because pressurized water is often used in irrigation, fire sprinklers, and industrial cleaning – all of which involve chemicals and metals that aren’t safe to consume. If any of them get into the system because, for example, the nozzle is left laying in a puddle of fertilizer runoff, back pressure could push that into the public water supply.


The other way a backflow is created is through back siphonage. You’ve probably heard of people siphoning gas to steal it out of cars, and the same physics principle can create a backflow. As water is pushed up into a building, gravity is trying to bring it back down. The pressure in the water supply is what keeps it flowing in the right direction.

However, there are certain times when that supply pressure drops. One common example is when the plumbing system in a new building is connected for the first time. While that building’s system is filled up, it takes pressure away from the surrounding area. if the surrounding buildings don’t have backflow devices installed, then the sudden drop in pressure would allow gravity to pull their water down and into the public supply effectively turning any hoses into giant straws. If they’re laying in any kind of contaminant, it gets sucked through the plumbing and suddenly the public water is carrying all kinds of nastiness.


Any licensed plumber can install one of these critical pieces of modern plumbing systems, but you must have a certified tester present during installation to make sure it’s working properly before putting it into service. It’s like going to a notary – they can’t verify it unless they’re present when it happens. Of course, this is only true for testable devices. But any of the ones you’d see installed at multi-family, industrial, or commercial buildings will be testable. So if you’re a Facilities Manager or Property Manager, odds are your portfolio includes buildings with these. All you need to do is keep a copy of the tester’s report handy in case it’s needed. Other than that, it’s the tester’s responsibility to file their report and results with the water district.

Once installed, these devices are always working. while it might seem like emergency equipment that’s only in use when there’s a problem, it’s actually the opposite. Since they’re designed to shut in the event of a backflow, that’s the only time they’re not operational. It’s a bit counterintuitive, but their primary function is actually to let water flow – but only in one direction.

The devices vary depending on the manufacturer and intended use, but in general all of them will have the same main components. They’ll all have a water line in, the check valve housing, the spring loaded check valves, testing ports, relief valves depending on the model, and finally the water line out. Since they’re all relatively the same, the maintenance on them is fairly routine.

Primarily, maintenance consists of annual testing to ensure that the device is in good working condition. If the device passes, it stays in use for another year unless a problem arises between tests. That’s usually indicated by leaking or discharge from the relief valve.

If it fails a test, or has a problem between tests, it usually triggers one of three types of repairs:

  1. Rubber repair – removing and replacing the rubber seals inside the device
  2. Full hardware repair – removing and replacing all of the moving components within the device
  3. Full replacement – completely removing and replacing the entire unit, including the housing

Occasionally, debris can be the cause of a failure and removing that debris or blockage will fix the device and allow it to function normally. But usually by opening the device to get to the debris, rubber seals are damaged and need to be replaced. So almost every time you service a backflow preventer, you’re going to be replacing something.


Speaking of replacement, another time these get replaced is when they’re stolen. many of these devices are made of up to 85% red brass, which thieves have realized is valuable. If they do decide to take yours, at a minimum you’re looking at expensive repair costs and a loss of water pressure in your building. If the thieves are sloppy with their work, it can cause backflows and create serious health risks.

Since crooks aren’t disappearing any time soon, many companies have come up with clever ways to deter or prevent theft of these devices. At the low end, there are valve guards that prevent thieves from shutting off water before they cut the device out. If they decide to cut anyway, they’re left soaking wet. Prevention options go all the way up to full metal enclosures that surround the entire device and bolt into concrete. Your plumber can help you determine what level of security is best for your situation.

So next time you see one of these, think about how important they are and thank your plumber and backflow tester for helping to keep your water clean and drinkable.

AAA Facility Services is a C-36 licensed commercial plumber with a backflow testing certification. Contact us today to request service.

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