What is a backflow preventer? Well… plumbing is great, isn’t it? You turn on a faucet and clean water comes out, then you pull the plug and the dirty water flows away. Simple. Well, it turns out that there’s actually a good deal of clever engineering involved in keeping it that way. One area of particular concern is avoiding clean and dirty water mixing, otherwise known as backflow.
Understanding Backflow
Backflow is the term that describes a clean water line being contaminated by dirty water flowing in the wrong direction.
This results in the mixing of clean and dirty water within the system. Not only does this present serious health risks, it can physically damage your plumbing and appliances.
There are two mechanisms which can cause this unsanitary problem; back pressure and back siphonage.
Back Pressure
Water pressure is a core concept to how your plumbing works. The pressure within your pipes is what carries the fresh, clean water around your home. When the pressure in the waste system is higher than that in the supply system, water will be pushed the wrong way, contaminating the supply.
Causes
Common causes of back pressure include:
- Pump failure
- Problems with pressurized systems such as boilers and sprinklers
- Problems with sewer lines
Back Siphonage
Back siphonage occurs when there is negative pressure in the supply. Nature abhors a vacuum, so negative pressure will draw water from the waste line to equalize itself. The result is that contaminated waste is pulled into the clean water line.
Causes
Common causes of back siphonage include:
- Breakages in water mains
- Heavy demand
What Is A Backflow Preventer?
So, now that we know why they’re needed, what is a backflow preventer exactly?
Put most simply, a backflow preventer is any feature of a plumbing system which is designed to prevent contamination via backflow. There are a few common devices which can be installed along a plumbing system to avoid this problem, ranging from air gaps to complex constructions involving multiple valves.
Regardless of which model is installed, the aim is the same: ensure that water can only flow in one direction. The exact mechanism varies from relieving vacuums to normalize pressure to physically blocking water from flowing backwards.
The most common are:
Air Gaps
These are almost ubiquitous in any home with a modern dishwasher. If you look under your kitchen sink, you’ll probably find one there. They provide, as the name suggests, a literal gap between the outlet and flood level, separating the two hoses.
They prevent your dishwasher from flooding with contaminated water and avoid debris finding its way back into it. Older systems may use a “high loop” which uses gravity to prevent contamination, though this is less effective.
Double Check valves
Double check valves exist to ensure that water can only flow in one direction. They work by opening when pressure is higher on the incoming side and closing when it’s higher on the outgoing side. This creates a physical barrier to stop water being pulled upwards from the waste and back into your home.
They can be installed either where your home’s plumbing meets the sewer line or at each outlet, such as sinks, baths and showers. They’re generally best installed on a horizontal length of pipe to stop gravity interfering with their mechanisms.
Atmospheric Vacuum Breakers
Atmospheric vacuum breakers can be found in hoses and faucets around your home. When the system loses pressure, a check valve opens and breaks the vacuum, sealing off the water supply.
They’re not effective in a constant pressure system and can’t be placed upstream from a shut-off valve. They’re also susceptible to atmospheric contamination as they’ll draw anything in the air into your plumbing. This makes their usage rather limited.
Reduced Pressure Zone Assemblies
Reduced pressure zone assemblies are more common in commercial settings and as part of the municipal supply, but some systems in the home may require one. They consist of two double-check valves and a relief valve that opens if both happen to fail.
If the relief valve is leaking, you know something has gone wrong, but at least it’s not entering your drinking water.
Importance of Backflow Preventers
Regardless of which type may be installed, backflow preventers are vital for the protection of public health. All sorts of diseases can be spread when potable and waste water are mixed. This is the reason that most state’s plumbing codes require them to be installed and many local municipalities have even tighter regulations.
The American Society of Sanitary Engineering set a national set of standards, covering a wide variety of applications. These standards should be adhered to by any professional plumber when installing a system.
Common Applications Of Backflow Preventers
Water backflow prevention devices are commonly found around the home and in commercial settings. Anywhere where waste and fresh waterlines may cross should have some device installed. The most common locations are in:
- Sprinkler systems
- Outdoor hose bibs
- Swimming pools
- Septic tanks
- Sewer connections
- Irrigation systems
More complex assemblies may be found in places where the risk of contamination or the potential effect on public health is greater. These might include places that prepare food, hospitals or manufacturing or agricultural institutions. In settings such as these, it’s not uncommon for there to be multiple systems at play. This allows for a continuous water supply, even when something has gone wrong with one.
You’ll also find backflow preventers on a grand scale in the municipal water supply and sewerage systems. These are in place to protect public health and ensure that there’s no risk of cross-contamination. Many sewers and public water supplies will feature reduced pressure zones or assemblies involving multiple check-valves. These are particularly useful as they offer a certain level of redundancy and extra protection for the public.
Installation and Maintenance Of Backflow Preventers
The installation and maintenance of anything designed to prevent backflow is best left to the professionals. This will ensure that the right device is chosen for the job and everything is up to code. With the risk of contamination of potable water and the impact of this on public health, saving a few dollars just isn’t worth the risk of getting it wrong.
As with any mechanical device, maintenance is a must. Even the simplest systems will wear out eventually. To ensure that everything is working as intended, it’s best to schedule an annual examination.
During an inspection, your plumber should switch off the water supply, leaving some in the pipes to avoid the pressure dropping entirely. They may use a variety of tests and tools, depending on the exact specifications of your system, to ensure that everything is working as it should and water is only flowing in one direction. They’ll check things like the pressure within your valves and let you know what needs doing.
When Something Goes Wrong
Needless to say, when you suspect a problem with your water backflow prevention devices, you should call a plumber as soon as possible. Potential causes for concern include:
- Drops in water pressure in your boiler
- Leaks
Choosing the Right Backflow Preventer For Your Needs
With so many different varieties of water backflow prevention devices out there, it’s important to know you’re installing the right one. Consulting with a professional plumber will ensure that you’re protected and up to code. They’ll take into account your specific needs before making a suggestion which meets all the required regulations.
While there are cost differences between different types of devices (generally, the more complex, the more expensive) the peace of mind that each brings make them worth the cost. It’s also worth considering your backflow preventers as more of an investment than a cost. When properly installed and functioning, they serve an important purpose in protecting your appliances and plumbing. They also protect your health and that of the public at large and you can’t really put a price on that!
That being said, installing an RPZ when a normal double-check valve would be more suitable would be overkill. Your installer will be able to keep you right and ensure that you’re meeting your needs while avoiding overspending.
In Conclusion
So, what is a backflow preventer? It’s a vital part of any plumbing system, serving to protect your drinking water from your waste. They play an important role in public and private settings and anywhere where there’s a risk of contamination. As such, there are complex rules and regulations imposed by both state and local authorities and these are regularly reviewed and updated.
If you’re planning on installing a new plumbing system or updating an old one, it’s worth consulting with a pro before you get started. They’ll keep you right and your water flowing the right way.