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For potable water, life is a series of one-way streets. Safe drinking water depends on all “traffic” within a water system to move in the direction it’s supposed to. Fresh water flows one way. It isn’t supposed to turn around and travel in the other direction.
In a perfect world, water would always follow the rules. But in reality, there are several situations that can cause backflow, an unwanted reversal in the flow of liquids within a piping system. When this happens, any contaminants within the system can flow back toward the source of fresh water, mixing with drinking water and potentially contaminating the water supply.
Consider this example: A home irrigation system with below ground sprinklers is running as usual when a neighborhood water main is damaged during road construction. Suddenly, the pressure that keeps potable water flowing into the system is gone and the water flow changes directions. Water from the irrigation system flows backward taking with it any pesticides, fertilizer, or animal waste that it may have come in contact with. This contaminated water can then mix with the potable water supply potentially making the homeowner and his neighbors sick.
The danger of this kind of contamination exists wherever there is a “cross-connection” or link between potable and non-potable water. This is where backflow prevention comes in. Appropriate backflow prevention devices keep non-potable water from flowing backward toward a potable water source.
Because irrigation systems provide an opportunity for cross-connection, and because irrigation water is considered a contaminant (something that creates a health hazard) an approved backflow prevention device must be installed in every system. It’s critical for irrigation professionals to be educated on backflow prevention in order to protect the public and to protect themselves.
|Photo courtesy: Zurn-Wilkins|
“As irrigation professionals, we have a social responsibility to protect the potable water supply,” says Jim Frommer, owner of the Landscape Resource Group in San Diego, California. “Many contractors don’t completely understand what backflow prevention devices are for and don’t know how important they are.”
“Everyone who is involved with the potable water system has a tremendous responsibility to insure that the system is not contaminated from user sources,” agrees John Brewer, General Manager of FEBCO, based in Fresno, California. “Involvement with the backflow ‘community’ including local chapters of the American Backflow Prevention Association or local water purveyors will improve knowledge of product and installation requirements.
Understanding the various products and how they work in each situation can prevent serious accidents. “It’s very important when installing a landscape irrigation system to make sure to use the correct product in order to protect the water supply,” says Kris Munson, Product Manager for Watts Regulator Company, based in North Andover, Massachusetts. “In a worse case scenario, a cross connection can occur and make people sick or even cause deaths.”
In addition to their social responsibility, Rick Fields points out that contractors have a legal responsibility to prevent backflow incidents. “Contractors have a liability when they install an irrigation system,” says Fields, Vice President of Sales and Marketing for Wilkins Water Control Products, located in Paso Robles, California. “If a backflow incident were to occur, even if they didn’t cause the incident, if it can be shown that they haven’t installed a backflow prevention device according to code or according to instructions, they can be held liable.”
Brian Vinchesi, president of Irrigation Consulting in Pepperell, Massachusetts, notes that contractors should have a good understanding of backflow prevention even if they aren’t the ones doing the actual installation . “The person who installs a backflow prevention device is liable if it fails,” says Vinchesi. “In most states, backflow devices must be installed by a plumber. But if the plumber is your subcontractor, you can also be held liable.”
There are two main conditions that cause backflow: backpressure and back-siphonage.
• Back pressure occurs when a drinking water system is connected to another system operating at higher pressure. Backpressure can be caused by auxiliary pumps or boilers within the non-potable system. It can even be caused by elevation differences
• Backsiphonage is caused by a negative or reduced pressure in the supply line. This reduced pressure could be caused by situations like water main breaks (as in the example above), by an open fire hydrant, or even by planned water system maintenance.
|Photo courtesy: Zurn-Wilkins|
It’s very important to match the correct backflow prevention assembly to each situation. Consideration of several factors will determine which type should be used. Among these are the type of system, whether fertilizer or other chemicals will be injected, whether the system might be subject to back pressure, back-siphonage or both, whether the assembly will be under pressure at all times, and whether the device must be testable.
The most important factor to consider is local code. “Don’t make any assumptions about what you’re doing,” says Fields. “Sometimes contractors make the mistake of guessing at the correct product to use for a specific application and they guess wrong. For example, a contractor may work in two cities. ‘City A’ may require one type of valve for a specific situation. The contractor may find the same situation in ‘City B’ and install the same valve. But ‘City B’ may not accept this one. The contractor would then have to remove the valve and install a correct one.”
There are several systems used to prevent backflow. Here are some of the primary types along with related guidelines (These guidelines may vary according to codes in your area):
• Maintains a physical separation between potable water and non potable water systems
• The gap must be maintained at all times and must be a minimum of two times the diameter of the supply pipe
Atmospheric Vacuum Breaker (AVB)
• Designed to prevent back-siphonage but will not protect against backpressure
• One must be installed for each irrigation zone directly after the control valve
• No valves can be installed downstream of the AVB
• Must be installed at least 6”above the highest point of water in the zone it serves
• Should not be used in systems that introduce chemicals and fertilizers
• Should not be installed in a situation where it will be under continuous pressure for more than 12 hours in a 24 hour period
Pressure Vacuum Breaker Assembly (PVB)
• Effective against back-siphonage but not against back pressure.
• Must be installed a minimum of 12 inches above the highest point of water they serve
• One PVB can be installed on the mainline and serve the entire system
• There can be no pumps or backpressure on the downstream side
• Should not be used in a system that introduces chemicals and fertilizers
Double Check Valve Assembly (DCA)
• Protects against both backpressure and back-siphonage
• One DCVA can serve the whole system.
• Control valves can be located downstream
• Should not be used in a system that introduces chemicals and fertilizers
Reduced Pressure Backflow Assembly (RPBA)
• Protects against backpressure and back-siphonage
• Should always be the choice when applying fertilizers and chemicals through the irrigation system.
• Only one RPBA is required to serve the whole system
• Is installed upstream of all control valves
• Must be installed a minimum of 12 inches above ground level
No matter what type of backflow assembly you use, it should be inspected on a regular basis and should be installed with accessibility in mind. It should also be protected from vandalism and other sources of damage. Devices should be properly winterized in cold climates.
What NOT To Do
Choosing a product that compromises safety is of course the biggest mistake you can make when it comes to backflow prevention. Big errors include putting in a device that only protects against back-siphonage but not against backpressure when backpressure is present. Not using an RPBA in situations where fertilizer is injected is another big error.
While safety is the biggest concern, choosing a product that is unnecessarily cautious is also a mistake. “If you pick a more expensive product than you need to because you don’t understand which one is the best fit, your pricing will be less competitive,” says Vinchesi.
|Photo courtesy: Watts Regulator Company|
Munson agrees. “If you install an RP you’re not going to have a backflow problem but there’s a downside to choosing an RP if you don’t have to. While an RP is the safest, it also has the highest head loss. By installing one where you don’t need it, you may be giving up pressure unnecessarily and you might have to put in a booster pump or make other costly modifications to the system. More knowledge can help you and your customers have both a safe and cost effective system.”
Surprisingly, one of the most common mistakes contractors make is not installing backflow prevention devices according to the manufacturers’ directions. Instructions are specified in documentation that must be shipped in the box. Documentation must also be provided to the owner of the system.
Another dangerous mistake is taking matters into your own hands when you’re not supposed to. “In most states the contractor is only allowed to work from the backflow out,” says Vinchesi. “If you’re not supposed to deal with backflow prevention devices, don’t! The liability is too high.”
Whether or not you do the actual installations, it’s important for you and your employees to stay educated on this issue and remain up-to-date on changing technology. “The IA has excellent classes on this,” says Munson. “You can also talk to your local water authority. They’ll be able to take a look at your system and advise you on what’s adequate for what you want to do.”
Manufacturers provide an excellent source of education and support. “The irony is that manufacturers have all of these free classes, but many people don’t take advantage of them,” says Frommer. “I pay my people to go to school. It’s a requirement. They’re my biggest asset and it’s part of my responsibility to see that they’re educated on this.”
All irrigation contractors have a role to play in safeguarding the limited supply of drinking water. A thorough understanding of backflow prevention is one of the most important parts of that role.