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Backflow Prevention

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What would you do if you got up one morning, went to brush your teeth and saw yellow gushy stuff pouring from the faucet? Residents in Woodsboro, Maryland, awoke to just this scenario, with gunk spewing out of faucets and spigots all over town. Town officials quickly banned water use and began an investigation. After flushing the water system, the investigation revealed that a powerful agricultural herbicide had made its way into the town’s water system.

In another incident, a man from Georgia ended up burning nearly 80 percent of his skin off from the water in his shower. He lived near a soda plant, which had experienced problems with backflow, causing caustic water to make its way through the city mains.

Because of mishaps such as these, and to comply with the federal Safe Drinking Water Act, most cities, states and municipalities have made backflow prevention devices mandatory. If the building code calls for it, the landscape contractor has both a legal and moral obligation to install backflow preventers and to make sure they are installed correctly. These devices play a key role in keeping our drinking water safe.

It is important to understand what these devices do and why they are necessary. If you understand this, you will be able to ensure that the projects you’re involved with comply with local codes and keep the drinking water safe. Unfortunately, backflow and backflow prevention is not well understood.

“As an industry, we have failed to educate the average landscape contractor on what backflow is and what the dangers are,” says John Brewer of Bailey Water Products. Understanding backflow prevention is truly more than half the battle.

Correctly installed and maintained, backflow devices provide a relatively cheap way to prevent instances like the ones cited above from happening.

The main idea is this: water purveyors want to deliver water to your property, but they don’t want it back, and neither do you. After the water passes onto your property, it can pick up all kinds of contaminants from dirt to animal feces. If this water is permitted to re-enter the potable supply, it can be dangerous.

So what is backflow?

Back flow is best described as a flowing back or reversal of the normal direction of water from homes and buildings, leading to the possible contamination of potable water systems. Backflow can occur at points known as cross-connections. Cross-connections are generally defined as any physical connection between the piping system from the water company’s service and that of any other pipeline utilizing this water for human or industrial consumption .

Once the water leaves the company’s service lines, the potential for pollution and contamination can create water that is not, or cannot be, approved for human consumption.

There are two forms of backflow: backsiphonage and backpressure.

Backsiphonage can be caused by supply leaks in the distribution system or other high withdrawals of water from the system that lowers the water pressure to the point that a vacuum is created in the pipe. This vacuum can then draw used water or other contaminants back into the public water supply system through open outlets, like sprinkler heads or hoses that might be submerged.

The other cause of backflow is backpressure, which occurs when a water user’s piping system creates a higher pressure than that in the public water system. This can be caused by pumps, thermal expansion or elevated piping. The increase in the system piping pressure will force contaminated water back into the main supply.

The first step, and perhaps the most crucial of all steps prior to installation, is to look up the local codes in your area.


Each state, city, county or municipality may have different laws and regulations regarding what type of device you can use and how it’s installed. For example, in California, you typically may not use a double-check assembly, whereas in Texas, you can. While there are reasons that govern some of the regulations, like those above, many regulations are similar.

Below are the usual minimum general standards:

Install in an accessible location for inspection and servicing.

Flush pipelines thoroughly prior to installing backflow prevention assemblies.

Protect the assembly from freezing by properly installing it in a utility building, backflow prevention enclosure or shelter and draining and blowing the system out in the winter months when it is not in use.

When located inside a building, the relief-valve port on a Reduced Pressure (RP) backflow preventer should be piped through an air gap to a drain to prevent water damage.

The device should not be installed in pits where any part of the device could become submerged in standing water.

The RP assembly should be installed a minimum of 12 inches above grade, while a double-check valve can be installed below grade.

A pressure vacuum breaker must be installed a minimum of 12 inches above all downstream piping.

Again, always find out who the local authority is that has jurisdiction over where you’re installing these devices. The authorities will help you comply with the laws and regulations in your area. In some cases, they can also test the backflow prevention device.

Before proceeding with the next step of installation, be sure to know what conditions the device will likely encounter. There are four main forces or hazards that your system may come upon: backpressure or backsiphonage and non-health or health hazards.

The first two consist of the two types of backflow, which are backpressure and backsiphonage.

Knowing which will most likely affect your system will help you in deciding on a prevention device. Different categories provide different types of protection, so it is important to understand what they are.

The other two consist of what level of hazards you might encounter. Figuring out whether you are looking at a non-health or health hazard situation will also help you formulate a plan for backflow prevention. A health hazard label is commonly applied to systems containing contaminants, whereas non-health hazard applies to those with pollutants.

Pollutants generally change the water color, odor or taste, while contaminants can cause illness and death. Making a decision on a backflow device based on these four aspects will yield you a properly performing system. (Note: Codes vary and can dictate usage of different products for the same application.

The codes must be reviewed to ensure proper compliance).

Once you’ve researched the regulations and conditions, it is then important to know what type of device to install.

Because of the variable conditions, it is imperative to understand how each backflow device works, so the best one can be chosen for any given set of hazards and conditions. Each one has different basic operating principals and guidelines, which gives the installer many options when putting in a backflow system.

“The ultimate method [of protection] is the air gap,” says Brewer.

The air gap is a physical separation between the end of a potable water supply pipeline and the receiving vessel. A simple example of this would be a space between a faucet head and the ground. The space between the two points ensures that no cross-contamination can take place. The separation between pipe and tank must be twice the diameter of the piping and no less than one inch. This method of backflow prevention is considered safe even in a high hazard situation.

The problem with the air gap is that you have to re-pressurize the system after you expose it to air, plus you can attract contamination along the way. For example, buildings that have water tanks on the roof are examples of air gaps; however, animals and contaminants can sometimes penetrate these, rendering the water un-drinkable.


A Reduced Pressure Principle Backflow Prevention Assembly (RP) contains two independently acting check valves with a pressure differential relief valve between them. These units also have two shutoff devices—one upstream and one downstream of the check valves. This assembly is approved for health hazard situations, backsiphonage and backpressure. It’s just like a double check, but with a relief valve.

The Double Check Valve Assembly consists of two independently acting check valves. These units also have two tightly closing shutoff valves located at each end of the devices. This assembly is approved for non-health hazard, backsiphonage and backpressure situations.


As water-use regulations become more and more stringent, knowing about backflow prevention is imperative.

A Pressure Vacuum Breaker (PVB) employs an independently acting, spring-loaded check valve and an air-inlet valve that opens to admit air when the pressure within the body of the device approaches atmospheric pressure. This assembly is approved for health hazard backsiphonage. The system is initially pressurized and can stay pressurized all day, which sets it apart from an atmospheric vacuum breaker, which can only be pressurized for 12 hours out of any 24-hour period.

An Atmospheric Vacuum Breaker (AVB) consists of a check valve and an air-inlet valve much like the PVB but without the spring assist on the poppet. This assembly is approved for health-hazard backsiphonage situations. The device must be mounted at least six inches higher than all downstream piping and outlets.

A combination of device features, conditions at the site, and local regulations will help you make the decision about what type of device to use. As water-use regulations become more and more stringent, knowing about backflow prevention is imperative.

In an industry where water is crucial, understanding what causes backflow and how to prevent it will ultimately make you a better, and more successful, contractor.

 
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