Going With the Flow

“The cross-connection is the point where two systems interconnect,” says Rick Fields, director of sales and marketing for Zurn/ Wilkins, Paso Robles, California. “For example: you have the water supply, and the irrigation system. At the point where these two systems join is where contaminants may enter the drinking supply, and this is known as a cross connection.”

There are two types of cross-connection, direct and indirect. “If I am installing an irrigation system and I hook it to the water supply (main), that is a direct cross connection,” says Fields. “A garden hose, however, is an example of an indirect cross connection. Normally it isn’t a risk, but it can be if left in a puddle of muddy water, a swimming pool, or some kind of herbicide or chemical spraying apparatus.”

Backpressure and backsiphonage can occur separately, or they may occur at the same time. Backflow prevention devices are built to handle one or both of these conditions. Backsiphonage is the most common type of backflow. The unwanted reverse flow of water can be caused by many problems, but the most common culprit is due to a loss of pressure in the supply main. This creates suction back to the main, causing backsiphonage.

“Back pressure can be caused by a pump located downstream of the device,” says Fields. “The most common type of backpressure in an irrigation system is caused simply by an elevation change. If I take a pipe and run it uphill, the elevation will cause an increase in backpressure. Or, it can be caused at the cross-connection at the customer’s pressurized system. When the pressure at the supply point becomes lower than where the water exits, backflow will most likely occur.

“Backpressure is caused by a greater pressure originating in the irrigation system that can overcome the drinking water system supply pressure, causing a reverse flow condition,” says Mike Gaulin, marketing manager for Watts Industries, North Andover, Massachusetts.

A backflow prevention assembly fixes this problem, but the right one must be used. This is based chiefly on particular hydraulic conditions, such as pounds per square inch (psi) and flow rate. Additionally, as more municipalities establish specifications, certain devices may be mandated and may differ from county to county.

“When in doubt, the best call you can make is to the local water authority,” says Bruce Parrott, national sales manager of backflow products for Watts. “They will tell you if a backflow prevention device is necessary, and which type to use.”

Each property/system has its own degree of hazard that determines the system’s risk to the potable water supply, and how dangerous a backflow condition may be. It also plays a role in the consideration of what kind of device to best install.

The level of hazard is determined by the kind of substance that may enter the water supply. A pollutant is considered to be any substance that can affect the color or odor of the water, but would not pose a health hazard. This is referred to as a non-health hazard. A contaminant, however, is considered to be any substance that can cause illness or death if ingested. Pesticides used on many residential and commercial properties fall into this category.

“Some properties may have chemicals and fertilizers being injected with the irrigation. This would obviously make the hazard level higher,” says John Brewer, vice president of sales at SPX, Charlotte, North Carolina. “So the scale of water hazard can fluctuate, and the right kind of device must be used to compensate.”

An irrigation system is considered to carry a high hazard risk, with the chance for contaminants to infect the drinking water, due to the use of pesticides and fertilizer. When you determine the hazard of a property and the risk of backflow, the selection of a specific device gets a little more complicated. “You would look at the degree of hazard, and check with the local jurisdiction to find out what devices they recommend,” says Doug Deviney, national sales manager for Conbraco Industries, Matthews, North Carolina. “But then you have to see if the particular device is not only proficient at stopping the backflow, but is also practical.”

For example, he explains, one type of device that can be used to control backflow is a pressure vacuum breaker. It protects primarily against backsiphonage. The valve is designed to be installed in a continuous pressure system 12 inches above the overflow level of the system. It must be installed a minimum of 12 inches above the highest point in the sprinkler system.

It sounds easy enough, except if the property in question is a large area, maybe a golf course or a commercial installation. If the sprinkler system extends up hills, it might require you to install this device higher at the inlet than would be practical. Remember, this has to be installed 12 inches above the highest point of the irrigation system, so you might end up having to put this valve twenty feet high. Obviously, this option would be absurd, and therefore, not a practical solution for this kind of installation.

The difference between a residential installation and a commercial installation usually comes down to the size of the device, and how large the valve is going to be. “Flow rate and pressure loss determine

the size of backpressure prevention devices. All manufacturers will provide pressure loss curves in terms of psi. As you try to push more water through a valve, you will have more pressure loss, which calls for a particular size of device,” says Deviney. “In most cases, the municipality will have codes to determine what kind of device you must use; you, the contractor determine the size,”

So, here is a plan of action to help you decide what kind of backflow situation you may have. It is recommended by many in the industry to first establish what kind of cross-connection is at risk. Then, assess the hazard, and determine whether the risk is “high” or “low”. The third step is determining whether the system is under continuous back pressure or noncontinuous.

“For a non-continuous situation, the valve will see 12 hours or less of continuous pressure,” says Fields. “If I turn on a line, and turn it off, eliminating the water pressure in the backflow preventer, it was noncontinuous. But for a situation where there is a constant stream of pressure over 12 hours in a 24-hour time frame, such as an irrigation system, it is a continuous pressure application.”

The next set of criteria is the type of backflow the valve will be subject to. This involves the aforementioned concept of backsiphonage and/or backflow. Then, there is the consideration of specific flow rate and pressure losses in a system.

There are many different backflow prevention assemblies. Here are four of the most common setups for irrigation applications.

Atmospheric vacuum breaker

This is composed of a single float and disc with an atmospheric port. This set-up will handle high hazard cross connections that are not subjected to continuous pressure. They have to be installed six inches above the highest sprinkler head, and are used to protect against backsiphonage only. If you are installing these on a system with multiple zones, you’ll have to use one for each zone.

Pressure vacuum breaker

Composed of a spring-loaded float and disk with an independent check, this device is also supplied with shutoff valves and ball-type test cocks. It must be installed 12 inches above the highest sprinkler head, or the highest point of the system. Basically, if you are on site with any kind of sloping terrain, this is probably not your best option. Designed to protect against backsiphonage, it does not work with backpressure. It is designed for health hazard installations.

Double check valve assembly

It contains two independent check valves, and the checks are replaceable for repair and testing. These are for non-health hazard cross connections, and continuous pressure applications. The check valves are replaceable for repair and testing, and they can handle both backsiphonage and backpressure. This type of assembly is usually mounted inside a meter box underground, so it is more aesthetically appealing.

Reduced pressure backflow assembly

Built with two independent check valves with intermediate pressure differential relief valve, shutoff valves, and ball-type test cocks, this is considered by many to be the Cadillac of backflow prevention devices, especially in regards to irrigation. It will protect against backpressure or backsiphonage, and is designed for high hazard installations. It is built for continuous pressure applications, and affords the highest degree of protection for the water supply. It needs to be installed above ground. “If you don’t know what the local requirements or laws concerning a backflow device in any given municipality, you really can’t go wrong with a reduced pressure backflow assembly,” says Parrott. “It may be overkill in some situations, but it affords great protection.”

It is recommended that all of these assemblies, with the exception of double check valve assemblies, be installed above ground. Usually, the local water authority requires that they be installed 12 inches above the ground, and located far enough away from the building or structure to allow for maintenance and repairs. Also, be sure that they are located in a place where they will not cause water damage should they discharge, which some models will as a final safety mechanism should one of the check valves fail.

“I saw one house where they had a backflow assembly in a fully furnished basement,” relates Parrott. “It isn’t a matter of if it will happen, it’s simply a matter of when—eventually something will stick in the valve and water will drip or flow out of the assembly. There will be some serious water damage in that basement.”

As aforementioned, regulations concerning backflow prevention devices fluctuate between cities and municipalities, so there isn’t an across-the-board policy when it comes to residential and commercial set-ups. Commercial installations are usually under more scrutiny, and most are required to undergo yearly inspections and tests. However, many water authorities do not require annual testing. Professionals say it’s a good idea to test them anyway.

“As a manufacturer, we strongly recommend that all backflow assemblies, regardless the type, be tested annually,” says Parrott. “Since the irrigation contractor is at a property anyway, he could offer testing of the assembly as an additional service as part of his winterization or spring start-up program. The testers usually must be certified, but there are classes all over the place for that; most are about 40-hour courses.”

Because of the health risks that backflow can pose, it is crucial to be diligent about using the correct backflow device, and periodically maintaining and testing it. For any project, make sure you call the local authority for guidelines, and ensure that the protection is enough for the threat. Your liability may be at stake, and your city’s drinking water may depend on it.

Enclosures
     Aesthetically, backflow assemblies aren’t exactly the most graceful things to the eye. A concoction of pipe jutting from the ground isn’t very appealing, but enclosures can help soften the look. Backflow prevention devices are expensive; and it makes sense to protect them from being vandalized, in some cases these enclosures will also protect the devices from the elements as well.
     Besides aesthetics, vandalism is a major cause of concern. It is very easy for vandals to turn the ball valves off, tamper with the assembly, and possibly damaging the unit or the property that the assembly is protecting. There is even the threat of someone stealing the entire assembly itself.
     “What these enclosures will do is help ease the eyesore that these assemblies can become in front of a nicely manicured lawn or building,” says Jeff Keim, owner of Backflow Prevention Device Innclosures, Phoenix , Arizona . “It will help it look much better than it being out there, or in a rusted out case in front of a property.”
     Many are made of expanded metal, either molded into rectangular iron cages or into a rounded pipe frame. “For looks and rust prevention, it’s a good idea to make sure the enclosure is powder coated or has some kind of high quality finish,” advises Keim.
     “Security is an extremely important issue when considering an enclosure, especially for a backflow prevention device,” says Doug Moore, marketing manager for VIT Strongbox, Escondido, California. “In most cases, contractors are responsible for the condition of the landscape. Someone tinkering with the assembly can damage that landscape real fast.”
     So, ensuring that these enclosures are lockable is a must. Most can be secured by a padlock, but in some cases, contractors feel more comfortable with an added level of security. “Some contractors put a steel box or bracket around the padlock so bolt cutters won’t work,” said Keim.
     Having the enclosures that you install keyed alike might help alleviate issues down the road. Members of your personnel can access all of your customers’ enclosures by using one key, and making additional copies won’t be too much of a hassle.
     In some parts of the country where temperatures have a nasty habit of dipping low enough to freeze a backflow protection assembly, certain enclosures can be had to help safeguard against cold snaps.
     “You can get a solid sheet metal enclosure and insulate it, or a fiberglass box,” says Keim. “On top of that, you can wrap the assembly in an insulating blanket. This is basically cold snap insurance. I know many people who use them in Colorado and have had good results with them.”
     Moore emphasizes the need for enclosure durability. “The odds are this thing is going to get wet,” Moore says. “If it isn’t fabricated from stainless steel, aluminum, or doesn’t have rust thwarting properties, it will not hold up.”
     Here are a few tips: You can save yourself future headaches by thinking ahead and allowing enough room for an enclosure to be installed. Sometimes the owners are reluctant to pay for an enclosure when the device is installed. However, down the road, either because of vandalism or asthetics, when an enclosure is required, you’ve allowed enough room for it. “For areas that are more cramped, but which still requires an enclosure and access to the assembly, there are units that can be easily removed without tools,” says Moore.
     Backflow prevention devices are often expensive but are necessary to protect the water supply. Vandalism and weather can effectively change that. Enclosures are simply a smart and easy way to keep this investment safe.