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Backflow Prevention & Enclosures for Irrigation Systems

Phillip Meeks | Backflow

With each passing year, additional criteria are tacked onto the definition of environmental responsibility. Maybe this year it’s the reduction of aerosol, and next year “greenness” is directly proportional to how much money was donated to the Save the Walrus Foundation. But one constant over the years has been water quality. Industries that negatively impact water quality are labeled as bad guys, plain and simple. Without clean drinking water, communities can’t grow and the health of all living things is compromised. So, when it comes to irrigation, the protection of a community’s potable water will always be a concern.

Irrigation systems are considered high-risk when it comes to the possibility of potable water contamination. Sprinkler heads and other components can allow contaminants like fertilizers, pesticides or pet feces into water supplies, and therefore, backflow prevention devices are used to eliminate such hazards. However, codes for installing and maintaining these devices are in a constant state of evolution, and what’s acceptable in one part of the country won’t be permitted in the next state over. Likewise, today’s acceptable standards for your region can change relatively quickly.

Handling with care
“The most important thing to remember,” says Jay Gray, an irrigation specialist with Environmental Care in Fullerton, California, “is that there are specifications and legal codes that need to be followed when installing or maintaining a backflow prevention device. If you install a device incorrectly, it will not do the job it was intended to do and could result in (1) liability, if someone gets ill or worse, (2) poor performance of your newly installed irrigation system or (3) damage to a backflow preventer if you disconnect or alter anything.”

A contractor can’t simply install the most inexpensive backflow prevention device and hope for the best. Rather, local codes and other factors must be considered, and individual situations will dictate which type of assembly will work best. It’s important to be careful when selecting a backflow assembly that will ensure you’ll have an adequate level of protection.

Anson Beattie, an irrigation specialist in Santa Ana, California, also with Environmental Care, says, “In regards to irrigation, you basically have four choices of backflow protection:
• Air Gap — useful applications in agriculture and golf courses. Air gap must be two times pipe diameter and never less than one inch;
• Atmospheric Vacuum Breaker (AVB) — typically seen in residential applications. Each valve has an AVB downstream of the shutoff valve. Needs to be installed a minimum of six inches above all downstream piping and outlets. No shutoff valve is allowed downstream of an AVB and an AVB cannot be used more than 12 out of any 24-hour period.
• Pressure Vacuum Breaker (PVB) — typically seen on small commercial projects. PVBs can be utilized under constant pressure. PVB must be installed 12 inches above all downstream piping and outlets.
• Reduced Pressure Principle Assembly (RPP) — basically the standard for most modern irrigation systems. Can be utilized under constant pressure. RPPA can be at a lower elevation than downstream components. RPPA needs to be set 12 inches above grade and have proper drainage.”

Jeff Keim, president of Backflow Prevention Device InnClosures (BPDI) in Phoenix, Arizona, offers this insight into the various devices: “It’s real common to use PVBs on landscapes, and a lot of times, that is suitable. But there are times when you can’t use those and you have to go to an RPP. A pressure vacuum breaker basically has to be a stand-alone system. You can’t have two or more units looped together. You can’t have two or more supply lines coming into a system that’s being protected by pressure vacuum breakers. They just won’t work against back pressure. They only work against back siphonage.”

However, Keim explains, the PVB is still a good system and one allowed by most jurisdictions, but a good rule of thumb is that, if you anticipate any type of back pressure, go with an RPP.
In some parts of the country, such as in the South, another type of backflow preventer is still allowed: the double check. A double check involves two spring-loaded check assemblies, and because these are situated in pits or meter boxes, they often serve as easy remedies to occasional freezing. However, double checks are less than ideal for a majority of landscape irrigation applications. “I would strongly recommend to any landscape contractor that they don’t put that in just because it’s legal,” Keim says. “The problem with a double check is it’s rated only for low-hazard usage, and when you talk about a lawn sprinkler system, it’s always considered a high-hazard cross-connection.”

Being underground, the pits that hold double checks could conceivably flood, and then everything could be siphoned back into the potable water supply. RPPs and PVBs, on the other hand, will be above ground in order to vent water.

However, there are those who disagree on the inadequacy of double checks. Paul Baker, an irrigation designer and contractor with Oasis Irrigation in Saint Simons Island, Georgia, says, “An approved double-check valve assembly (DCA) should be adequate, if the system is not equipped to inject chemicals. The DCA should be inspected by a qualified inspector on installation and annually thereafter.” Baker adds, “There are people who feel that a DCA is not sufficient protection for the hazards of irrigation systems. The odds of chemicals being applied, both checks failing, the automatic or manual valve being in the ‘on’ position and a vacuum being created by whatever means, all at the same time — let’s get real: it ain’t gonna happen.”

Features to consider
Once a contractor opts to go with a particular type of assembly, he or she has to then determine the types of product features that will best serve a client’s needs, and meet all legal requirements. For example, the integration of multiple components into backflow prevention assembly installations can simplify things a great deal for the contractor. This is illustrated in the Wilkins Preset, which comes complete with a strainer, a backflow preventer and a pressure regulator, configurable to the situation.

Since local health departments or water agencies often require yearly testing of backflow prevention, the industry has responded with built-in test fittings. This is another feature to consider if regular testing is apt to become burdensome.

Fields explains that the advent of a union-type ball valve connection today allows easy removal of the backflow prevention device in the case of winterization. “What people have had to do in the past,” says Fields, “is they had to basically remove the components of the backflow preventer and then drain the water out completely.” The ball valve union, by contrast, allows the contractor to break the unions apart, remove the backflow device and then cap off the pipe ends.

About enclosures
As a greater number of state regulations have required backflow preventers to be above-ground, the risk to these devices has increased. Vandalism and freezing are two of the most common factors in backflow prevention assembly damage, and two that can be thwarted relatively easily with enclosures.

V.I.T. Products, manufacturers of the Strong Box enclosure, is a proponent of metal enclosures for a couple of reasons. The first is longevity. They report that some enclosures have been in the ground for 12 to 15 years. Secondly, metal enclosures look good in the environment and create a “chameleon effect,” says Karen Moore of Strong Box. While these enclosures are constructed of 100 percent stainless steel, metal enclosures are evolving toward aluminum, simply because of weight issues.

Insulated enclosures may be a good idea, depending on your locale’s tendency for hard freezing, but insulated blankets are also available that fit beneath an exposed enclosure. BPDI’s FrostGuard Blanket is one example.

Other features to look for in any enclosure might include the locking system, door seals, crossflow ventilation and filtering against debris. Some enclosure companies also offer pre-fabricated enclosure pads to eliminate the need for pouring concrete.

Predictions for coming years
Looking into a crystal ball, several trends are likely to influence backflow prevention devices in the foreseeable future. First of all, more jurisdictions are requiring RPPs if there’s chemigation or reclaimed water, and Keim foresees a continuation of this. “The RPP is the unit that’s going to become, I think, the standard,” he says, especially as the cost differences between RPPs and PVBs become less pronounced. (On average at the present time, an RPP will cost approximately two times as much as a PVB.) By the same token, he predicts a significant reduction in double checks and the required removal of double checks already in the ground — one more reason for contractors to strongly consider other types of assemblies.

Fields identifies several trends in backflow prevention assemblies, including a focus on smaller, lighter, more compact assemblies, as well as products designed with geographically-specific installation requirements in mind, such as freeze protection.

And of course, water quality will continue to be an issue. City and county governments are more aware than ever of backflow and other threats to drinking water supplies. Booming populations, especially in the West, mean that potable water infrastructures are pushed to the limit.

Therefore, it’s only natural to believe governments will protect these supplies wholeheartedly.
As mentioned, irrigation is a high risk to drinking water supplies, due to the potential for backflow. Fortunately, the contractor has many choices within his or her grasp to prevent this occurrence and thereby keep the irrigation industry as “green” as possible.

May 2002

 
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