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FLIPPING THROUGH THE notes on your upcoming landscape projects, you find a sticky note attached to the irrigation job scheduled for next week. The note reads, “Backflow device needed.” You remember hearing other contractors talk about cross-connection control and backflow devices, but you wonder what they are and why they are so important.
A reversal in the flow of water is called backflow. There are two types of backflow: backpressure backflow and backsiphonage backflow. Backpressure occurs when the pressure downstream increases over the system pressure and causes a reversal in the flow of water.
On the other hand, when the supply pressure drops, backsiphonage causes a reversal in the water flow. For example, a break in the main line in front of someone’s house drops the municipal water to 30psi. The homeowner’s irrigation system has 45psi. Because the irrigation system has a higher psi than the city water main, city water is sucked back into the irrigation system, explained Pete Chapman, general manager of the Apollo Backflow Prevention Division. When the flow is reversed, it can pull pollutants and contaminants with it into the potable water supply.
Protection of drinking water began in 1974 with the Safe Drinking Water Act. Even though attention to cross-connection points began in the 1970s, contamination is still a problem today.
A study conducted by the University of Southern California Foundation for Cross-Connection Control and Hydraulic Research (USCFCCCHR) 2002-2003, discovered that 9.6% of the homes included in the study group had direct health hazard cross-connections.
USCFCCCHR found that some homeowners are at risk for having their water sources contaminated. One homeowner was surprised when he found parasites in his drinking water due to contamination through his underground sprinkler system. His irrigation system failed at the same time a public water main broke. The nematodes were then sucked back into the water system. Later that evening, the homeowner found worms swimming in a bathtub he had just filled for his child to take a bath. The parasitical creatures, rust and debris were floating in the water because a cross-connection control device failed.
It is because of situations like the one described above that backflow devices are being required for homes as well as commercial properties. Using a cross-connection control program will help you avoid this situation, described in 50 Cross-Connection Questions, Answers and Illustrations by Watts. “An irrigation system is classified as a high hazard system by the Irrigation Association because of the possibility for contamination of the potable drinking supply,” said Chapman.
Why be concerned with cross-connection control devices?
First, and most importantly, irrigation contractors must understand cross-connection control because the installation of a backflow prevention device is required by law. Local municipalities decide what type of backflow device can be installed and who can install it. Some areas require a licensed plumber to do the installation.
With that being said, the local municipality code supercedes all others. Do the research before installing an irrigation system, because codes often vary from one township to the next. “They (the contractors) need to know that the reason they’re installing an approved backflow device is to protect them from liability in the event that water from the irrigation system were to pass into the drinking water system,” said Rick Fields, national territory manager with Wilkins (A Zurn Company).
In some instances, local municipalities do not have specifications in place. If this is the case, Fields recommends, “Do the install 100% in accordance with the manufacturer’s recommendations. Manufacturers are required to include a complete Operations and Maintenance Manual with each backflow. Reading the information can save the contractor the expense of having to re-do the installation.” He also suggested leaving the manuals with the building owner—their customer—for future reference.
Familiarizing yourself with local codes can also be a time saver for your company. Documentation, including permits, may be required by the local municipality. “All of the devices I install have to be approved and stamped,” said Dave Mantelli, Baker Mechanical in Rochester, New York. “We use the Department of Health (DOH) 1013 form, which consists of two parts, A & B.”
What is a cross-connection control program?
A cross connection control program is a working partnership between irrigation contractors, plumbers, health officials, property owners and certified testers. Cross-connection control programs are designed to prevent a reversal in flow of water, which could mix contaminants with potable water sources. Backflow prevention devices are often part of a cross-connection control program.
What types of backflow devices are available?
Air Gap—An air gap, which is a non-mechanical device, is effective against both backsiphonage and backpressure backflow. Because an air gap is a physical break in the pipe system and interrupts the pipe flow, it causes pressure loss. Usually, an air gap is used at the end of a service line because of the amount of pressure loss.
“An air gap is the best backflow preventer, if installed correctly. The physical break in the pipe ensures that water cannot flow back into the system,” explained Chapman. “The air gap must be two times the diameter of the pipe or faucet outlet.” For example, if there is a 1" pipe outlet, the air gap must have 2" of space between the bottom of the outlet and the flood level.
Atmospheric Vacuum Breaker
— The AVB is one of the simplest and most cost-effective devices available. The mechanical device prevents against backsiphonage, but not against backpressure. A float inside the device is lifted by water pressure. When the float is lifted, an internal disc seals. When the water supply is shut off, the disc drops down and opens downstream piping to atmospheric pressure. It must be installed 6" higher than all downstream piping and cannot have any shutoff valves downstream from the installation point,” Chapman noted.
Pressure Vacuum Breaker
— The PVB, unlike the AVB, can be used on a system that is under continuous pressure. It is effective against backsiphonage situations, but not backpressure. A springloaded float device and two test cocks make the unit a bit more sophisticated than its cousin, the AVB.
The PVB must be installed 12" above the highest point that occurs downstream, explained Kris Munson, national marketing manager for backflows for Watts/Ames/Febco. “If a head is 3' off the ground, the backflow must be installed 1' higher than the head,” he said.
—The dual check is manufactured with two independent 1psi loaded check valves. It can be used to prevent against backsiphonage and backpressure. However, it should only be used when protecting against non-hazardous contaminants. The unit does not have a shutoff or test port installed at time of manufacture and cannot typically be repaired or tested while inline. Given its comparatively small design (compared t o t h e double check) its capacity is typically less. “Dual checks are designed to meet a rated flow,” Chapman explained. “Because of its size, its rated flow (similar to maximum flow capacity) is 15gpm.” Unlike the double check below, the unit is held to only one standard of manufacturing: the American Society of Sanitary Engineering (ASSE), Chapman added. Depending upon local municipalities, dual checks are allowed in some areas.
—Double check devices are manufactured with two individual spring-loaded check valves with a minimum of 1psi that presses the check valve closed. Effective against backflow and backsiphonage, it's recommended for low hazard situations. Two ball valves protect against debris. Four ports are installed during manufacturing to allow for maintenance and testing. The double check is much larger in size than the dual check and has a rated flow of 30 gpm. It can be tested and repaired inline. Installation is commonly done in a meter box underground or in the homeowner’s basement. The double check must meet ASSE and USC-FCCCHR standards and also requires routine testing, once at the time of installation and once every year after installation.
Reduced Pressure Zone Assembly
—Referred to as an RPZ, this unit offers the most sophisticated level of contamination protection from backsiphonage and backflow. Even though an RPZ unit looks similar to a double check device, a few defining features distinguish the two.
The RPZ has two independent check valves. However, the first has a minimum spring-loaded pressure of 5psi and the second has a minimum of 1psi. Furthermore, the RPZ has an atmospheric relief vent mounted below the two double checks. Because it is relatively large, like the double check, it will cause flow loss and a pressure drop, explained Mantelli.
The double check is like a sealed piece of pipe and there is no way to tell if a problem exists unless it is disassembled or tested. However, an RPZ has a pressure-sensitive relief valve; it will leak water to let you know there is a problem. “The discharge does not mean the device is defective, it is designed to give an indication that cleaning or maintenance is needed,” Chapman added.
RPZs must be installed at least 12" above grade. Local municipalities always have the last say on what type of backflow device can be installed. However, in many instances the water purveyors will allow a more sophisticated device than what is required by code. “On Long Island, the water purveyor will often allow a RPZ even though a double check is code because an RPZ offers even greater protection,” Chapman said.
The RPZ is the only backflow prevention device recognized by the Irrigation Association to provide enough protection against health hazard contamination through the underground sprinkler system.
Continuing education is key. “I attend continuing education classes sponsored by the New York State Department of Health once a year,” Mantelli noted. “The guest speakers include engineers, manufacturers and state officials who keep us up to date on the latest requirements and new topics.”
Fields also suggested that contractors “develop a relationship with the local authority having jurisdiction, get their tester’s certification (requires 40 hours and a test) and join the American Backflow Prevention Association (ABPA)—www.abpa.org—and a local chapter, and attend a meeting every once in a while.”
In addition to complying with the law, the second most important reason to use backflow devices is because it can affect your own well-being. Irrigation contractors commonly work within their own neighborhood. “What happens if the potable water source in your neighborhood becomes contaminated because you didn’t install the correct backflow device or no backflow at all?” Munson said. “How would you feel if it was your kids, your family and your friends who were at risk?”