Nothing is more serious in irrigation than backflow. If an irrigation contractor allows an organic contaminant or pesticide to enter the public water supply through an irrigation system and public health is compromised, we are all in serious trouble. The issue won’t be whether we use water responsibly, it will be whether the health of plants outweighs the health of the public. You know who will win that fight.
Some health departments don’t know who to trust with the protection of public water – plumbers, irrigation contractors, landscape contractors, fire sprinkler installers, sales clerks at hardware stores or property owners. The backflow device is where some states draw the line. Many states require backflow protection and annual inspections of those devices by certified inspectors.
Fortunately, the irrigation industry has technology to prevent back siphonage of contaminants into a public water supply, whether that is a municipal water supply line or a well. There are four basic types. They range in price and reliability. Always check the local requirement for backflow protection and never cut corners with this aspect of irrigation installation.
The current philosophy about backflow regulation is more device-based than application-based. To guard against contamination, local water agencies usually adopt one of two code requirements for irrigation systems: the Uniform Plumbing Code or the International Plumbing Code. In the eyes of these codes, all water users are considered as one.
Responsible irrigation designers, distributors and contractors are aware of state and local backflow requirements and comply with them.
Explaining backflow requirements and costs to customers requires a basic knowledge of backflow prevention devices and a specific knowledge of local regulations. In some cases, the additional cost of meeting backflow requirements discourages customers from purchasing the irrigation system they really need or encourages them to have their systems installed without meeting codes.
In locations where codes exist but enforcement doesn’t, irrigation contractors could see systems that do not meet codes. When they have to compete against installers who do not meet codes, the situation becomes a matter of ethics and ultimately one of protecting natural resources. To install an irrigation system without meeting recognized standards just to get the business – whether the locality has codes or not – is wrong.
The best way to resolve this problem is to employ individuals knowledgeable about BPD operation and testing. Granted, these devices appear complicated, but information is available that shows how they operate and includes step-by-step procedures for testing them.
BIG PICTURE LOOK. In addition, how irrigation system components impact BPD performance is especially critical. “Water hammer caused by improper system design or small things, like solenoid malfunctions, can make a backflow device perform improperly,” explained Tony Arthur, marketing manager, Watts Regulator, North Andover, Mass. “Checking water filtration upstream of the device can ensure many years of trouble-free service.”
Wye strainers, included with some back-flow prevention setups, clog easily when debris enters the system during repairs or new construction of the water supply system. Water sources, such as wells and lakes, present a greater chance for debris, which can cause seals to seat incompletely. Regular cleaning of upstream filters is clearly more important with well and lake sources.
A good time to check the operation of the BPD is during system troubleshooting. Unfortunately, in some areas, the irrigation technician is not supposed to touch the BPD. He or she is required to call in a plumber or other certified inspector. Or, if a technician does work on a device, an inspector has to check it before the system can be placed back in operation. By having a certified inspector on staff and stocking service trucks with common seals, springs and testing devices, contractors can greatly improve the maintenance process.
CONTAMINANT OR POLLUTANT? Backflow codes recognize two types of water problems. If a material entering a public water source by backsiphonage constitutes a health hazard, it is termed a contaminant. If the material is not a health hazard, but results in changes in the water that are objectionable to users, such as taste, odor or appearance, it is considered a pollutant.
The American Water Works Association recommends irrigation systems used to apply pesticide products include a reduced pressure principle backflow prevention assembly. This protection comes at a cost, both in the price of the backflow prevention device and the pressure lost. Systems that apply only water to the landscape, according to the AWWA, should contain any of the following: a double check valve assembly, a pressure vacuum breaker or an atmospheric vacuum breaker.
Therefore, if you add a fertilizer or pesticide injection system to an irrigation system, there is a good chance the BPD will need to be changed.
MORE PROTECTION, LESS PRESSURE. The simplest type of BPD is the atmospheric vacuum breaker. Water flowing in the proper direction pushes the valve up to close an air gap opening. When the water stops flowing or moves in the wrong direction, gravity closes the valve, opening the air gap to relieve backpressure. Not only is this the simplest and least expensive type of BPD, it provides the least friction and pressure loss.
A pressure vacuum breaker is slightly more advanced. A spring, not gravity, closes the valve when flow ceases or backflow occurs. The air gap is also spring loaded and remains closed except during backflow situations. Safety does come at a price, however. More precautions create more friction and greater pressure loss.
Another option, the double check valve, is essentially two pressure vacuum breakers is a row, but contractors need to be aware that greater protection necessitates more pressure to operate the irrigation system.
The ultimate in backflow protection is the reduced pressure principle assembly. It includes two spring-loaded valves with a spring-loaded relief valve between them.
The worst case scenario for pressure loss is 20 psi. So, if a system requires pressure at the sprinkler head of 45 psi and the local supply is 50 psi, the sprinklers might not deliver the necessary coverage.
If sprinkler heads without check valves are located in low areas of turf treated regularly with pesticides, contractors should design the system for a higher level of protection and, therefore, a greater loss in pressure. Better backflow protection with fewer heads per zone and more zones per controller can solve the problem. When uncertain, contractors should plan for more than atmospheric pressure breakers and include a controller capable of handling extra zones.
Contractors performing a significant amount of irrigation installation should consider training or hiring someone to act as a backflow specialist. (Contact the Foundation for Cross-Connection Control and Hydraulic Research at 213/740-2032 for information). Also, be aware that backflow devices require extra freeze protection and winterizing, and any BPD in a public location should be protected with an enclosure.
The more seriously contractors take backflow protection, the less likely they are to be restricted by regulations in the future. An enormous amount of security is worth a relatively small amount of training.
The author is owner of IrriCOM, which serves as the communications arm of the Irrigation Association.
Explore the June 1998 Issue
Check out more from this issue and find your next story to read.
