Agricultural Uses Of Backflow Prevention
With more and more chemical in use, in modern society, water experts are more and more concerned about the potential hazards of contamination of the potable, (drinkable), water system. As a result of this concern, there are a growing number of state and federal requirements for employment of devices which prevent the backflow of contaminated water into the potable water system. The plumbing industry is especially concerned about the locations where water from the potable water system, i.e. drinking water, emerges from the system. This can occur at your faucet, show nozzle, or outdoor spigot, to name three likely places. Should the emerging water contact external contaminants, there is a danger that when the flow ceases, the contaminated water will be drawn back into the potable water causing contamination of the drinking water. This very event actually occurs about 10,000 times a years, and has caused fatalities.
One of the greatest dangers of contamination from backflow occurs during the irrigation of crops. Modern agricultural engineers have designed a number of systems which allow farmers to inject insecticides and fertilizers directly into water being used for fertilization. The injection takes place close to the exit area of the tube. When the irrigation stops, the water that has already received the injection can potentially be siphoned back upstream and into the potable water supply. The poisons might then come out a drinking tap and potentially harm or kill a victim who drinks from that tap. Since this poses a serious threat to the public, government regulations require the use of backflow prevention during chemical irrigation. This type of back flow prevention is called “chemigation,” when it is employed to prevent the reflux of chemicals, and “fertigation,” when it is employed to prevent the reflux of fertilizers injected into the irrigation water as it flows towards the exit hole.
Because of the inherent dangers of chemigation backflow, chemigation valves generally employ a variety of prevention devices to insure that no contaminant reenters the potable water system. The first valve employed is called a “spring loaded check valve.” A check valve is simply a one way flap, or stopper, which prevent the reflux of liquid flowing in a tube. When the water flows in the right direction, it pushes the stopper out of the way, when the water is still, the pressure of the liquid trying to reflux pushes the flap or stopper shut. In a spring loaded check valve, a spring pushes the flap or stopper back against the valve opening, (valve seat), before the water has a chance to do it.
Use of a spring loaded valve in this type of back flow prevention is logical. Liquid flows in random directions. With regular stop valve, when the flow stops and the water begins to back up, some of the water flows against the valve lip or stopper and pushes it shut, but some of the water flows around the flap, and refluxes. Check valves work because the amount of water that refluxes before the valve shuts is small. But when the downstream water is contaminated with dangerous insecticides that are poisonous even in small amounts, then even a little water refluxing could be deadly. Therefore, scientists rely on the spring loaded check valve, which closes the opening much quicker.
But even the spring loaded check valve is not quick enough to prevent all the contaminated liquid from refluxing. So chemigation valves also include a downstream low vacuum drain, which drains contaminated water, and protects the check valve from continual downstream reverse pressure. The chemigation backflow prevention device also includes an air and vacuum relief valve, which prevents siphoning by allowing air to enter the irrigation tube, whenever flow strops and pressure drops in the tube. Finally, the whole system includes an irrigation port, downstream from the check valve, for adding the chemicals and fertilizer. The specificity of the agricultural backflow prevention system, and the intricacy of the regulations which protect the public, should deter anyone from taking our supply of safe fruits and vegetables for granite.
This article was brought to you by A-1 Plumbing of Baltimore, a Baltimore plumbing company. If you have concerns about whether the plumbing fixtures in your home are back flow compliant, A-1 encourages you to contact your area plumber. If you happen to live in the Metro Baltimore, Md. area, we will be happy to assist you. Our plumbers are certified in backflow prevention and will be happy to inspect your home.
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