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Recently, the EPA and other Federal and State regulatory bodies have voiced concerns regarding backflow prevention and anti-syphoning in conjunction with the injection of fertilizers or other chemicals into irrigation systems. Generally, these regulations are designed to safeguard individual household or community water supplies and underground aquifers from contamination. This is accomplished by eliminating the possibility of backflow into a well or syphoning into a water system once the irrigation water is shut off.
This first example depicts a Mazzei Injector installed around a point of restriction such as a regulator valve, which creates a differential pressure in the main flow line, thereby allowing the injector to produce a vacuum for chemical induction into the system.
Note: The injector is installed above the level of the fertilizer or chemical tank A simple atmospheric vacuum breaker is placed on the injection bypass line, also above the level of the chemical tank. This assures a positive anti-syphoning system during main flow shutdown. A reduced pressure principle blackflow prevention device is installed on the main flow line upstream from the injection equipment to prevent any possible backflow from that point.
This example depicts a Mazzei Injector in conjunction with a straight centrifugal pump, which boost a portion of the main flow through the injector, thereby creating a differential pressure, allowing the injector to produce a vacuum for chemical induction downstream from the pump. When employing this method, the auxiliary centrifugal pump must be interlocked electrically with the main supply pump so it can be operational only while the main pump is running. Since it may not always be practical to install the injector above the level of the chemical tank, this illusion shows methods of isolating the injection system from the main flow line (during shutdown) when the injector is installed below the tank level. Note: A one-way valve is installed on the injector bypass line prior to the inlet of the injector. A normally closed hydraulic shut-off valve is installed on the injector bypass downstream from the outlet of the injector (this valve will automatically close during shutdown of the main flow line). A normally closed solenoid valve (electrically interlocked with the pump) can also be used at this point. As in example #1, a reduced pressure principle blackflow prevention device should always be installed in the main flow line upstream from any injection equipment.
Inset: Another method of isolating the chemical from the main flow line during shut-down is the use of a small normally closed solenoid valve on the chemical suction line between the injector and the chemical tank. This valve must also be electrically interlocked with the pumping plant. A positive shut off of the chemical line will then occur during a power or breaker failure or at any time the pump is stopped.
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