Mazzei Injector Company, LLC

Backflow Prevention and Anti-Siphon Examples

About Mazzei® Injectors
Selecting an Injector
Injector Performance
Typical Installations
Chemigation Safety
Technical Bulletin VII: Supplemental Check Valves
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Fertilizer/Chemical Injection
AirJection Irrigation
Wastewater Aeration for Odor Control
Produce Wash-Water Aeration

Example 1

Example 1 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. The injector is installed above the liquid chemical or fertilizer tank.

A simple atmospheric vacuum breaker is placed on the injector bypass line, also above the level of the chemical tank. This assures a positive anti-siphon system during main flow shutdown. A Reduced Pressure Principle backflow prevention device is installed on the main flow line upstream from the injection equipment to prevent any possible backflow from that point.

 

Example 2

Example 2 depicts a Mazzei® Injector installed in conjunction with a centrifugal pump, which boosts 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 supply pump is running.

Since it may not always be practical to install the injector above the level of the chemical tank, this illustration 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 check 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 backflow prevention device should always be installed in the main flow line upstream from any injection equipment.


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