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Friday, April 4, 2014

Backflow Prevention and Pressure Reduction

I have now spent some time looking at the situation I have and what I need to install: a backflow preventer and a pressure reducer.

The backflow preventer is required, because I am going to have my rainwater storage connected to the irrigation system, the irrigation system, in turn, is connected to my potable water system that is supplied by the municipal water district.  I do not want non potable water (rainwater, in this case) to infiltrate either my potable water supply (domestic water for the house), or the municipal water supply system.

If I do not install such a device, and if the pressure reduces on the municipal system, for some reason beyond my control, and the water pressure is higher on the rainwater storage system side, then water could flow in the wrong direction and contaminate the public water supply and my domestic water supply.

The pressure reducer is needed to reduce the water pressure in the irrigation system from the nominal 50 psi pressure of the water coming from the municipal system to 30 psi for the irrigation system.  There are a number of reasons to reduce the pressure.

The sprayers in my irrigation system were designed to optimally function at 30 psi.  The spray heads will last longer, will distribute water in a more even pattern over their range, and it will most importantly, reduce misting which could waste as much at 40% of the water being used by having it carried off into the air.

Needless to say, the reduction in pressure will most likely reduce my water consumption (and water bill) by at least 25%.  I may have to compensate for the lower pressure by leaving the spray head active during a given cycle by extending the time it is on.

There are many kinds of devices to accomplish these functions on the market, most are relatively expensive for their size, but cheap when it comes to their ROI.  I will try to include here what I am finding and why I am choosing the specific devices.

There seem to be very specific instructions on where and how to install these devices.  For example they must be located substantially above the ground (unless you go for a much more expensive device) and also be higher than the sprinkler heads.

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