# Tapping main line.



## gm560 (Feb 22, 2018)

I did some digging around my basement and am considering tapping my main water line. Currently, my DIY system is running off a hose bib. At the spigot I am getting ~6 GPM @ 60 PSI. Its enough for a handful of heads per zone. I was thinking about tapping into the main, but had a few questions. First, the main line comes into my basement as 3/4 and immediately goes into my AmericanWater meter. It comes out the other side as 1/2 that supplies the rest of the house. If I tap the main while it is 1/2 copper, will I get any performance improvement over the spigot? I could certainly make it more direct to the system (it takes a half dozen turns prior to getting to the bib ), which I am guessing is decreasing my flow. If I tapped the 1/2 copper and used 3/4 pex to the irrigation, would that help? I realize I would need to incur some extra cost of installing a backflow device if I did this, so trying to do the cost benefit analysis.


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## g-man (Jun 15, 2017)

Is the output of the meter 1/2 or 3/4 and downsized to 1/2in?

Look at this page of irrigation tutorial. At the bottom it has a table with the safe GPM based on the pipe. https://www.irrigationtutorials.com/gpm-psi-municipal-water-source/ For 1/2 copper it is 6gpm. If you want more GPM, you need to up your pipe diameter.

You wont gain much unless you could tap into your 3/4in cooper. If the output of the meter is 3/4, then you T there and then reduce to 1/2in for the rest of the house. Otherwise you will need to have the meter changed or add a meter just for the irrigation.

Also, if you use PEX, go one size bigger. The ID of PEX is small, so a 3/4in PEX=1/2in copper. To help the backflow I even go two size bigger. Larger ID will not hurt a thing (other that a small price difference), but it helps in avoid pressure losses thru the backflow until the valves.


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## JDgreen18 (Jun 14, 2018)

Hey @g-man just curious how much flow or gpm do you gain from going to 3/4 from a 1/2 inch. My main line coming in was 1 inch so my contractor tapped in so my irrigation is running off 3/4. That's a 50% increase right


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## g-man (Jun 15, 2017)

The same link in irrigationtutorials has a table. For cooper, 1/2in is 6GPM; 3/4in is 11GPM and 1in is 18GPM. It follows an exponential curve based cross sectional area of the ID of the pipe. The area of a circle is pi*r^2.

This is one that bigger is better, but if your system is already designed and your zones are working, then you wont gain anything changing it now. More available GPM means that you could design for more heads per zone. I prefer to not save $ on zones and be able to section the zones based on sun exposure (avoid a zone that waters full sun and full shade).


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