# Does a 3/4" backflow mean I should use 3/4" main lines?



## Glen_Cove_5511 (Jun 13, 2020)

Starting my initial plans to install my own irrigation system next month and I wanted to ask the question regarding the size of my main lines compared to the backflow preventer that I have already purchased. Thanks!


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## Glen_Cove_5511 (Jun 13, 2020)

When I do my bucket test at a hose bib, I am getting 7 GPM if that helps with my decision.


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## corneliani (Apr 2, 2019)

Not necessarily, 3/4" water meters & back flow preventers are standard residential fittings. Any pressure loss that occurs through that bottleneck is negligible at that point in the system and usually unaccounted for, unless you're limited to start. Which brings up the 7 GPM you measured. If you're taking this reading downhill from the PRV you're probably getting a lower reading than actual. Ideally you measure this at the point where you'll tap off for your valves but that requires digging & setting up a temp spigot. In my opinion, if you don't have long runs and have a somewhat-compact lawn where you can be efficient with your layout there's no reason you can't continue with 3/4" CL200 pipe for your main trunk & branch lines. The PSI loss over 100' of 1" vs 3/4" pipe, for ex, is not even 2psi. But if you're pushing the limits with low PSI & GPM then bump up to 1" trunk line. I can't imagine you'll have a lot of that for 4000 sqft yard


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## Glen_Cove_5511 (Jun 13, 2020)

Thanks @corneliani... I appreciate the reply. The backflow preventer has not been installed. I did the GPM test from the same line a hose bib is located and where the irrigation feed will come from. I was thinking 4 MP Rotators on each zone. Not sure which nozzles yet since the majority of the 4,000 sq. ft. is on a 10° slope.


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## corneliani (Apr 2, 2019)

So you're tapping off the water bibb, and then going underground? Are you adding a controller & valve, or will you operate this manually? Lastly, howw many zones, just the one?


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## Glen_Cove_5511 (Jun 13, 2020)

@corneliani... The plumber said he was going to T off the hose bib and provide that feed to the backflow outside. From there it will go to a manifold with 3 zones. Pressure at that hose bib is 80 psi. I will be using a Rachio 3 to control the valves.


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## corneliani (Apr 2, 2019)

Glen_Cove_5511 said:


> @corneliani... The plumber said he was going to T off the hose bib and provide that feed to the backflow outside. From there it will go to a manifold with 3 zones. Pressure at that hose bib is 80 psi. I will be using a Rachio 3 to control the valves.


Hose bibs are usually plumbed with 1/2" pipe. :shock: I hope that's not his plan.


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## Glen_Cove_5511 (Jun 13, 2020)

No, the supply to the bib is 3/4" PEX. He's putting a T on the PEX to supply the irrigation with 3/4".


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