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New Member


Monday, May 28th 2012, 12:23pm

Exsisting system redo HELP

Hello I have a few questions I hope someone can answer before I pull my hair out, I have some basic understanding and have read alot on design all which goes against what I currently have in my yard. I am redoing my system due to age and broken pipes fittings Ect. but I can not understand how or why it is ok the way it is, I currnetly have a 5/8 meter with 3/4" PVC main line I flow test about 12 GPM using bucket and stopwatch with about 45 psi static , my system is all 3/4" main lines with 1/2" laterals adding up all the spray tips on a 15 head zone I come up with 15.7 gpm and close to 17.5gmp on others. my question is how is this possible if I only have 12 gpm of supply ? And I am wanting to redo using all 1" mains and 3/4" laterals but will this help and can I too get that kind of flow due to what water is in the pipes ? Sorry for length I just want to do this right once but dont want to have more zones then I need and I know that the current setup is fair and has provided a good watering for years but i want to improve if possible. Thanks
Also would replacing my 3/4" Sch40 main from meter to 1" Sch40 help its about 60' total to the manifold conection point.

This post has been edited 1 times, last edit by "Backline" (May 28th 2012, 12:33pm)


Supreme Member

Posts: 5,331

Location: Metro NYC


Monday, May 28th 2012, 2:02pm

Read your water meter while timing it with your wristwatch, and get a true reading of the flow.


New Member


Monday, May 28th 2012, 2:06pm

While running a zone or open spiot ? I guess what I am asking is it possible to gain GPM buy using larger pipe to hold more volume as a supply before the heads ?

Central Irrigation

Supreme Member

Posts: 371

Location: Central Minnesota


Monday, May 28th 2012, 2:45pm

In a round about way, yes, you will gain more water at your sprinkler heads. Using larger diameter pipes decreases pressure loss. You can't gain more volume than what your house can supply, but you can increase dynamic pressure by using larger pipes.
Rule of Thumb: Do not exceed flow for the following PVC Pipe Diameters
1 1/4"....<35GPM
Note...Poly pipe has different limits.
Based on your 16GPM zone, you are losing roughly 6psi in that 60' stretch of mainline. Compare that to 2.5psi lost if it were 1" PVC. Keep in mind, your 1/2" laterals are where you're losing alot of pressure.
I don't understand why people switch lateral size. Keep it all one size. Saves time and limits the number of repair parts needed.

This post has been edited 2 times, last edit by "Central Irrigation" (May 28th 2012, 3:07pm)


New Member


Monday, May 28th 2012, 10:35pm

Thanks, thats the plan I got hundreds of feet of pipe being dropped tomorrow and will start then. Thanks for the help and replies.

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