SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I am in the process of designing my inground sprinkler system. My static pressure on my water line is 60PSI. The size of my main water line is 3/4 inch. I've installed a 3/4 inch reduced pressure back flow preventer right after my main line water filter (which is right after my water meter). I know that I have to go out to 1 inch to the valves (the valves are also 1 inch) and my question is this: Can I go 3/4 inch out the house and into the ground then tie the 3/4 inch copper to a 1 inch SCH 40 PVC pipe which will then tie into the manifolds for the valves or should I increase the size of the pipe to 1 inch right after the Backflow preventer and go out the house into the ground with 1 inch? i would prefer going out the house with 3/4 inch into the ground and increasing to 1 inch where the copper will meet the PVC only because i have left over 3/4 pipe and fittings left over from another project.


I am going to have a 7 zone system with 1 inch poly going from the valves to 3/4 inch poly that will feed the sprinkler heads. Some of the heads have a 3/4 inch inlet and others have a 1/2 inch inlet. Some of the 3/4 inch pre-assembled swing joints that I have seen are really 1/2 inch pipes with 3/4 inch swing joint threads. Can these be used or should I try finding / building swing joints with 3/4 pipe and 3/4 inch threaded swing joints?


Thanks!

I should also note that the zone valves will be less then 10 feet from the Reduced pressure Back flow (which is tied into the main line). So I will be running about 5 feet or so of 3/4 inch pipe to 1 inch SCH40 or just go all 1 inch from the 3/4 inch Reduced pressure back flow.

Thanks Hook,

What I've decided to do was to increase the diameter of the 3/4" pipe right after my Back Flow preventer to 1" while it's still in the house and go 1" all the way out and into the ground to the 1" SCH40 pipe that will be tied to a manifold for the 1" sprinkler valves I have. This way I can save on losing some PSI while going out to the valves.

Thanks again.

Quoted from "HooKooDooKu"

You can bounch back and forth between pipe sizes all you want. You just have to realize that smaller pipe sizes increase pressure losses as the water flows through the smaller pipe as a higher speed. The other thing to consider is that you don't want to have water travelling through pipes at a higher speed of 5 feet per second. For 3/4" pipe, that limits you to 6gpm to 8gpm depending upon what type of pipe.
You can find pressure loss and water speed charts here: http://www.hunterindustries.com/resources/pdfs/technical/domestic/lit091w.pdf