I also have a 1" copper supply line with a 5/8" meter. My water company charges more for a 3/4" meter even though you use the same amount of water. Anyway, my supply line is about 45ft long from the street and I tapped into the meter about 2ft after it. I'm using 1" Sched 40 for my application. I have about 30ft of 1" Sched 40 PVC before it exits the house and hits a 1" Wilkins PVB. If I open the shut off valve I get a huge amount of flow compared to the measley 7.5GPM from my hose bib. My static PSI is 51. The problem is that the meter is rated for a maximum flow rate. For instance my Badger brass meter is only rated for 20GPM max if it is a continuous flow of water. Even though the manufacturer says 20GPM that still feels awful high to me.
With that high flow rate you may get a huge amount of flow when it is free flowing but you may only be getting a few psi of pressure once it exits the 1.25" PVC. Designing for 25GPM means you won't have any pressure to lift the spray heads or throw the water more than a few feet if you max out your flow. Hopefully, I worded that elegantly enough to be understood. You have a lot of pressure loss calculations you'll need to do. I designed my entire system based off the information at
www.irrigationtutorials.com. If you haven't already I suggest reading the entire site multiple times until you understand what he is saying and then start designing your plumbing and zones. Since you already have 1.25" PVC in place you won't need to redo that part of it. It should be more than enough.
And and even more important is that if you start flowing a high GPM once that zone valve snaps closed you could be looking at a huge pressure surge in the irrigation system as well as throughout the house. This is commonly called water hammer. Ice maker and toilet bowl lines are usually the first thing to blow out. At 25GPM the water will be moving at about 6.5 ft/sec through the 1.25" PVC pipe. And even faster through the 1" copper house supply and meter. The rule of thumb is not to exceed 5 ft/sec of water velocity.
For what it's worth, my largest zone is only using around 9GPM. But I am being very cautious with my design.
This post has been edited 1 times, last edit by "ReddHead" (Oct 5th 2010, 9:29pm)