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Flow rate and system design

Discussion in 'Irrigation' started by F6Hawk, Jun 4, 2005.

  1. F6Hawk

    F6Hawk LawnSite Member
    Posts: 195

    I just measured my new meter with a few pieces stuck on it to get the pipe above ground. Time was 1800. Static pressure on our lines is 65 psi.

    3 runs, 5 gals each, no other water running. First run was 11 seconds, second was 10.5 seconds, and third was 10.5 seconds. 15.1 gals according to the meter, 15 in the buckets. That's 32 seconds for 15 gals, 60/32=1.875. 15*1.875= 28.125 gpm. Not bad off of a 3/4" service. (I am including all of this to have you smart guys check my math)

    So, now that I have my free-flow rating, what gpm per zone do you recommend I design the system around?

  2. kerdog

    kerdog LawnSite Member
    Posts: 129

    Hey F6Hawk-----

    So.....what size meter did you go for? And how is connected? To the existing 3/4 line? And what type 3/4 is it?

  3. F6Hawk

    F6Hawk LawnSite Member
    Posts: 195

    They installed a 1" Sensus SR-II meter onto the existing 3/4" copper service. The Tee is before the house meter, with the house meter getting the straight shot from the street, the sprinkler meter is 90° off of it.

    When I did my flow test, I used 1X1 TS, 3" of CL200, 90° up, 2.5' CL200, 90° left, 2' CL200, then another 90° down into the bucket. So the flow I got is with 3 90s, and not much pipe. I know this is an unrealistic flow rate, that is why I am seeking advice on how much I can actually expect to use after I run my main 100' to the valves, with all the fittings, etc.

    Is 20 gpm realistic for my system design, or should I plan for a higher/lower flow rate?
  4. kerdog

    kerdog LawnSite Member
    Posts: 129

    Hey F6Hawk----

    I would suggest keeping your zones between 10-12 gpm. If you shoot for 10 or 11, then you will have some room for adjustments, if needed. The 3/4 copper can give you about 12gpm at just under 9 feet per second, which everything I've seen or read, is acceptable. Stick with your 1" size for your main.
    It's good you can get class 200 pipe at a home improvement, here where I am, they carry sch.40 only. The class is available, at the irrigation supply, but not at the home improvements.
    Anyway.....sounds like it's time to break out the shovels!

    See ya---kerdog
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,650

    Your flow test means absolutely nothing unless you have a pressure gauge on the downstream side of the meter. Repeat the test with a downstream pressure of 50 psi. That will give you a more accurate picture. As mentioned before, the water velocity in that 3/4" copper is the important thing. Keep it within reason.

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