Starting design - check my flow/pressure please

Discussion in 'Irrigation / Sprinkler Forum' started by Lakee911, Oct 2, 2011.

  1. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Hey all,

    I'm going to be starting an irrigation system plan this winter and I just got done replacing some piping in the house to ensure that I have the maximum amount of water pressure and flow available in the house. Can I get a gut check that these numbers are okay?

    I open the outside spigot to 100% and let the water flow for some time. I watched the dial on my meter spin and recorded the diffrence in volume and the time it took. I came up with 12GPM @ 44PSI-dynamic (measured on a faucet in the basement while outside spigot on) and 76PSI-static (measured on outside faucet) with nothing running.

    Here's what is between the water main and the spigot:
    * 8" water main in the street
    * 10' of size unknown lead pipe between main and curbstop
    * curb stop, unknown size
    * 35' of 3/4" copper between curb stop and angle stop in basement installed circa 2010
    * angle stop, 3/4"
    * 8" of 3/4" copper between angle stop and 1/2" nipple
    * 3" of 1/2" nipple to meter
    * 5/8" meter, install date unknown
    * 3" of 1/2" nipple after meter
    * approx 10' of 3/4" copper and through 2 full port 3/4 sweat full port ball valves installed day or two ago :)))
    * 12" freeze proof spigot, appears to be 1/2" in size.

    What do we think? Okay? Seems about right?

    Thx,
    Jason
  2. mike1059

    mike1059 irrigation tech.

    Messages:
    56
    Location:
    Portland, OR
    your numbers look good so far. the next question is where you plan to connect your system to your water source. the best place would be within a couple of feet of the meter. then factor in friction loss and flow rates for your planned heads. I would plan on using a 1' backflow, 1" mainline pipe and 1" valves then 1" or 3/4" pipe for your station lines.
  3. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Good. :)

    I created an extra tap off of the new 3/4 line for the new system. I wasn't planning on 1" line for the mainline, but then really I hadn't given it much thought. I guess I had assumed that 3/4" wasn't going to be a problem. Is the difference in line loss going to be that much? If I look up the difference in losses, how do I translate that into ultimate difference of flow?

    For now, my system will only connect up to a couple of existing drip zones and one or two zones in the front yard for grass. This winter I'm going to probably send off for a plan by one of the major companies and see what they think and I'll tweak from there. Who is good and free? This will also be DIY so I can't have them recommend like 45 pop up heads...just a few rotors would be preferred!

    Thx,
    Jason
  4. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Also, what is the school of thought? All manifolds together in one place or main line through out the yard and tap off to valves as needed?

    Thx,
    Jason
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,347
    Location:
    Yakima WA
    Not part of your question, but you need to understand that your back flow device should be tested and re-certified annually. Some places, like where I live, mandate it to the extent that failure to have it tested will result in your water being shut off. The city provides the first test, then I receive a list of approved inspectors to choose from. I know some places don't bother to enforce the Federal laws regarding back flow prevention, but that doesn't make it right. It might be money well spent to have a professional sprinkler company at least design your system. The would require a scale drawing in addition to the data you have already listed. Years ago, I had this done and the design was free provided I purchase my pipe, fittings, and sprinklers from them. To top it off, the quality of their sprinklers was better than discount stores and cost less as well!
    Last edited: Oct 2, 2011
  6. mike1059

    mike1059 irrigation tech.

    Messages:
    56
    Location:
    Portland, OR
    although the friction loss will not be that much the smaller pipe will increase the velocity thus increasing friction loss. As far as valve placement that varies by designer. For the design most of the big names like rain bird or hunter have free design links on their site home pages.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    Everything relates to the SIZE of each zone and the volume demand for it. Your specifications will work if you have several moderate zones, but NOT if you try to use a couple of large ones.
  8. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    I am aware of this and I will have an approved device. My city does require annual testing--anything for them to get their buck, right? ;) I haven't selected one yet, but it's on the plan.

    That's a good idea ... I never thought of that. I'll start with the free design online and see what it looks like and I might proceed this way. Thanks.

    I see what you mean. Quick calcs show that in a 3/4" pipe, 12 GPM is 8.7 FPS @ 23.9 PSI/100FT loss and 1" pipe, 12 GPM is 4.9 FPS @ 5.5 PSI/100FT loss. I guess what I still don't understand is, let's suppose I did use 3/4", at 23.9 PSI less at the point of use, what would my flow be? Probably no longer 12. Right?

    Noted. Thanks. What's the rule of thumb for designing at a given flow/pressure? Obviously I'd want to build in some reserve or fudge factor...just how much?

    So doesn't matter?
    Last edited: Oct 3, 2011
  9. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Attached is my plan for the front yard. Couple zones perhaps? I sent it off to Rainbird and we'll see what they think.
    sprinkler front2.jpg

    Can someone please edit the title of the thread and remove the "-check my flow/pressure please." We're building on this now! :)

    Thx
  10. mike1059

    mike1059 irrigation tech.

    Messages:
    56
    Location:
    Portland, OR
    it will be my guess that they will recomend three maybe four zones for the grass and one for the beds. as for valve placement a single manifold will likely be the recomendation.
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