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need help on a safe gpm

Discussion in 'Irrigation' started by woodlawnservice, Jun 23, 2013.

  1. woodlawnservice

    woodlawnservice LawnSite Senior Member
    Posts: 712

    City tap into main is 3/4" poly ran to the meter... which is 3/4x5/8. Guy at water dept called manufacture and says its a true 3/4 x 3/4, but there machines tbsts cast them are old so they still stamp em 3/4 x 5/8"... anyhow... pressure is supposed to be 65psi before meter... would I be safe using. 15gpm design you think? Customer wants a bid but I doubt he will let me.make a Tap to test until after the bid...thinking of using rain bird 5000s spaced about 30' apart....thinking I up size main to 1 1/4" to reduce my loss.and velocity over my 400' mainline run.... then go to 1" laterals .prob get about 5 rotors per zone
     
  2. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    Personally, I'd feel more comfortable at 10-12 gpm. Gives you room if the pressure or volume decreases over time, or if you need to add a head later on. We typically have 3/4 copper to the 3/4 or 5/8 meter, and bump to 1" at the valve manifold. I would go for 12 gpm max. I have some at 15-18 and they just struggle.
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  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,442

    no worries about the meter - the true meaning of 3/4 x 5/8 is that the performance of the 3/4 is fit into the smaller 5/8 package - the length of the 3/4 poly between the main and the system tells you where you top out for flow.
     
    Last edited: Jun 23, 2013
  4. 1idejim

    1idejim LawnSite Fanatic
    Posts: 8,824

    IMHO 1.25" belongs in the residential well drilling biz.

    1.5" minimum is my choice for mains. 2 - 2.5 for longer runs.

    Pressure loss @ 12 gpm is 1/2 of 1.25 pipe and about a 6th of 1 in.

    I know that i do mainly Ag related work where you are competing with the landscape irrigation crowd though.
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  5. Cape Atlantic Landscaping

    Cape Atlantic Landscaping LawnSite Member
    Posts: 37

    like Dana posted 10-12 GPM in my experience you need to stay conservative and think about worst cast scenarios down the road.
    Is this a new development and other Holmes are to be added later ?
    In my town the city has a greater demand in the summer due to all the tourists.
    Also I would use 1 1/2 SCH. 40 main and 1 inch SDR 21 pipe for the lateral lines not poly
    this should get you to the 30 ft. you need
     
  6. woodlawnservice

    woodlawnservice LawnSite Senior Member
    Posts: 712

    Thanks guys... I'll design for the lower flow... my length from the tap on the main to the meter is 30' and is poly. After the meter I can step up to 1.5 sch 40 and on laterals go 1" sdr 21. I'm not a personal fan of sdr 21 but.... it does flow more, cheaper, and when installed right I shouldnt have a problem. The cost of having a irrigation meter set for 1" is only $550.... that being said I really though about having the homeowner do this.... that additional cost into breaking the system.into more zones, heads and such will prob make that a viable option? Thoughts on that... so its b 1" poly from tap to meter with 1" meter... rhen could I get away with 1 1/4 or would u guys still stay with 1.5" schedule 40 for the 400' of mainline... this job how I have it designed at now already has 8 zones on it... I hate to bring gpm down more and then more zones... I dont really care to have him watering all night long..lol
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  7. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,442

    If the main (and the tap) were accessable, you could just upsize the 3/4 pipe, but the specialty upsizing adapters might not be easy to find.
     
  8. woodlawnservice

    woodlawnservice LawnSite Senior Member
    Posts: 712

    I'll check.into.those. never used em.. would u consider a whole new 1" tap to get my gpm up to the 15 ish number?
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  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,442

    It depends on how much acreage you're watering. A one-inch tap would get you closer to 20 gpm. And a new tap could also be fitted so as to allow a larger supply line, eliminating a performance bottle neck.
     
  10. woodlawnservice

    woodlawnservice LawnSite Senior Member
    Posts: 712

    3/4 acre lot and your suggesting a larger supply like say.. 1.5" to the meter?
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