Pipe Size

Discussion in 'Irrigation / Sprinkler Forum' started by Pochi, Jul 1, 2009.

  1. Pochi

    Pochi New Member

    Messages:
    3
    I am excited installing a sprinkler system for the first time. This will be a big challenge for me.

    I have just started collecting data and already have a question, what size pipe I should use. Here is the data:

    Water Meter Size: 5/8"
    Service Line: 1" PVC
    Water Pressure: 55 PSI
    Water Flow: 8.6 GPM

    Is this enough to figure out what size pipe I should use? I am not sure if I should use 3/4" or 1". I would appreciate anyone who has had experience.

    Thanks,

    Pochi
  2. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    If you have your yard divided up into zones the overall pipe size won't be so critical. I've got 1" serving 6 zones, 5-8 heads per zone. Every zone is a 1" trunk with 1/2" flex to each head.

    I also might have really good pressure, my city has a dedicated "grey" water system for sprinkers...
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    size

    You are going at it backwards. First you figure out your volume and pressure, then you decide how many heads that will handle on each zone, THEN you calculate the pipe size needed. If you put too many heads on a zone, it will not matter how large the pipe is, they will not water properly.
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Based on your info, as a general comment I would say run 1" pipe from the source to the location or locations of your valve manifolds. Then the distribution can be 3/4, with some 1/2 inch used for branches to just one or two heads.

    Based on the 8 GPM number, it will be important to divide your yard up into as many zones as required so that each zone does not exceed that number.

    I don't know where you took that GPM measurement. (Possibly off a 1/2" hose bibb in the back???). Even a 5/8 meter should deliver more than 8 gpm through 1" pipe. Nonetheless, you will be well served to use more zones rather than less.
  5. BRD

    BRD New Member

    Messages:
    53
    Location:
    northeast
    I agree with Jimbo. Run 1" pipe throughout. Why sacrifice any pressure loss through the pipe, and the cost difference is minimal between 3/4 and 1".. You have 55 psi static pressure but once it starts moving you will have friction loss through your service line, water meter, backflow device, zone valves and piping. Also there may be elevation differences to take into account. 8 gpm through 1" pvc or polyethelene will have minimal pressure loss. ( 1" class 200 pvc looses approx. 1psi /100 ft at 8gpm vs 3/4 class 200 looses approx. 3.2psi/ 100 feet. You can pipe size from head to head but to make it simple go 1" all the way
  6. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,358
    Location:
    Yakima WA
    Irrigation system design is a bit more complex than connecting pipes and adding sprinklers. For one thing, your water supply is a very limiting factor. The meter is very small and with the fairly low pressure, you will have some real problems running many heads on one zone. You need proper backflow prevention to avoid cross contamination of the water supply, so everything must meet City and EPA codes. In my area, this is enforced big time with required annual inspections of every home system at the homeowners expense. Here's what I suggest. See if there is a irrigation supply house in your town. Go see them see if their designer will design your system for you. You'll need a scale drawing plus all the data on water supply, pressure, meter, etc. It's been 25 years since my system was designed that way, and your supply house may not do what mine did, but the design was FREE with the stipulation that I buy all of my supplies from them. Heck, their price was less for professional grade stuff than the Big Box store wanted for there second rate stuff. Even if you have to pay for the design, you will be money ahead because the system will work with out dry spots or other problems. FWIW, I replaced a 5/8" meter with a 1" meter, put in a tee with on leg to the house and the other to the backflow preventer then to the manifold. It may have been a bit overkill, but the difference in cost between a 3/4" meter and a 1" was not that much and the labor to install was the same of either.
  7. Pochi

    Pochi New Member

    Messages:
    3
    Thank you for all the advice.

    I didn't know you can mix 1" on the main line and use 3/4" on the zones. This makes sense so that's what I will go with.
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