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System design question.

Discussion in 'Irrigation' started by GrazerZ, Nov 25, 2007.

  1. GrazerZ

    GrazerZ LawnSite Senior Member
    Posts: 670

    Here is the situation. I have a job that we were told that the service line was 1 1/4" but turns out to be 1" poly which changes everything. Heres why:
    service line 1" poly 550' long from street.
    5/8 meter
    Delivery line 3/4"
    3/4" dual check
    static pressure is 45psi with regulator. belived to be 55 wide open.

    Heres my question. I would like to run safely from 5-10 gpm.
    I know that I can do about 4-5 but it would be marginal. The calculations I did tell me that at 12 gpm I would get a wooping 21 psi. How would you go on this one? its a 45 head system at aprox 30' spacing. I'm considering adding a pump to the system to insure its right but would like to avoid. I'm worried that either way I will be restricted because of the 550' poly service line. Any advice is welcome. This is a bit diferrent than what I've incountered so far. Thank you in advance.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,694

    Bypass the regulator. Cut the system into bite-size pieces. Use R-50's. (oops!)

    Better yet, make a connection very near the street, somewhere in that supply line, and use a second meter for the system.
  3. GrazerZ

    GrazerZ LawnSite Senior Member
    Posts: 670

    I'm going to have the connection to the line made before the regulator. Another connection in the service line is not an option. My issue is with the dynamic pressure.
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,694

    With a 550' service line, the question arises about how large a property is this, and whether there is enough flow to cover the property.
  5. GrazerZ

    GrazerZ LawnSite Senior Member
    Posts: 670

    I think thats valid. I do belive I will be ok. The property in relatively shaded with good water retaining soil. We also need less water here in Maine as a rule as well. 1" a week is good for most turf. I plained on reducing the gpm usage for each zone so that the 1" will be ok. heres what I came up with from a design calculator:

    Pressure at point of connection: 55 psi
    Dynamic pressure at point of connection: 26.2 psi
    Design capacity at point of connection: 12.3gpm
    Estimated pressure available for sprinkler opperation: 21psi

    what do you think? What would you do?
    Would you use only lets say 5gpm to conserve pressure? Or would you go straight to a booster pump as I'm inclined to do? I've been looking at these pressure mate set ups, just for the irrigation system.
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,694

    A booster pump will have a good chance of creating negative pressure in the supply line, or the house, if you aren't boosting the entire home's pressure. That would take you part of the way to a 'backflow event' ~ A poly line is not designed for vacuum service. Don't use any 'set-up' if you go booster. A one-third horsepower jet pump is probably the safest fit for a dinky water supply. Even if you have to pay more for the 1/3 HP, in comparison to a 1/2 HP, while getting less of a boost, you don't want a pump that can pull more than the water supply can push.
  7. GrazerZ

    GrazerZ LawnSite Senior Member
    Posts: 670

    Thanks wet boots for the replys. Would love to hear from someone else as well though. I have a appointment with a plumber on wensday to crank out the pressure regulator and then spec out for the backflow and stub out. Guess we will see what happens.
  8. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    If no one else has replied, then you can probably assume all contributors agree with boots.
  9. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,976

    Throw a couple of extra zones in...screw the booster pump.:)
  10. Ditto......:)

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