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Correcting poor head spacing

Discussion in 'Irrigation' started by anotherbrian, Jul 17, 2011.

  1. anotherbrian

    anotherbrian LawnSite Member
    Messages: 21

    I have a 37'x60' area with less than ideal layout of spray heads. The heads are spaced 10' down each line of pipes that span the 60' length. But the widths are horrible:

    +----edge of sidewalk---------------------
    7' of turf with sloping elevation down 1 foot
    +----irrigation line 1-----------------------
    13' of turf with sloping elevation down 1 foot
    +----irrigation line 2-----------------------
    17' of turf
    +----irrigation line 3 and edge of turf----
    landscape plants
    +----edge of house

    My gpm/psi only permits me to use 12' nozzles and so I end up wasting a lot of water and still have troubled areas.

    Through calculation (pressure loss) and by experimentation I have determined that if I eliminate every other head, I have enough capacity to use rotary heads or rotator heads at 45 psi.

    Using 7' of swing pipe, I can relocate the heads on line 1 so that they are adjacent to the sidewalk. Also using swing pipe, line 2 heads can be moved 1.5' toward the side walk. This would result in a near square layout (20'x18.5') which would greatly improve to the existing layout (a mix of 10x17, 10x13, 10x7).

    Does this look like a good strategy or should I just relocate line 1?

    I tried several of Hunter's MP rotators and Hunter's PG Juniors side by side as part of my experiments. It happened to be a windy day and the Junior was much more effected by the wind. I noticed that the PG Junior has less nozzle selections as compared to PG Senior. That makes getting the precipitation rates harder to match the corners to the sides and to the fulls.

    I am curious which would be better for this application or perhaps some other strategy would be better.
  2. DanaMac

    DanaMac LawnSite Fanatic
    Messages: 13,185

    Junior and Senior! Never heard them called that. I like it!
    Posted via Mobile Device

    Messages: 18,668

    I think from a quick glance you are on the right track. Rotors properly spaced beat sprays poorly spaced. Nobody here but me seems to like them but I'm a big fan of Low angle rotor nozzles especially in throws or spacing of 25'or less. If it was me I'd use Rainbird 5000s with low angle nozzles.
  4. anotherbrian

    anotherbrian LawnSite Member
    Messages: 21

    I ended up going with the Hunter Rotator nozzles and got instant results. These two zones are now the best of my 6 zones. It is very easy to fine tune the areas to be watered (e.g., the arch is adjustable).

    The down side is the low precipitation rate - just .5 inch per hour. Our sandy soil here in SE Florida can adsorb 2 inches per hour. The county extension recommends applying .75 to 1.5 inches per watering. So this takes 1.5 to 3 hours per zone. Multiply by 6 zones and you have 9 to 18 hours of watering. During water restrictions we only have a 12 hour time window.

    The Hunter folks suggested running multiple zones simultaneously. This may be possible. Pressure loss is cumulative: a) pressure loss through supply line to point of connection and b) pressure loss beyond point of connection going out into the zone. The gpm rate of each zone is under 1/2 of what was previously used. Thus, the pressure loss through b) is much less than before. The pressure loss in the supply line a) would remain about the same. I need to work through the calculations.

    Pro-C is not programmable to run multiple zones simultaneously. Pro-C can be hardwired so that multiple zones share the same terminal. The Hunter rep recommended using other timers which allow the controller to activate the various zones simultaneously.

    I talked to some of our local suppliers (which are internet based - i.e., global distribution based in Florida). They indicated that a lot of their rotator sales go to Californian and Australia. I found one irrigation installer that uses them here in SE Florida - but that community is under extraordinary water restrictions due to the lack of diversity of water sources by their city.
  5. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    By the book, the PR is around 0.39 - 0.45 in/hr for the rotator at recommended operating pressures. If you are going to guess/round your PR, you should round down.

    Second. if you have an verified infiltration rate of 2.0 in/hr (basically coarse sand), then you have a desperate need to fix your soil.

    Finally, screw what the extension service says .... audit your system and site and determine an appropriate schedule based on real time soil moisture readings and/or historical or real time ET calculations.
  6. jvanvliet

    jvanvliet LawnSite Gold Member
    Messages: 3,944

    Where in SE Florida are you? Have you done a soil test or are you relying on the extensions data? What is your source?

    Bear in mind that S. California, S. Texas, Metro N.Y's, etc. are different environments than S.E. Florida. Their solutions may be different than S.E. Florida's

    I have found in most communities constructed prior to 1987 there is sufficient top soil underneath the turf to reduce precipitation to .75" per cycle and maintain proper hydration at and below the root zone. Most communities after that have had the developers throw the sod directly on top of he coral rock or just a minimal layer of top soil. With these communities, proper hydration is always a problem since the coral is compacted and longer run times create a problem with runoff.

    Again I don't know where you are, but in my area of operation "coarse sandy soil" has not been an issue.

    The area you are talking about is relatively small. If your precipitation requirement is really 1.5" to 2" you are still better off with fixed spray heads than rotors, specially if you don't want to run the water for two or three hours. Rotators are for large areas and tuning them down for small areas can cause over-spray to maintain proper distribution and is bush league (BTW the 1/2" Hunter "JR's" suck, they are not designed to replace fixed spray heads).

    I think 7' is a long run for funny. Maybe your best option is to re-position the laterals add a zone if necessary & replace the nozzles on the spray heads (assuming you are using commercial spray heads & not orbits) to suit the site.
    Last edited: Sep 18, 2011

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