Design question

Discussion in 'Irrigation' started by beocop, May 23, 2005.

  1. beocop

    beocop LawnSite Member
    from VA
    Posts: 10

    Hi everyone,

    I am starting to design my sprinkler system. The water meter is 5/8", main line size is 3/4" copper. According to this, I can only achieve a maximum of 10GPM. I tapped onto the mainline (in the basement before pressure reducer) to lead to two separate 3/4" PVC line locations (left and right of house). My questions are:
    1) If I increase the tapped line size from 3/4" to 1", can I attain the 15 GPM design load? Or am I limited by the 3/4" mainline max 10 GPM?

    2) The incoming pressure (main line) is 65 psi. The pressure I get from a hose bib is only 40 psi (after pressure reducer). Since I will tapping from the main line, should I be designing from the 65 psi or the 40 psi?

    3) How much pressure do I lose if I increase to 1"? Will the new 1" line have the same 65 PSI?

    4) How do I water a strip that is 2' X 50'? The strip nozzles will only do 4'.

    Thanks for all of your help.
     
  2. plow

    plow LawnSite Member
    from nebr.
    Posts: 2

    1) yes 2) yes 3) yes 4) toro 570 mpr 2sst sprays :sleeping:
     
  3. Instant Rain

    Instant Rain LawnSite Member
    Posts: 54

    I will ansewr your questions one by one starting with your question about flow limits.

    Q 1) If I increase the tapped line size from 3/4" to 1", can I attain the 15 GPM design load? Or am I limited by the 3/4" mainline max 10 GPM?

    A Because your main from your meter is copper and you have good pressure I think you can get away with 13gpm safley. you should increase to the one inch line after the tap to decrease the speed of the water in the pvc and depending on the length of the run you may even increase the size farther.

    Q The incoming pressure (main line) is 65 psi. The pressure I get from a hose bib is only 40 psi (after pressure reducer). Since I will tapping from the main line, should I be designing from the 65 psi or the 40 psi?

    A The pressure reducer is there to control the water pressure in your house. I recomend instaling another pressure reducing pressure sustaining valve directly after the back flow. this will give you the ablity to control your pressure, 65 psi is a bit high for spay heads. Don't design by the 65 psi or the 40psi. With a pressure regulator if the brand of nozzle calls for 30 psi optimum pressure then space your heads like they all get thirty psi. Go by the rule of fives when you size your pipe on your zones. up to 5gpm gets 1/2" pipe. over that and go to three quarter. over 10Gpm one inch. And your limit is 13 so unless you have an extreamly long run of pipe thats the largest pipe you should use. If you design your zones ina way that balances the gallons on one side with the other you should be able to get even pressure through out. then you can go back you your dedicated irrigation pressure regulator and "dial in" your optimal pressure with the water flowing. this may require two people with radios or cell phones unless you want to do alot of walking.

    Q 3) How much pressure do I lose if I increase to 1"? Will the new 1" line have the same 65 PSI?

    A It seems you have some idea of the limits of flow and you know alittle about the limitations of your spray heads. I'm surprised to see that you share the common misconception with many other people that increasing pipe size decreases pressure. The fact is inceaseing to the larger pipe will save pressure by allowing the same amount of water to flow at a much slower velocity. this decreases losses from friction and turbulence. Also slower moving water tends cause less problems. Pipe should be the right size for the flow requiered of it. one shoulden't use 1/2" in place of one inch if you had 100psi and you only want 30psi the pressure would only be reduced when water is flowing and it would be very noisy. pressure reducing valves maintain a constant pressure. if the water is or isn't flowing.

    Q 4) How do I water a strip that is 2' X 50'? The strip nozzles will only do 4'.

    A i really don't know of any really good ways to water such a narrow stip. But drip is your best bet. this might require more reducing valves, flush valves and air relief valves. If you don't care about wasting alittle water you cuold just use center strip nozzles turned down some and spaced a bit closer.

    for the most part you seem to be on the right track. one more thing dont cut corners with the quality of parts that are going into it. a few more dollars per valve might be the difference in many hours of maintainance. good luck.
     
  4. beocop

    beocop LawnSite Member
    from VA
    Posts: 10

    Thank you guys for enlightening me. You are all a wealth of knowledge.

    One other question:

    Are toro, hunter, and rainbird spray nozzles interchangeable with each other?
     
  5. DGI

    DGI LawnSite Member
    from SE Mich
    Posts: 173

    Toro etc. are male threads on the nozzle and do not interchange with the female brands you mentioned. I like Weathermatic mists the best. Most forgiving seal.
     
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,035

    Speaking of Weathermatic mist nozzles, they used to make brass strip-spray nozzles for lawn strips as narrow as one foot wide.
     
  7. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Watch it there Boots - you're dating yourself! Use them on the #13 and #33 heads?
     
  8. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,035

    Number 33, natch. I'm no piker. (no adjustable riser, though) Assuming the company still has all their original tooling in good order, they could crank out some more, but without looking at their catalogs, I might guess that the 3-foot wide strip is what they might have these days, if they have any strips at all..
     
  9. bicmudpuppy

    bicmudpuppy LawnSite Silver Member
    Posts: 2,781

    who made (or are they still available) the brass "peanut" nozzles? We used to use them on shurb risers a lot. I was always impressed with the longer radius ones. Seems like 20+ feet was real easy to do with them. They didn't work to well w/ pop ups because they stuck up so high.
     
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,035

    Weathermatic made those, too. When brass was king, WM would sell you any nozzle you cared to order. Want a 60° arc peanut for 16 foot spacing? No problem.
     

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