Question on pvc pipe size

Discussion in 'Irrigation' started by surge, May 26, 2005.

  1. surge

    surge LawnSite Member
    Messages: 21

    I sent in the measurements to the Toro design team, and the design they sent back called for 1" pipe going to all heads except the drip system. I thought you always wanted to step down the size of the pipe as you go further from the source? Ie The first few heads would be 1" while the end heads would be 3/4". Besides the cost factor of using all 1" pipe vs 3/4", are there any other drawbacks to supplying all heads with a 1" line.

    My specs
    3/4" pvc line going to the house.
    Static pressure 70psi

    For instance, Zone 1 will have 5 340 multi-stream rotors operating at 2.3 gpm for each head.

    According to their design team, they have each 340 roto head being supplied with 1" pvc pipe. Besides price is this a bad idea?
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Oldschool installers and idealist's like me still size pipe. The cost of the extra one inch is offset slightly by not having to have a huge inventory of reducer bushings and 3/4" parts.

    However...with that said, I still bush down to 3/4" for the last 2-3 heads on a line. It allows for easy termination of the line with a female adapter.

    Bic will tell you that if he had time, he'd size it down to 1/2"...but he doesn't :)
  3. bicmudpuppy

    bicmudpuppy LawnSite Silver Member
    Messages: 2,781 'bout a hydraulicly CORRECT system would size down to 1/2", and maybe not even use 3/4, but I don't carry the inventory to install that way on the occasion I do a rigid system. :)
    It doesn't hurt anything to not downsize the pipe except in cost and I'm starting to believe those that claim the cost of fittings exceeds the cost of the larger pipe.
  4. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Do you have any place I could read up on this hydralulicaly correct pipe sizing?
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,070

    I suspect the emphasis on pipe sizing may have had more to do with the behavior of a system with same-sized pipe when first turned on, with the water hammer at the end of the line when the air finished rushing out of the sprinkler. I think modern materials may be strong enough to make the old practice irrelevant.

    I wonder if there is some golf course experience with blowouts at the end of the lines. I know that there are specialty valves made specifically to restrict the flow until the downstream pressure rises above a set point, so there has to be some reason for their manufacture.
  6. Guthrie&Co

    Guthrie&Co LawnSite Senior Member
    from nc
    Messages: 784

    most of the time when you pipe size it creates more friction loss in the system. if the total demapnd of the system is 16gpms at 100 feet you will have 3.37 psi loss in 1'' pr200. in 3/4 pipe pr200 at the same rate of flow you have over 11psi loss at the same distance. so why would you pipe size if you didnt need to? there aresome instances that you need to pipe size but most of the time you dont. plus not to mention all the diffrent fittings you have to buy when you pipe size. it makes a hell of a mess whan you need to repair something
  7. Guthrie&Co

    Guthrie&Co LawnSite Senior Member
    from nc
    Messages: 784

    at 5 fet per second your system will not work properly aith 3/4 pipe. the max for 3/4 at 5fps is 10.1gpms

    1 inch is rated at 16.1

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