Pressure / Flow loss over long run of pipe?

Discussion in 'Irrigation' started by lawnmaniac883, Jun 25, 2006.

  1. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Hi you guys, I am working on a irrigation system for my church. If we could afford to hire an irrigation company to do the install then it would have been done but we just dont have the kind of funds to do that. So, the source is a DEEP well, I believe it is a few hundred feet down and has an inline pump. Not sure how much water it flows, going to see if I can get any literature on it tomorrow but it probably flows an amount comparable to two residential pumps, maybe more and still has lots of pressure.

    Now for the question. We are using 1'' mainline over a run of about 450 feet. The mainline doesnt split off into a smaller 3/4 line or the like. Instead we have 1'' T's with 3/4 threads on them for rotors. What I need to know is how much pressure can I expect to lose over such a long run? Is the mainline going to be big enough at 1''? Thanks.
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    The amount of pressure you lose is directly dependant on how many GPM you will be using with the rotors.

    That said, you should design the system around the MAX GPM output of your pump. If your pump is putting out say, 15 GPM, then use nozzles in your rotors that will consume 15 GPM.

    Using that 15 GPM number, in 450 feet you will be losing 13 or so PSI in 1" Class pipe, change that to SCH 40 pipe and your losing 22 PSI!

    However, even more so important than PSI loss is the speed water is moving in the pipe. The more GPM you shove down a pipe the higher the velocity (in feet per second) is. The general industry rule of thumb is to keep the speed under 5 fps, too fast and you will get lots of water hammer, and possible blown off fittings.

    450' in 1" Class 200 at 15 gpm will be moving at 4.3 FPS...close to the limit, but not over it, if you use SCH 40 you'll be at 5.5 FPS...too fast!

    If this pump is as big as your say it is, you will probably be putting out even more water. I'm going to say that a 1 1/4" mainline is probably not a bad idea:

    1 1/4" class 200 pipe with 15 GPM will lose 3.9 psi over 450 feet and only be moving at 2.7 fps...Much better!

    So, I guess what all this means, is that you need to find out your pumps GPM output first. Then ask this question :)

    Good luck.
  3. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Thanks for the reply, I am definately going to try and get some literature on this pump tomorrow before I bury all of this piping. The morons that were going to dig the trench made it too shallow; we told them to make a 8-10'' deep trench and they only made it 3 - 4 inches...tomorrow I hafta rent a trencher and make a real trench then I can see what kind of flow this pump has. I was concerned that the demand I will be placing over this run may cause water hammer...will post back what I find tomorrow.

    Another question I have is that if I were to change out the mainline and go from say 1'' to 1 1/2 '' and then reduce that back to 1'' at the end of my run just before I start hitting sprinklers, would this be an O.K. thing to do or do I need to have that 1 1/2'' line the entire run of the system? Thanks.
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,764

    Is there some reason you can't just simply run the pump and take some measurements of flow (bucket test) and pressure? Beats the hell out of literature. Then you'll really know what pipe to use.
  5. greenhorn123

    greenhorn123 LawnSite Member
    Messages: 52

    ok I'll ask, are you planning on putting the heads on the mainlne?
  6. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    It is all underground, no spicket to go from. The iron pipe comes out of the ground with a galv fitting on top with pressure relief then goes down to the manifold.
  7. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    I am laying two lines in one trench. One makes up a zone and it is 1'' with rotors and some pop ups on it the other is the mainline which will be going to a valve manifold further up the property. From the manifold will be two seperate zones. So the mainline will not have sprinklers on it.
  8. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Define Rotors and Pop Ups.

    I hope you aren't planning on mixing rotors and sprays?
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,764

    So run a flow-and-pressure test from the manifold. It's all well and good to do slipshod prep work at your own home, but one would think you'd want better for your church.
  10. earlofcrankcase

    earlofcrankcase LawnSite Member
    Messages: 8

    Honestly. You should not ask for info if you cant take the effort to know what you have to build with first. (to me) It seems kind of gay to ask for someone else to answer your question when you won't spend 10 minutes of your time first.

    ( benefit of dought)
    city water = time to fill a 5 gal bucket= gpm
    Well water, let it flow till the pump kicks back on. Do that bucket deal. Then let it keep flowing and test again after the well has run for a while.
    Wells are a good thing but. Like wemen, some are better than others. What your looking for there is a pull down gpm. As the pump draws the water to it. If the table is not large enough the flow will slow down. Main goal with that is to try to have the flow at max sustained output. That way the well pump is not turning on & off. That might take some effort though. So who knows. Keep in mind your building more than their system. (your rep bro)

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