step down pipe

Discussion in 'Irrigation' started by LemkeLawns, Aug 13, 2008.

  1. LemkeLawns

    LemkeLawns LawnSite Member
    Posts: 81

    guys, I am working on a new install and was curious as to when a person needs to step down in pipe size. I'm not necessarily looking for a specific case scenario but rather a way to calculate when to step down and how drastic of step down. Any help would be greatly appreciated!!
     
  2. Dripit good

    Dripit good LawnSite Bronze Member
    Posts: 1,081

    From what size, to what size?
     
  3. LemkeLawns

    LemkeLawns LawnSite Member
    Posts: 81

    is there a general formula used to determine when to step down?? Id like to apply the formula to different situations in the future so im not wasting every ones time by saying im using pipe size A when should i switch to size B and im going X distance with Y psi and Z flow
     
  4. Waterit

    Waterit LawnSite Silver Member
    Posts: 2,906

    Look in rear of Rainbird catalog for pipe-sizing charts, then add up your GPM as you add heads to zone.

    Or take a class at your local distributor to get some knowledge before you start installing. Your question is very basic knowledge for any installer, makes me wonder what else you don't know about this game. Not being nasty (well, a little), just saying that like anything else, having a clue about what you're doing goes a long way towards doing it well. And that's what it's all about.
     
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,357

    If you are going to step down from one-inch to 3/4-inch pipe in a line of heads, a good general rule is that you can feed two 3-gpm rotors from 3/4 pipe without excess pressure loss.
     
  6. evergreensolutions

    evergreensolutions LawnSite Member
    Posts: 55

    IN GENERAL......GPM for all heads downline dictates pipe size. You do not want to exceed 5 fps for the given pipe size or you increase chances of water hammer. Flow Charts are your best friend when designing a system. "General Rules" are different for everyone. Someone might be comfortable with a little more velocity than me. Comes from experience.
     
  7. Dripit good

    Dripit good LawnSite Bronze Member
    Posts: 1,081

    Waterit nailed it. Take a basic course and refer to the pipe charts. My sugestion is don't reduce your laterals less than 1". Too many parts to buy and stock for no real good reason.
     
  8. LemkeLawns

    LemkeLawns LawnSite Member
    Posts: 81

    thanks everyone! Ill b the first to say that im ignorant when it comes to irrigation. I see it as there isnt any harm in asking before a project, but there is a ton of extra work if a system that is put in wrong and has to be redesigned and reworked. I have learned a ton from my rainbird and hunter catalogs over the last week including info about nozzle sizing, psi loss, under zoning systems, and the list goes on. thanks guys
     
  9. Waterit

    Waterit LawnSite Silver Member
    Posts: 2,906

    You're on the right track, you recognize that there are things you don't know and seek knowledge. Journey on, Grasshopper!
     
  10. LemkeLawns

    LemkeLawns LawnSite Member
    Posts: 81

    The reason I decided to start installing irrigation was b/c it cost me $360 to replace a golf head that we hit on a football field we mow. I worked under an IA member at a local university and knew that if the installer knew what the f he was doing, his heads wouldnt have been set above grade and sheered off with by my mower. Then this week I ran into his work again on a volunteer install job at a sports complex. He shows up and starts rattling off theories of what a person could do at the site and that there are 100 different ways this system could be installed.... he took absolutely no measurements, didnt check what kind of flow or psi the booster pump is putting out. There is an existing system on a baseball field and two additional practice fields will be ran off this same pump. I thought this would be an excellent time to increase my knowledge on psi and friction loss. I have found that this guy's design will yield a velocity greater than 5ft/s in the main line and in order to have 1 inch of precip. the system will need to run for 32 hrs. The system is capable of 77 gpm and is measuring 70 psi on the baseball field. This guy will only be using about 35 gpm per zone on the new system. When I mentioned that he had absolutely no clue on what the pump was putting out, he replied "it works over there so it will work over here.":wall
     

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