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RPZ Minimizing Pressure Loss

Discussion in 'Irrigation' started by dypsisdean, Sep 4, 2010.

  1. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,595

    To the top. :hammerhead: Thread is dead.
     
  2. Some Sprinkler Guy

    Some Sprinkler Guy LawnSite Member
    Posts: 167

    He can't put it at the bottom anyhow but the last time I checked flow rates increase at higher pressures. If I am mistaken, please fill me in. I learn something new everyday.

    Will the gpm flow be the same at 85psi as 120psi?
    Posted via Mobile Device
     
  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,429

    Is a light bulb brighter at the bottom of the hill?
     
  4. Some Sprinkler Guy

    Some Sprinkler Guy LawnSite Member
    Posts: 167

    Depends where's the transformer? :).
    I really am interested to hear a factual response. Every flow chart I have ever looked at on backflows shows the flow rate increasing with pressure. So in a situation where you were trying to maximize flow it might be more of a restriction when placed at the top of the hill where the pressure is lower.

    The pressure on the line will remain the same regardless of where it is located.

    It sounds to me that his system is terribly overflowing the 3/4 meter, so my point of higher flow rates is valid in a maximum flow condition.
    Posted via Mobile Device
     
  5. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,595

    ....................:dizzy::dizzy::dizzy::dizzy:
     
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,429

    Build a diagram and try to display this concept.



    Good luck.
     
  7. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Posts: 38

    Well, you sure know how to make a new guy feel welcome. So before you chase me out of here, I just have to say you are wrong. (I know, an impossibility in your mind)
    A Maxi-Paw, and most impacts I know of, need a pressure of 25 psi minimum. And they don't work all that great at the lower pressures anyway. The non-popup Hunter PGP I am using is working well at the working pressure of 15-20 psi that I designed for in order to assure I don't blow apart the compression fittings used for the thin walled polypipe. Since limiting the pressure to 15-20 psi, I haven't blown any fittings (at 25-30 psi I occasionally did). This non-popup Hunter gear driven rotary sprinkler/nozzle combo I am using works like a dream at the lower pressure, regardless of what the specs indicate. By placing 15 of these sprinklers on a zone, the working pressure is safe for the compression fittings, yet adequate for the sprinkler's operation - a nice balance. Something impacts could not accomplish at 20 psi.

    With close to 500 compression "joints," and watering at night, I couldn't risk the possibility of blowing apart a 1" compression fitting, because one zone needs to run for 4-5 hours to equal 3/4-1" of rainfall. An open inch line for 5 hours would be wasteful to say the least.
    With 30 years designing swimming pool circulation systems you gain a feel for how hydrodynamics function. You also learn that using and depending on all the flow charts from manufacturers, and all the technical equations, may work well in the lab and classroom. But in the field when there are often some unique applications, the "feel" of the professional is often better than pencil and paper. But I never dealt with RPZs in a closed system. So that is why I came here asking advice. The three plumbers (professionals) I had look at this situation all gave me different answers.
     
    Last edited: Sep 5, 2010
  8. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    You might start by learning how to read a graph.

    Sounds to me like you can't do the math, nor would you know what to do with it even if you did know how to do it. Fact of the matter is, you need to know your flow if you want an answer to your question. If you can't figure that out on your own then hire someone who can.

    And FYI, I have probably forgotten more about hydraulics and system design then you will ever know.
     
  9. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Posts: 38

    You're right - the RPZ has to be within 5 ft. of the meter.

    I believe the answer would depend on the amount of head encountered. And that is exactly why I was questioning whether my unique straight 100 ft fall between the meter and valves, and almost zero head (maybe even a negative) would alter generally accepted knowledge about the restrictions in the RPZ. I am certainly "pulling" way more water through the 3/4" meter than many would think possible.

    And BTW - thanks for all the comments from those who actually tried to offer constructive advice in a cordial manner.
     
  10. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,595

    Any time we can help. :dizzy:
     

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