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RPZ Minimizing Pressure Loss

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

  1. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Messages: 38


    This is my first post and question. The info may be buried in some of these topics already. If so, I apologize.

    I am overhead watering three acres using six zones with 1" pipe and valves throughout. So I have really good pressure. I have a 3/4" inch meter, but I am located almost 100 ft elevation below it - and feed by 1 1/4" supply line. I am amazed at the flow/pressure I can get given this downhill location.

    I need to install a RPZ in order to qualify for agricultural rates. I am afraid it will reduce my pressure and mess up all of the stations and the set up I have presently. I have squeezed just about everything I can out of it now with placement, sprinkler nozzles, etc.

    Question: Is there a RPZ that is known for it's minimal pressure/flow loss? Or would installing a 1 1/2" RPZ be a way to reduce any flow/pressure loss to the 1 1/4" main.

    I know that's a big question from a newbie, and that technically it is not a simple one, with the graphs, gpm, pressure, etc. But I am mainly asking for an opinion about the overall concept of any benefits of over-sizing a RPZ (as to pressure loss), and if any RPZ (1 1/4 - 1 1/2") is known for being the best at minimizing pressure or head loss.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,238

    You must lose at least 10 psi through an RPZ due to the nature of its construction. 15 psi would be more realistic. It is up to you to deal with the loss however you can. Reduce flows. Upsize pipes. Install a booster pump.
  3. hoskm01

    hoskm01 LawnSite Fanatic
    Messages: 5,690

    Like boots said, you'll lose the pressure no matter the size you use, it's the flow you may do better with at larger sizes.

    With the concept in my head of your setup, it sounds like your flow rate has got to be awfully high, through 1" laterals. How many and what kind of heads per zone?
  4. Some Sprinkler Guy

    Some Sprinkler Guy LawnSite Member
    Messages: 167

    Are you currently using a dCA? If so you will probably only lose another 6 or 7 psi going to a rp. Most rp's I am testing will cost you 10 on the nose. But many dcas will cost you 3-4.
    Posted via Mobile Device
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,238

    I recall an old now-out-of-production Zurn design that had a flow curve on the one-inch model that had a sweet spot of 8 psi or so. I think 10 psi isn't conservative enough of a value to design with.
  6. Some Sprinkler Guy

    Some Sprinkler Guy LawnSite Member
    Messages: 167

    The other thing I might do is put the dca at the bottom of the hill so you have more pressure giving a higher flow rate through the valve.
    Posted via Mobile Device
  7. Fireguy97

    Fireguy97 LawnSite Senior Member
    Messages: 394

    Double Check Valve (Dca) or RPZ at the bottom of the hill? I thought that the OP had to go RPZ.

  8. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,921

    Drop some bucks and get the district to give you a 1" meter or bigger.

    No matter what a 3/4" meter can only safely handle 10-14gpm with out going over the rating of 5 feet per second. Which it sounds like you are doing much more then this.

    The biggest useful thing to upsize a pipe from a smaller orgin is less friction loss..
  9. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,921

    Wether the rp is on the bottom of the hill or top of the hill , it makes no difference.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,238

    the flow rating of a 3/4 meter should be 30 gpm (although I'd want a one-inch meter for that high a flow) - a meter changeout might be the simplest way to regain pressure after installing an RPZ

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