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RPZ questions

Discussion in 'Irrigation' started by Ira, Jan 8, 2007.

  1. Ira

    Ira LawnSite Silver Member
    Messages: 2,375

    My irrigation guy says I need to switch from my current PVB to an RPZ if I add a polyphosphate injection system for iron to my irrigation system. The system is on a well that also supplies potable water to my home. My zones are sized such that the well pump runs constant putting out 28 gpm at 50psi. The pump pressure switch is set at 40-60. He tells me that the RPZ will eat up some of the water pressure, and I may need to bump the pressure switch to 50-70 to compensate for the loss in pressure. Does this sound right? I heard somewhere else that the RPZ should not affect the water pressure. My PVB is 1-1/2", as the RPZ will be.

    Also, I want to put the RPZ in my well house (8'X14') close to my tank. The irrigation guy says that's fine. What are the chances that my well house ends up full of water due to the RPZ being inside? There is a floor drain to the outside in the well house that can take care of some water.

  2. jerryrwm

    jerryrwm LawnSite Bronze Member
    Messages: 1,274

    The RPZ depending on the size will normally use between 5-8 psi. So if your pump has the capability, you can increase your pressure switch setting.

    To prevent flooding of the well house, you can have him plumb an air gap catch basin below the device and run a line to daylight outside the wall, or even over to the floor drain if you don't want another hole in the wall.
  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,578

    I think that would be 5 to 8 psi loss in addition to what the PVB it's replacing was taking from the system. That leaves you better off than the guy that has to add an RPZ without having a PVB to remove, since most of them will take away at least 10 psi.

    As far as drainage goes, you want to allow for some drips and squirts from the relief, and also, allow for the possibility that a malfunction will have the relief open wide up, and allow the full output of the pump to escape. So if your floor drain isn't up to the task, you could indeed have a flooded room.
  4. Duekster

    Duekster LawnSite Fanatic
    from DFW, TX
    Messages: 7,961

    If you inject anything into the water, you need an RPZ unless you buy a polyphospate product that suitable for potable water. It is out there and you will not use much of it so the cost is not that bad.

    Do you have red water stains?
  5. Ira

    Ira LawnSite Silver Member
    Messages: 2,375

    Even if I bought the potable polyphosphate (which I would rather do), I would probably still switch to an RPZ.

    I don't have rust stains from the irrigation yet, because I've only had the system running for the last couple of months. My water has 1ppm rust, and from what I've heard, that's enough to cause rust stains.

    I've been leaning towards Rid-O-Rust. They have a potable polyphosphate, but they said it would take a lot because of my water's hardness (25gpg). They recommend their Formula 2000 for my situation. I couldn't find any other websites that had potable polyphosphates.

    I think I figured out that I will be using 13,000+ gallons of water a week during the summer to water the equivalent of 1" of rain per week (22,000 sqft of area being watered.
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,578

    RPZ definitely. The whole idea is to take operator error out of the picture.

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