RPZ Minimizing Pressure Loss

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

  1. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Messages: 38

    Yes I did. It's hundred year old trees (100 ft tall) and forest that has grown on top of this type of lava. I've planted 1000+ rare plants in trees in and among the forest. I was just trying to show why trenching and rigid pipe wouldn't work very well. :)
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,758

    And still we don't have the flow numbers for the zones. Does someone need an engraved invitation to open a zone and take some meter readings for a fixed time interval? Guesswork and estimations very much do not cut it.

    And why can't all the heads be re-nozzled? 3 gpm nozzles would be PGP #7 - replace them with #6

    And take pressure readings. Connect a gauge and read the number. No %^&$*# guessing!!

    If you are so in love with the existing arrangement that you will never change even one nozzle, then install a booster pump to regain the pressure lost in the RPZ.

    For an ag setting where you want to stretch a water supply to the max, the way to go is wedge-drive impact heads. Compared to a 3 gpm PGP, even the humble Rainbird Maxipaw impact head could do more with less.
  3. 1idejim

    1idejim LawnSite Fanatic
    Messages: 11,358

    i was asking about the rare frigging plants, you obviously didn't plant the 100 year old trees, so you're supplementing them as they lived this long on their own.

    you have given the parameters in which you will required to work, you have received some good advice that you seem to discount.

    this is not about trenching and rigid pipe, it's about flow, pressure and trade offs.

    in order to get an ag rate you need to install a rpz, you have to hire a lic. plumber to install the rpz, you don't want to install a booster pump because of electricity.

    you have about a 40 psi gain from elevation change plus the working pressure of the supply @ ???????????.

    you have a pressure loss of ???????????????.

    you have a velocity of ?????????????.

    you have working pressure @ heads of ??????????.

    you have a flow of ???????????? @ the main.

    you have a working pressure of ???????????? @ the first and ??????????? @ the last head of each zone.

    answer the above ???????????? and it will make things easier, the other choice is to "grip it and rip it" (tin cup) :)
  4. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,174

    Jim and Boots are asking the right questions and their advise should be taken (or hire a pro). I understand Hawaii has some of the most stringent backflow regs in the country; good for them. :clapping:
  5. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,335

    The plots are simple if you know your flow rate. If you don't know your flow rate then you are pissing in the wind. If you don't have much pressure to play with and you have deep pockets then continue on as you have been and just hope your guess works out.

    That said, if you want to work on assumptions only, then assume you will lose 15 PSI by introducing an RPZ into the system. If that is going to break the system, then consider yourself screwed without a booster pump.
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,758

    maybe he can get a lava-powered booster pump :)
  7. rlpsystems

    rlpsystems LawnSite Senior Member
    Messages: 472

    Man, great coffee and surf. Just watch out for Jack Johnson and Dog!!!
  8. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Messages: 38

    I didn't expect to be able to relate all the variables accurately and in a fashion for everyone to understand this different type of set up. That's why I began by asking only about the reduction in pressure/flow/head using an RPZ given the uniqueness of the system due to the extreme "fall" of the water from the meter and the oversized supply line. It seems to make a tremendous difference in the hydraulics involved. And then further asking if the size or make of the RPZ would make any difference.
    I thought I explained that this would not be the preferred solution since the next nozzle size down (to Hunter blue #2.5) from what I am currently using would reduce the "throw" distance by 3 feet. (Currently using Hunter blue #3.0) The next size down from that would be even more. My spacings are such that such a reduction will probably leave some dry zones. I could not place all 90 sprinklers exactly where I wished due to rocks, trees, roots, etc. Please understand that each sprinkler required jackhammering a hole then cementing an eight foot tall steel rod in the hole to attach the sprinkler at the 6-8 foot heights - or tying to a strategic tree for support. But of course that would be the first remedy if the system "choked" after the installation of the RPZ. But I was trying to avoid that.

    I can not take pressure readings at the meter - 2-3 feet underground and covered with rock for over 500 ft. to the house. This is the only pipe, along with electrical service that was installed underground with very heavy equipment. Readings at the sprinkler valves is about 120 psi - it varies. Figuring flow rates, velocities, etc will not be relevent because I am not installing a new system. I was only trying to determine and predict what adding an RPZ will do to this one. At this point, I really don't think an accurate prediction is really possible. I was only asking.

    What I am having trouble getting you guys to understand is that:

    1) I had to use polypipe.
    2) Because of that, and the compression fittings ratings (low pressure), I had to keep adding sprinklers to a zone until the pressure in the line (while in use) was reduced enough not to "pop" the fittings - while using a sprinkler and nozzle that would still work given that greatly reduced pressure - and still spray 25-30 ft. from 6-8 ft risers.

    I didn't expect you to really understand a "pressurized system" using polypipe. It is not designed for that - only micro sprinklers and drip. I had doubts whether I could even make such a system work. But as mentioned, it has worked perfectly without a hitch or leak, with the first zones now 8 years old. If I had the RPZ from day one, the system (spacing, nozzles, placement, etc.) would all be working perfectly and designed for that, with a different configuration. I didn't anticipate eventually irrigating all 3 acres and applying for the ag rate eight years ago. I was only hoping someone could help to mitigate the addition of the RPZ, and/or offer advice as to what to expect after I did. Installing a new system, or booster pumps would not be cost effective. However, if I can't make the system work with the RPZ, then a new meter would probably pay for itself in about 4 years.
    Last edited: Sep 5, 2010
  9. dypsisdean

    dypsisdean LawnSite Member
    from Hawaii
    Messages: 38

    Sorry for not making myself clear. The irrigation is to supplement the rare plants and trees that are placed in, on, and among the many native trees that are here. Some of the extremely rare and endangered species I am envolved with cannot survive on the natural rainfall here. In addition, we had a 50 year drought here this dry season - virtually no rain at all. So while many neighbors lost a large portion of their native ferns and many of the younger trees, I did not.
    I have greatly appreciated the feedback, and everyone's willingness to offer it. However, this is about the pipe, fittings, (and it's pressure ratings), I had to use and the constraints, considerations, and the adaptations I had to consider to make it work. (I explained in the post above) I doubt if there is another system as extensive designed as such. That is why a professional would laugh and claim it as unworkable. But it has proven to be a great solution. It is only my desire to now try and utilize an ag rate and the subsequent requirement for the RPZ that has thrown a wrench into my perfectly working system.
    Last edited: Sep 5, 2010
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,758

    Stop thinking you have a "very special situation" ~ your ego will survive. Hunter PGP's with blue nozzles are hardly the last word in watering efficiency. Impact heads like a Maxipaw will spray further at lower pressure and with less flow and with better distribution. Wedge-drive impacts can do even better, as long as you only need full-circle heads.

    If you actually bothered to diagram your system, and take the appropriate measurements of flow and pressure, you wouldn't have to play guessing games.
    So how the $%^&*#@ do you plan to read product performance charts if you don't know your flow rates?
    And whatever misconceptions you possess about poly pipe, {hilarious epithet deleted}. We understand more about this stuff than you will ever know on your best day on Planet Earth.
    If you don't know the flow rates, how the %^$#@& can you determine whether a larger meter can help?

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