oversize pump

Discussion in 'Irrigation' started by Mowing Mike, Jul 3, 2005.

  1. Mowing Mike

    Mowing Mike LawnSite Member
    Messages: 95

    I dont do irrigation for others but I want to install one at my house. I will have some question from time to time. My first question is is there any problem with getting a laregr pump than you will need? Other than it cost more and cost more to operate. I will be irrigating from a pond, total size 2 acers and total pipe run of 700ft to a hieght of approx 45 ft above pond level. Any other questions you have to help me wll be answered.

    Thanks mike
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    If you get a a larger pump, you need to make sure to use all of the available Gallons per Minute...Otherwise you'll end up cycling the pump.

    With a larger pump your going to need to run a main line large enough to support the extra GPM, as well as have very large zones.

    While on some large properties this makes sense, it doesn't make much on a smaller lot.

    I did a commercial job that was coming off a huge pump (100 GPM, 100 PSI), ended up running 3" main everywhere and had zones with 65 heads on them.

    Of course, theres something incredible about seeing 65 PGP's on at once :)

    EDIT: heres a few pictures of that job just for kicks, I don't have any of the grass area's with the massive zones unfornantly.

  3. Mowing Mike

    Mowing Mike LawnSite Member
    Messages: 95

    Thanks for the reply, I wont to get a pump that will be effective at the end of the line witch is the top of the hill 700ft away and 45 ft high. What harm is done by cycling the pump?

    Thanks Mike
  4. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Cycling the pump is when the pump is producing more water than your system can use, so it reaches its max pressure and the pressure switch shuts it off, then only a few seconds/minutes later the pressure drops low enough to start the pump back up.

    This stopping and starting will burn a pump up very fast.

    I would call your local pump company, and give them three numbers:

    • Length of the pipe run from the pump to your system
    • Elevation Difference
    • How many Gallons Per Minute you've designed your system to run on

    With those numbers, I'm sure they can tell you what pump HP would be best suited, and just for kicks, what size mainline you should run.
  5. Luke in Nebraska

    Luke in Nebraska LawnSite Member
    Messages: 35

    Why in the world would he use a pressure switch, instead of a pump start relay?????????? Think before you speak.
  6. bicmudpuppy

    bicmudpuppy LawnSite Silver Member
    Messages: 2,781

    How 'bout because if you don't put in a pressure switch as a high pressure cut off, instead of cycling them pump and being hard on it, you cavitate the pump and shell it out on the spot. If you don't put a pressure switch on a pump, if as nothing more than a fail safe, then you are the one who isn't thinking.
    Using a pump start does not eliminate the need for a pressure switch.
  7. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    What if he plans on running a hydrant?

    Whats going to turn the pump on?

    Almost every system I install as at least one yard hydrant.

    Think before you speak.
  8. F6Hawk

    F6Hawk LawnSite Member
    Messages: 195

    Harsh words, Luke, and mostly uncalled for. Jon is one of the most respected members on here, and all of his posts that I have read have been spot-on when it comes to giving advice.

    I am but a mere homeowner, not a pro installer by any means (at least not until my current install is done!!), but I have NEVER seen a system that did not have a pressure switch on it. If you messed up in your design, and the pump was too strong for the flow rate needed, what would happen to the pump if you ran the system and it over pressured on a regular basis? IMHO, that would be just as bad as putting the same pump on a pressure switch, it will continually cycle and drastically shorten the life of your pump.

    Or, what if the pump sucked something up and plugged half the heads in a zone? What happens if the pump keeps running with no pressure cutoff?

    On a design note, I think it would be good to have some sort of "bleed" line that feeds back into the pond, that way one could increase the flow until a point where the pump did not cycle at all during on times.
  9. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    Nonsense, I'm but a mere noobie in this field (2 years), but I've done the bookwork, and I am always innovating and improving my style.

    I've seen valves hooked up into the mainline that bled back into the pond that can be actived by flowswitches before, but I've never installed one.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,062

    Such a valve would be a part of any deep well installation, as a backup to the pressure switch control. Depending on the flow rate and mainline size, this might be a two-pressure-tank installation, with one near the pump, with the pressure control switch, and a second one up the hill, serving as a 'shock absorber' for surges and water hammer.

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