Low Pressure

Discussion in 'Irrigation' started by Dirt Boy, Sep 27, 2006.

  1. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    I installed a system and thought I would have enough pressure, now that I have it buried, things aren't working so great.

    well supply - 27 gpm (supply for sprinklers T's off from 1" mainline, then continues on to building & pressure tank/switch reg. 40-60psi).

    Irrigation - 1" (less than 10') to filter/MV (1"), then to 2" mainline supply. 2" line is overall aprox. 500' lg. with 1" risers coming off at various locations to supply zones.

    Zone supply - fed from 1" (off 2" mainline) thru mainfold (not sure of the brand name, but they screw together - O Ring seals, etc. Dura?) feeding 1" valves.

    Laterals - Utilzed 1 1/2" lateral lines (some runs as long as 250' total, most at 125') using "blazing saddle" connectors to funny pipe, to K Rain Super Pro rotors.

    What I have done - measured output several times during construction with my "flow meter" (which consists of several heads and pressure gauge mounted on a manifold) thus I was able to connect to the 1" risers, turn on water supply, activate as many heads as needed to keep pump running at aprox. 50-55psi (inside building pressure switch). I ended up having aprox. 27 psi of pressure and running 25 gpm. This was measured without zone valves in place.

    So, I put 5 heads to a zone, and now with everything installed, my pressure has dropped (I need to measure it). Consequently, things look poor, even the runs that are closest to the supply (less than 50' of mainline, 125' of laterals).

    What should I be looking for?, besides execuses?

    Thanks a bunch guys/gals!
  2. PurpHaze

    PurpHaze LawnSite Fanatic
    Messages: 5,496

    Hmmm... First thing I note is that you're running 27 GPM through a 1" pipe which EXTREMELY exceeds the GPM for 1" pipe. Causes excess friction which reduces overall pressure.

    Without being there and seeing exactly how everything is routed would just be conjecture.
  3. SprinklerGuy

    SprinklerGuy LawnSite Bronze Member
    Messages: 1,778


    I think it is pretty obvious...I will give you the laymans terms...and someone will be by shortly to use all the formulas and garbage to explain the same thing... :)

    You are trying to fill a 2" mainline with 27 gpm? 500 feet of 2" mainline as well.....let me guess, I it is also uphile 200' ?

    That is like trying to piss out a 200 acre fire.....
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,410

    Easiest thing to try is to rip out all your one inch stuff and replace it with inch-and-a-half - but a one inch backflow preventer can remain in place, since these share the same flow capacitites as water meters.
  5. speedbump

    speedbump LawnSite Member
    Messages: 117

    I'm curious how long you ran your flow meter? Could be the well is pulling down causing that 27 gpm to be much less which would directly effect the pressure as well.

  6. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    -No, it's not 200' uphill (do I detect a bit of sarcasm there:rolleyes: ) it's slightly downhill.
    -Mainline is always full of water, so it's not like I'm trying to fill it every cycle.
    -Yes, velocity of 27 gpm in 1" pipe is approx 10'/sec, but total length of 1" pipe would only be about 6', so pressure loss should be less than 2 psi.
    -I ran my test fixture for 10 minutes or so, no other water being used, let system stabilize, so pump was running constantly, pressure at inside pressure switch at 55 psi and let it run long enough to know that it wouldn't be switching on & off.

    The supply line running inside building is 1" and plumbers put 1" tee in for me. So, perhaps I screwed up thinking 1" risers were sufficient (hindsight, it would have been just as easy to keep it big all the way). 1" valves for system, rated to handle 35 gpm (5 psi loss).

  7. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Why not make it a full 2'' run all the way. Make the manifold out of 1 1/2'' then use 2'' for the rest. Why add restriction when you can avoid it?
  8. YardPro

    YardPro LawnSite Gold Member
    Messages: 3,570

    2" main has nothing to do with the flow/pressure loss...
    larger pipe wil maintain the pressure better by having less velocity thruogh the pipe. It's called bernoulli's principal...

    27 psi is not good pressure at all.

    most pop up's will not even pop up in the low 20 psi range.

    you should zone it out to have at a minimum 35 psi.

    next is what type of heads are you using.. nozzle size, etc...

    also i agree with the well pump down idea.. this could create a lot of problems.
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,410

    Dump the "test fixture" ~ if you're going to take people's money, get some real measuring tools. :hammerhead:

    Do you have a backflow preventer on this system?

    When you exceed 25 gpm, you can gain some performance (by way of lower pressure losses) by moving up to inch-and-a-half valves. By the way, a one inch spindown filter has a pressure loss high enough to make it worthwhile to bump it up a notch in size.

    Of course, if you are only seeing 25 psi, on the well tank gauge, that means you could reduce zone gpm and gain more pressure. Start changing out nozzles. By the way, ten minutes of runtime tells you very little about a well. I've seen wells take over an hour to run dry at normal pump flows.
  10. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    It's a new well, so I'm confident that it's working properly, and not being drawn down too much.
    Right or wrong, I have my nozzles sized at 5 gpm, so theoritically that should work out to 25 gpm.
    Pressure switch is reg. 40-60 psi
    My test fixture, while perhaps not "professional" should give an accurate indication of performance. I can turn on as many heads as needed, which I have set up with different gpm nozzles.
    I need to check some pressure readings in a couple of places, probably remake the manifolds out of larger pipe, try a few other things.

    But Hey! it's raining nicely, so screw the sprinklers!!! not really

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