Drip Irrigation question

Discussion in 'Irrigation' started by landscaper9929, Jul 15, 2007.

  1. landscaper9929

    landscaper9929 LawnSite Member
    Posts: 54

    I am working on a bid wich will include a drip zone. Only done 1 and it was small and pretty easy, just a few planter boxes, and 2 small flower beds. This one will be a lot different. The area consists of a lot of different plants. Really have a flow question. I know I have roughly 20gpm, but how does that translate into a drip sittuation. What I need to be able to determine is how many zones it will take based on # of emmiters and my flow. Do I figure it the same way I would a rotor or spray zone . Example, 20gpm is my flow rate, a zone with 20 sprays 18 10h and 2 10q's.
    10h gpm=.79x18=14.22gpm
    10q gpm=.39x2=.78
    Total flow is 15gpm for this zone.
  2. Yes only I figure it in hours...

    If you run 1/2 inch drip pipe...rougly 4-5 gpm....would be roughly 240-300gph....add up your drip emitters and their flow and you should be fine.

    I try not to go more than 500 feet or so with drip line..just a personal rule....
  3. landscaper9929

    landscaper9929 LawnSite Member
    Posts: 54

    thanks. So gph is what I am looking for. I was planning on running a 1" lateral and use it to feed the different areas. Can I mix soaker hose with emmiters on the same zone. As for the 500 feet rule I think I will be fine. The area in question runs around a turf area 122'x60', it does not completly surround it though and is only 2-4' deep. Not really sure how many emmiters I will need, I did not count the plants. I am hoping I can figure enough in to cover myself.
  4. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    That is how drip flow is calculated. You will need to covert that to GPM unless all your calculations are in GPH.

    I wouldn't recommend it.

    Keep in mind, I don't believe he was referring to 500 continuous feet. Pressure loss in a 500 ft run of 1/2" PE would be phenomenal. For example, at a flow of 5 GPM you would lose about 50 PSI over 500 ft.

    If your going with drip and not micro, then I would recommend using PE with the emitters already installed. Emitter and line spacing will be determined by the type of soil your dealing with.
  5. drmiller100

    drmiller100 LawnSite Senior Member
    Posts: 562

    one inch poly, or even 3/4 is HUGE pipe to run to the general area.

    then, T off to your drip line. you can basically never have too little gpm with drip. as an example, 5 gpm is 300 gallons per hour, wich is a LOT of emitters.

    I've been using netafin lately, and love it. no maintenance, no leaks when someone walks through the flower bed.
    another GOOD option is to use spray heads with mp's on their own zone. if the plants are tall, you can get tall spray bodies.
  6. First of all...the pressure loss would only be that bad if we were talking about an open ended tube.....I have run 500 foot runs with 100 1 gph emitters inline....and never had a problem w/ flow..

    Keep in mind...on a drip zone you are starting with low pressure anyway....and you don't have "big eaters" sucking away the water and the volume all along the way...

    500 continuous feet is easily done w/ drip......just make sure you use pressure compensating emitters.....

    I wouldn't mix regular drip and soaker hose either..but I have done it in a pinch and it works pretty well....

    Sometimes the hard and fast rules as well as the "never do that" type of stuff gets tossed out the window...and it is suprising how well something you should never do...ends up working just fine...
  7. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    I will have to disagree with this. Ignoring fluid properties, friction loss is directly proportional to flow/velocity of the fluid and pipe characteristics (relative roughness, internal diameter, length of pipe). Absolute pressure does not play into friction loss calculations other than providing a starting pressure in order to determine net pressure loss.

    If the rate of flow through the pipe is 5 gpm (open ended or not), then the pressure loss in the pipe is what it is for that length of pipe.


    Furthermore, those pressure loss charts are normalized (eg laminar flow, constant relative roughness, no elevation changes). As you add more emitters and fittings, the relative roughness changes, and flow characteristics move from laminar type flow to turbulent type flow. This will further increase your pressure losses.

    If you double your emitter count to 250 (1 emitter / 2 feet), and assume a starting pressure of 30 psi, you will have a minimum of ~ 32 psi loss (using the Rainbird PE normalized chart). Once you start figuring in losses due to the emitters and fittings, your probably going to push that number to 40 psi or more. With that kind of pressure loss, you can throw DU out the window and pretty much guarantee that a good number of emitters at the end of that run will barely work, if they work at all.

    PC emitters have a optimal working pressure. For example, RainBird Xeri-Bug PC emitter performance dramatically drops off at pressures below 10 psi. The best operating range for those particular emitters (and drip emitters in general) is between 15-30 psi.

    Long story short, just because your using drip with PC emitters doesn't necessarily mean you can ignore friction loss in long runs of pipe.

  8. Real world answer

    It works......enough said.

    You can toss all the charts and numbers you want at me...I have been installing drip systems this way since early 1992......in the desert of Arizona...

    It works......

    BTW I read the first and the last line of that post...zzzzzzz
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,697

    Reminds me of some discussion about water wetting the (dry) inside surface of a concrete drain pipe. The theory guy claims that a bucket a water poured into the upper end of a pipe would be 'used up' wetting the surface, and nothing would flow from the outlet. Bets are placed, the bucket is poured, and the merest trickle showed up at the outlet.
  10. I hate numbers....I like the real world....and I have seen it a thousand times and performed this magical feat many hundreds of times over.....

    I guess I better go pull all the pipe out of the ground and start over...

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