Aluminium for underground

Discussion in 'Irrigation' started by burlap, Aug 28, 2005.

  1. burlap

    burlap LawnSite Member
    from Indiana
    Posts: 66

    I need to run a 600-700 foot mainline from a well to irrigate my lawn. I have a lot of 5" irrigation pipe. How will that work underground and are there couplings made for that purpose? With 2" PE I will be losing about 3 psi/100' with just 30 gpm and I would like to run more than that. And I can't afford the loss of that much pressure. Thanks, Burlap
     
  2. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    I think you might need to check your friction loss charts again. I checked three different sources and at 30 GPM in 2" PE tubing, the pressure loss is 0.77psi/C'. At 700' you will lose 5.39 psi. If you use SDR-21 PVC 2" the loss is 0.56psi/C'

    The aluminum will have negligible pressure loss due to friction <0.02psi/C'. The problem will be burying the pipe in the soil. The chemicals in the soil will cause the aluminum pipe to deteriorate faster because of the contact with the soil. Plus the couplings are not going to be as water tight as they should be. I have never seen a moveable set irrigation line that didn't leak at most of the couplings after about two seasons. Also with the cost of aluminum you would be better off selling it for scrap and buying PVC pipe.

    Jerry
     
  3. burlap

    burlap LawnSite Member
    from Indiana
    Posts: 66

    Correction noted- I was looking at the velocity column and my chart gives the same reading as yours. However, I would like to pump 90 gpm which means I should be looking at 3' pvc. This would only cost me about 6.09 psi for the run which I think I can afford once I determine my lateral loss. At 90 gpm I should be able to do 3 laterals. I'm still setting up my trickle pump to get pressure and volume readings at the pump. The chart says 114 gpm @ 10' drawdown with 50 psi at the pump. Sounds like my hopes for the aluminium won't work. Thanks, Burlap
     
  4. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,794

    How big is this lawn? There comes a point where its cheaper to buy more valves and a bigger timer than to run 3" PVC.
     
  5. burlap

    burlap LawnSite Member
    from Indiana
    Posts: 66

    The lawn is about 177 x 300 with our house in the middle. I'm trying to make a 35 x 35 spacing with Hunter # 10 rotaries. If figure my laterals would be 177' taking about 30 gpm per run. I would like to figure on about 40 psi for the nozzles. I haven't really worked those details out yet. We use the pump to irrigate blueberries and over the years the flowmeter and guages have gotten to the points where they need to be replaced. Once I know the pump capacity and what it will take to go through the main line, I'll fine tune the laterals. Any suggestions will be appreciated. It's just that I have quite a bit of 5" aluminium pipe I would have liked to been able to use. Thanks, Burlap
     
  6. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,794

    177x300 feet? You don't need 90 GPM for that. Run a 1.5" line, and try to aim for 20 gpm, that would let you run 5 #8 nozzled PGP's for a 360 zone or 10 #4 nozzled PGP's for 180's...Totally adequate for your place.

    Your probably looking at 8 zones or so. A valve is $16. 3" SCH 40 PVC will set you back 10 times that.
     
  7. burlap

    burlap LawnSite Member
    from Indiana
    Posts: 66

    In addition, I would like to be able to get 1'/week. If all this would fall together, I figure I could apply about 1/2" hour. This set up could give me 8 full circle runs and 2 1/2 circle runs. I'm not sure how much irrigating I should do at night. I'm assuming it's best not to have grass wet all night- so I figure I might only have 4 hours in the early moring hours to irrigate-which would be 2 laterals @ 30 gpm. If I can get 60 or 90 gpm time is less of a factor. Thanks again for interest, Burlap
     
  8. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    At 700' from the pump, I sure wouldn't use 1.5" pipe - loss is 9 psi and if you are starting with 50 or so at the pump, you don't have much left if you want 40 at the last head. In fact the loss through a 1" valve @ 20.0 GPM is going to be around 3.5 psi and you still have loss in the laterals to figure also. And if there is any significant elevation change you could be down to around 30.0 psi under the head real quick.

    If the pump will produce 90 gpm, and you are able to run a mainline of 3" PE or 3" SDR-21, (No need to use Sch 40 as the wall thickness difference is not much different and the pressure rating is pretty close also. In fact you could use PVC SDR-26 160 psi and still be safe.) you could run the system in 4 zones. You would need to use 2" valves however. If the pump will only do 60 GPM then you are probably looking at 6 zones using 11/2" valves.

    By using the #10 nozzle @40 psi under the head,(6.0 GPM) and a 35'x35' spacing you will get a precip rate of approx 0.46 in/hr. You would then only need to run the system about 70 min/zone twice a week to get your 1" per week. Using the #8 nozzle(3.7 GPM) your precip rate drops dramatically to 0.29 in/hr which means you are going to have to run the zones at least three times per week.

    So with that, I wouldn't recommend using the smaller nozzles in the heads. Using the #10 nozzles at 6.0 GPM and keeping the system around 20.0 GPM/zone you have now increased your zone count to about 12 or more valves. Using Jon's figures of $16.00/valve - 12 1" valves would run about $192.00. Or you could up the size to 2" valve - 4 @ $48.00 ea = $192.00. That's a wash. So the difference comes in the difference in a 4 zone controller vs a 12 zone controller, and the difference between 700' of 11/2" pipe and 700' of 3" pipe. Personally, I'm gonna spring for the extra bucks and go with the larger pipe. It's probably not going to be much more than $150-$200 difference. Chump change.

    Just my thoughts,

    Jerry R
     
  9. burlap

    burlap LawnSite Member
    from Indiana
    Posts: 66

    I figure a 177' run at a 35' spacing using the #10's would be 4 fulls and 2 half circle at 6 gpm which means 30 gpm per single run. I figure 7 full runs and 2 half runs along the 300' side. At a 90+gpm mainline flow shouldn't I be able to have 3 valved laterals? Thanks, Burlap
     
  10. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Change the half circle nozzles to #8 and you'll be closer to correct precipitation.

    Yes you could run it on three valves. As long as that pump will handle it.

    Jerry
     

Share This Page