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Thread: help with sizing a gravity feed tank pipe

  1. #1

    Default help with sizing a gravity feed tank pipe

    Hello all,
    I am installing a 525 gal water tank 40-50' up on a hill. The tank will flow water by gravity down to a 4 way manifold that waters my garden. The distance from the tank to the manifold is +/- 600'. Can I use a 1" pvc pipe or will that cause too much friction. Are there any other problems that I might run into using a small dia pipe of 1"

    thanks
    JIM

  2. #2
    DIY Senior Member chris8796's Avatar
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    What are the pressure and flow requirements at the manifold and beyond? I would probably be looking at polyethylene for that long of a run.

  3. #3

    Default Reply to post

    Chris thanks for getting back. The requirements are: 20-28 psi from the water tank to the manifold (based on 4.3 per 10 feet of head). From the manifold the switches work down to 4 psi. It is a gravity feed drip irrigation system. I am wondering if 1" tube/pipe might have enough friction to cause a problem. I don't think it will just wanted a true estimate not my WAG. Then comes the cost, pvc 1" is about 150 dollars, it seems that the poly tubing costs more. Let me know

    JIM

  4. #4
    DIY Senior Member chris8796's Avatar
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    You need to have an anticipated flow rate to determine the pressure loss. Most emitters also have a desired pressure (10-20 psi). If you fall below that range, the emitters at the beginning of a run will emit alot more water than those at the end of the run. How many emitters were you planning for each branch and what is their gph? You also need to figure out the pressure loss for the lines after the manifold. Here is a good source of info on irrigation. It also has a pressure loss calculator for the piping.

  5. #5

    Default Thanks

    Chris,
    Thanks again. I am using T-tape. It is a flat plastic tube that drips water. It has a flow rate of .34 gal per min, 20 gal per hour, per 100 feet at 8 psi. I have about 2400 feet of tape. I have the 550 gal tank on the hill that will be constantly filled from the creek. The pipe from the tank to the manifold should have constant 20-28 psi. After the manifold there are 4 timers. There is four zones, each set to water differently. They will be set to run for 1/2 an hour or an hour twice a day (unless rain) on average. So the flow rate if left on is about 489 gal per hour. That is full open. I used the calculator you sent me the link to. thanks. The calculator said using 1" schd 40, 7 gallons per minute, I would have 10.89 psi loss over 600 feet. Going to a 1.5" schd 40 pipe I would have only 1.35 psi loss. So that answers my question. Go with the 1.5 inch pipe. But what about the kind of pipe. Most things I read say use schd 40 and it will last for ever. They also say poly or 200 pipe will not last and is easy to damage. What are your thoughts on that.

    JIM

  6. #6
    Sprinkler Guy Wet_Boots's Avatar
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    As a material, poly pipe will outlast just about anything. It will also withstand soil shifting far better than PVC will, in case you are in a cold climate (this is why one is supposed to include a location when signing up for the site)

  7. #7
    DIY Senior Member chris8796's Avatar
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    If it was mine, I'd do poly (1.25 or 1.5"). I don't have any problem with using sch 40. Keep in mind, most of those recommendations are based on small flat yard, not 600' down a hill.

    Using creek water, use a good filtration system or you'll constantly have problems.

    Check with the local extension agent for watering guidelines for your soil types. Typically, it is preferred to water less often. Air/gas exchange at the roots is typically the limiting factor in plant growth. Depending on the soil type and particule sizes, watering can help or hinder gas movement in the soil.

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