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Thread: Flow Rate Using a 4" Bottom Drain Pipe

  1. #1
    Oyagoi yerrag's Avatar
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    Flow Rate Using a 4" Bottom Drain Pipe

    In a gravity flow system, what is the max flow rate going thru a 4" bottom drain pipe? I've wondered about my own pond, which I feel is constrained by the flow rate limits of the 4" bottom drain. Flow rate is at 5000gph, but it can't handle twice the rate.

    There seems to be a formula for this, but I forgot about it.

    My filter is far away from my pond, and I believe the length of my bottom drain pipe causes friction losses which in turn limits the flow rate more.

    Add: I also have 2 3" skimmers, which I forgot to mention.

  2. #2
    MCA
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    Honmei MCA's Avatar
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    The flow rate is driven by pressure difference at the source versus the end of the pipe. For gravity fed, that means the height difference between the two end of the pipe. The greater the height difference the greater the pressure. Fighting against the flow is the pipe resistance from the type of pipe (i.e. plastic, cast iron), the length of the pipe, and the number and type of fittings.

    CalcTool: Gravity-fed pipe flow calculator

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    Oyagoi yerrag's Avatar
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    Thanks again Mike! If I wanted to allow higher flowrate in my pond, the simplest thing would be to increase the drop (which is the difference in water level between the pond and the filter). This would be a relatively easy thing to do, by lowering the level by which water is allowed to exit a chamber through transfer pipes. If this level is set too high, at a high flow rate water is not allowed to pass through to succeeding chambers, and as the pump continues to operate, the water level at the chamber where the pump is pulling water from becomes so low that it will cause the level switch to turn off the pump.

    At least I know I can still tweak my filter to allow for a higher flow rate easily. A higher flow rate may be in the cards in the future, and I know I am not constrained too much physically.

  4. #4
    Sansai
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    Bottom drain, flow rate

    Quote Originally Posted by yerrag View Post
    Thanks again Mike! If I wanted to allow higher flowrate in my pond, the simplest thing would be to increase the drop (which is the difference in water level between the pond and the filter). This would be a relatively easy thing to do, by lowering the level by which water is allowed to exit a chamber through transfer pipes. If this level is set too high, at a high flow rate water is not allowed to pass through to succeeding chambers, and as the pump continues to operate, the water level at the chamber where the pump is pulling water from becomes so low that it will cause the level switch to turn off the pump.

    At least I know I can still tweak my filter to allow for a higher flow rate easily. A higher flow rate may be in the cards in the future, and I know I am not constrained too much physically.

    Buy a drain cleaning nozzle for your high pressure cleaner .Fit to the end of your hose.Put your cleaner on the highest pressure and feed it down the bottom drain pipe, blasting the internal walls scouring and dislodging all the gunk stuck to the pipe wall.
    This gunk helps to create a resistance and lower the water volume.
    Feed up and down a few times, this should dislodge most of the gunge. Pull the pipe out
    Fit your stand pipe in the drain socket in the settlement tank. Put your pond pump on and empty the settlement tank. Switch off the pump.
    Lift the stand pipe and the inrush of water should drag all the gunk into the settlement tank were it can be drained away.
    Repeat if necessary.

    Cheers

    Garfield

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    Oyagoi yerrag's Avatar
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    There's actually no need to call the SWAT if there is peace and order:-)

    Sent from my XT1068 using Tapatalk

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