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Thread: How does a bottom drain work?

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    uunfews is offline
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    How does a bottom drain work?

    Look at the link to the diagram I posted. If pond crud and fish poo are heavier than the water how would it rise from the drain line and be trapped in your settlement chamber? Just doesn't make sense. In a toilet you have water pressure since the water line from the initial flush is higher then the sewer line. In a pond both the settling chamber's water line and pond water's line are at equal elevation and hence there is equalization. Less you stick a pump on the line in between the settlling chamber and the pond with a heavy enough suction force then you can move the crud into the chamber but you would be grinding that crud up same as if you had put a pump directly into the pond.


    http://www.koicarp.net/pond_construc...n_diagram.html

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    It works because of the velocity of the water. A toilet is only moving a few gallons.....a drain is pulling about 3500 gallons per hour thru it. When I built my pond, I got a lot of sand in there. Believe it or not, within a week, all the sand had gone down the drain and was dumped out of the filter.

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    Like a shower drain


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    IN the diagrams you posted the pump is pumping water out of the settlement chamber. SInce the two bodies of water are connected and will always try to equalize, the water from the pond rushes out the bottom drain to replace what is being pumped out. This is done continiously.....

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    Your sediment chamber has an exit, usually also 4" PVC, it is located below water level or many have it in a slotted pipe protected with a micro-screen, the heavy solids settle in the tank bottom,but water is flowing in and out at all times. That is why a larger tank is used to keep the water in the vortex longer for waste to settle out. You will also have a drain in the bottom of the tank 4" also with a knife valve it is closed during operation, but to flush the crud to a waste site or garden, you shut the system off and open the knife valve, to flush the toilet so to speak. You also just did a water change since new water must be added to top the system back off.
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    Thanks everyone.
    Ok so I understand now. If it works on the velocity and water displacement principal, then I must have a certain velocity created for it to suck up the gunk collecting in the drain pipe leading to the settlement chamber by the use of a pump. How would I go about sizing the pump and piping size then to create that velocity? Is there a formula or a link(s) to explain how to set up such a system for efficient waste removal?

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    CarolinaGirl is offline
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    Quote Originally Posted by uunfews
    Thanks everyone.
    Ok so I understand now. If it works on the velocity and water displacement principal, then I must have a certain velocity created for it to suck up the gunk collecting in the drain pipe leading to the settlement chamber by the use of a pump. How would I go about sizing the pump and piping size then to create that velocity? Is there a formula or a link(s) to explain how to set up such a system for efficient waste removal?
    a 4" drain needs to flow about 3000 to 3500 gallons per hour. If it does not flow enough, the entire drain line acts as a settling chamber and stuff will dit in there and decay. If you have a small pond and don't want to flow 3500 gallons per hour, then it is far better to use a 3" line and a smaller pump, rather than use a 4" line and not flow enough water to keep it clear. Don't bother with a 2" line. It will not gravity flow enough water to be worthwhile. So bigger is not necessarly better....sizing the bottom drain line depends on how fast you will be pumping water out of your settling chamber.

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    I know you got your answer but I thought I would state it another way, at 3500 GPH, a 4" pipe will flow at about 1.43 feet per second... How does the stuff not just settle in the pipe? Think about the pipe as a vacuum, it doesn't have a chance to settle. As CG said, there is a point at which the water velocity in the pipe is no longer enough to keep the solids in suspension, however if you are doing regular water changes by dumping your vortex chamber, you can purge the lines of detritus by closing the valve on the bottom drain line, dumping the vortex, then opening the valve, just about everything stuck in the line will be removed by doing this... Just an option if you go too big with the line. The rule of thumb is that you want 3000-3500 GPH for 4" pipe, about 2000 GPH for 3" and 750 GPH for 2"
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    pond term "gravity flow" or "gravity" or "gravity feed" terms get mixed around. basicly what the others have already stated. displacement dealy

    nearly most all of the time bottom drains out there are piped to a settling chamber.

    gravity flow pipe sizing normally is large size pipe. than the pipes that are connected after the pump. vs pipes that are before the pump.

    like Carolinagirl already stated about sizing. others may simply state larger size pipe the better. if ya go to small ya normally in for a headache and trouble. to small = complete tear up of pond and redo plumbing to make pipe size bigger. if ya go to big, it can be delt with. with flushings that are normally ease to do, and done anyways.
    Pond and Construction Forum 101 good place for any first timers to the forum. for finding resources and general info.

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    Dan: I want to know how do you come up with the velocity for a given pipe size? Is there a chart? I take it the rule of thumb you stated '3000-3500 GPH for 4" pipe, about 2000 GPH for 3" and 750 GPH for 2" ' is the pump rating per hour? Would the velocity of 1.43feet per second be the same then if I was to match up GPH to pipe size? What about 500GPH to 2" pipe??

    CG: I was thinking of 2" pipe . Not clear still on what you mean not enough flow in 4" pipe and then also not 2" pipe but okay with 3" pipe. Wouldn't the smaller the pipe the faster the velocity assuming same pump size?

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    The rule of thumb I think I got from Steve C.
    As I understand it, it is based on how much flow you can pull through a pipe from one chamber to the other (pond to vortex, or barrel to barrel), with minimal (less than 1/2") draw down. Draw down is the water level differential required to get a certain flow through the pipe under gravity feed.
    For instance if you are pumping 3000 gallons an hour out of a vortex and only have a 2" pipe feeding it from the pond, the pump will draw the water level of the vortex down a little over 5" before the pressure differential reaches an equilibrium... but if you were only pumping 750 gallons/hour out of the vortex, the pump would only draw the water level down just over 1/4". The draw down of 5" may not sound like much, but if you are going through a string of a vortex and barrels, the last barrel would be drawn down over 20"!

    I use the calculator on the following site for my numbers: http://www.efunda.com/formulae/fluid..._tank.cfm#calc
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