Changing my own "rules"

Discussion in 'Pumps and Waterflow' started by RiaanP, 21 Aug 2011.

  1. RiaanP

    RiaanP Moderator

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    Flow rate over a DSB.

    In my opinion, the turnover across your DSB is the real reason why a lot of DSB setups fail. The old advocated rule of between 3 to 5 times your display volume per hour, is not the correct calculation to use. My reason. A sump of 300mm wide will have a different flow rate compared to a 600mm wide sump, when both are using the exact return pump. On exact the same display tank.

    Else, you will have this:
    [​IMG]
    Cayno and detritus settlement. note the extra detritus below the ceriathus.

    Ok, solution, increase the flow rate. My sump is 440mm wide, so I wanted a pump in the region of 5000L/h and economical on the energy. First tried a Sicce Silent, but in an open setup its not silent enough. I eventually settled for the Water Blaster HY-5000W. Although at double the price than the Sicce.
    [​IMG]

    BUT

    immediately run into extra complications.

    The pump push too much water to my display and my overflow cannot handle it.
    [​IMG]
    Bracing touching the water surface.

    [​IMG]
    My cross brace under water. The gunk that collects on the surface cannot get to the overflow.

    [​IMG]
    Can see clearly that the combs are too restrictive. And check the difference between the water level in the tank and the overflow top edge. Removing the combs does help a bit. But the amount of water going over makes an enormous noise. The durso cannot keep up and allows a lot of bubbles to go down into the sump.

    My old solution for bubbles did not work.
    [​IMG]
    Fine Bubbles were pushed out at the bottom. And gave this ugly bubble float that runs across the DSB. The actual problem is the salt spray.

    The next big problem was the level in my return pump.
    [​IMG]
    It used to be 30mm lower than the level over the DSB. Not anymore...

    switching the return pump off
    [​IMG]
    then you can clearly see the volume of water that is now held extra in the display


    So, here are the problems, overflow cannot handle the flow. Return chamber sucked dry.

    What causes these problems.
    The overflow is not wide enough? Water flows to slow down? Return pump too strong?

    But
    the extra flow rate is what I wanted, and I got it. Check to pictures up, see the head of the water going over the overflow. That is about 8mm. Nice strong flow. Cerianthus tentacles are now actually swaying around a bit.

    Solutions. Your overflow MUST be equal or BIGGER than your sump width. With 2 down-pipes, especially if you go to 5000L/h return pumps or more.

    Now the stuff-up. Tank is running and I'm not going to break it down now to do a tank rebuild.
     
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  3. RiaanP

    RiaanP Thread Starter Moderator

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    What I wanted to achieve in the first place was to get a head of water over the last divider in the sump of between 6 and 10mm.

    Congratulations to myself. You did it.

    Realized a new rule that I did not follow.
    Overflow in the display must at least match the sump width, or even wider.
     
    Last edited: 21 Aug 2011
  4. wukkie

    wukkie

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    I don't really agree with you on this statement. I run one of these guy and my sump width is about 600mm, but my overflow is about 300mm. I run 2 40mm pipes from my overflow. This seem to be coping fine, and this has been running for over a year already.
     
  5. RiaanP

    RiaanP Thread Starter Moderator

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    @wukkie, looking at your threads, I cannot find info on your system. Most important, what size return pump do you have? What is the head of water over the last divider in your sump?
    [​IMG]
    see the RO pipe, about same thickness as the head of water going over.

    If your sump is 600 wide. And you have a head of 8mm (like mine above). Then that would mean that your display overflow of 300 should at least have a head of 12mm (if not more). Using combs on the overflow, will exaggerate the head on your overflow.
     
    Last edited by a moderator: 26 Nov 2015
  6. leslie hempel

    leslie hempel Moderator MASA Contributor

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    quick question, why must the flow over the DSB be linke to your return pipe?

    why not place a small pump withing the dsb area? in some situations (as you can see now with your scenario @RiaanP) it is not always possible to go with a bigger pump without hassle..

    am i missing something here?
     
    Last edited by a moderator: 26 Nov 2015
  7. RiaanP

    RiaanP Thread Starter Moderator

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    Yes, Leslie, your thinking... :)
    Yip, one solution is either use another pump to flow directly back to skimmer chamber. Or to split the return line with part of it going to return chamber.

    I know a 50mm PVC pipe, Open and edges smoothed down could handle up to 6000L/h under gravity. That is with no Durso fitted and no ballvalves etc.
     
  8. dallasg

    dallasg Moderator MASA Contributor

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    i thought the flow needed to be as slow as possible over the dsb so that one can create anoxic waters in the deep parts
     
  9. pXius

    pXius

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    Riaan how about a hang on overflow? Not pretty but could solve the problem....
     
  10. butcherman

    butcherman Moderator MASA Contributor

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    Why not put a T-piece on the return and pipe 20% of the folw to the begining of the dsb.
     
  11. wukkie

    wukkie

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    RiannP, I am running the same pump as you. water Blaster 7000.
    I have never checked the height of the overflow. As I said that I use 2 40mm pipes to drain teh overflow and the return pump is using 25mm return pipe.
     
  12. RiaanP

    RiaanP Thread Starter Moderator

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    TOO SLOW, and you get that settlement and cayno.
    Plus it does look like around the cerianthus, its poop is also forming part of the extra detritus on the sand.


    Luckily, on my setup, I got another option. Will show that later.
    I had a DIY overflow pipe construction long time ago when I started with a tank that is not drilled. No ways I'm doing that again. Its a time bomb waiting to flood. Too much hassle to maintain. Been there, done that, no thanks.


    Yes, that is what I did. Re-direct about 50% back to the first chamber.

    The point is, Why redirect it back to first chamber if it could just as well go to the display tank?

    Purpose of this thread is to point out that we do get things wrong. And one error, creates a sequence of events, that together creates a number of problems for us.

    Simple to see, that the water over the last divider and water going via display overflow, is the same volume of water. If I increase the one, then the other will increase. They go together, like salt and pepper. So unless you want a thick head on the overflow, then your overflow must match your sump width, or be more.

    My Durso could handle the extra flow. But it also manage to pull in a lot of air, more than it previously did.

    So in achieving one solution, I created 2 others.
     
  13. dallasg

    dallasg Moderator MASA Contributor

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    while i am anti-dsb's in the sump, i do feel they work better in large deep bins like most setup on RC.
    I am looking at trying a 75L bin filed 3inches from the top with sand, then having a 2cm laminar flow over the top
     
  14. butcherman

    butcherman Moderator MASA Contributor

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    true but you could also run your reactors and ATS orr one pump if you do it right
     
  15. RiaanP

    RiaanP Thread Starter Moderator

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    Anyway, Solution number 2

    All the extra flow of bubbles from the overflow, making a lot of noise into the first chamber. Plus all the salt creep it created.

    [​IMG]

    A 100mm PVC pipe. With end cap. Opened up with dremel so that downpipe fits snugly into it. Downpipe goes down inside about 150mm. 2 small 4mm holes drilled into end cap to allow the air to escape. Basically the same size as my TS2 skimmer lid breathing holes. At the bottom of the 110mm pipe, it is cut at 45 degrees angle to allow the water to flow out and to prevent itself from sealing the flow against the sump base.
    Actually the end cap was the base part of a soil vent valve. The valve itself I used as the Durso. The base as an end cap.

    PROBLEM SOLVED.

    no more bubbles escaping.
    no more noise
    no more salt creep
    :thumbup:
     
    Last edited: 22 Aug 2011
  16. pXius

    pXius

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    Haven't done much research on external DSB's.
    How deep does bacteria penetrate into the sand? This technique obviously doesn't focus on surface area.
     
  17. dallasg

    dallasg Moderator MASA Contributor

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    all the way to the bottom, and mine is 75 deep, it focuses on what a dsb is meant for, anoxic water to break down nitrates to nitrogen.

    search RC for pics and working examples
     
  18. Keanan

    Keanan 2time

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    Was thinking the same thing.
     
  19. Louis Scheepers

    Louis Scheepers

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    @RiaanP I also gave the flow some more thought...

    If the water height above the DSB is 4cm, instead of 20, then the detritus settlement might also change! With a thinner stream of water, there might be more turbulence in the water column, and therefore less settlement. The water height above the dsb might therefore also play a part in determining flow over it?!
     
    Last edited by a moderator: 26 Nov 2015
  20. RiaanP

    RiaanP Thread Starter Moderator

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    Yes, extra pump that flow directly back to first chamber is another answer.
    I went for the bigger pump. And this is the result. But if my overflow was bigger. Then i would not have any issues. The purpose of this thread is to force me and others to think about the overflow size in relation to the sump width.
     
    Last edited: 22 Aug 2011
  21. RiaanP

    RiaanP Thread Starter Moderator

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    Yes could be. @Adee have a shallow water level above his DSB. But where must I put my Ceriathus? Also on smaller systems, the extra water is a bonus. Just ensure that if you do make the water above the sand shallow, then the first divider between skimmer and DSB should also be lowered. Else you would flush the sand directly next to the pane away.
     
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