Calculating overflow width

Discussion in 'Pumps and Waterflow' started by RiaanP, 12 Oct 2009.

  1. RiaanP

    RiaanP Moderator

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    Somewhere there was a calculation posted to determine the ideal width of the overflow. Anybody got a link to it?

    A too narrow overflow and the water height above overflow will be too high. Too wide, should not be a problem but who wants an extra wide overflow that takes of valuable display area?
     
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  3. mariusmeyer

    mariusmeyer

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  4. RiaanP

    RiaanP Thread Starter Moderator

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    Thank you,
    Now I got my answer.
    I got a 2880L/h Hailea H-6540 pump. Lift is about 1m, so let me keep volume delivered at 2500 at 1m.
    Seeing the link is to an American site, convert L/h to Gph (US) gives me 660gallon/hour

    Using this calculator:
    • Recommended minimum drain pipe diameter = 1.06 inches
    • Recommended minimum linear overflow size = 10 inches
    Converting that to metric gives me
    • Recommended minimum drain pipe diameter = 26.924 mm
    • Recommended minimum linear overflow size = 254 mm
    I do not have an overflow box, but water enters the 50mm directly.
    The Circumference of a 50mm pipe is 157mm. ( to get the linear length).

    So that is the reason why my return pump is too strong for the overflow. Or why the water level is too high above the overflow.
     
  5. Tim S

    Tim S

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    Hi Riaan, I also have a pipe overflow but have 2 x 50 mm dia. outlets. My return pump delivers about 3000L per hour and the overflow lines (to the 2 outlets) is just below the top of the pipes. If my pump were say 500 L stronger it would start backing up in my tank. Also considdering I use pool pipes after the overflow which restricts the flow quite a bit. So it would seem that one 50 mm overflow is too small.

    Tim
     
  6. RiaanP

    RiaanP Thread Starter Moderator

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    This is interesting, using this calculator, you should be able to use up to 6800L/h flow with one 50mm pipe. I took internal as 45mm. That is a monster flow. But the overflow box must have an linear overflow length of 687mm. Say 700mm. That is a big overflow box.
     
  7. mariusmeyer

    mariusmeyer

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    If you had a 50mm pipe running at full siphon you could probably push more water than 6800LPH through it. It can handle a hell of a lot of water.
     
  8. Reef Maniac

    Reef Maniac MASA Contributor

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    The flow over a weir (or pipe end...) is influenced to some extent by the radius of the weir "lip" - if the top of the pipe is flat (as sawn off) and the edges at 90°, the sharp edges will induce drag, and can restrict the water flow by up to about 40%, compared to a rounded, smooth edge profile. So, to increase water flow over the "weir" without any major change in plumbing, just round the edge of the pipe...

    A quick calc using a 50mm diameter pipe, and a water head of 10mm, gives a flow capacity of 1882 liters per hour over a sharp-edged pipe, and a flow of 2944 liters per hour over a smooth, rounded aperture. A head of 20mm nearly doubles these capacities.

    Hennie
     
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