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  • Results 1 to 6 of 6

    Thread: Pump fed vs. gravity fed input/output

    1. #1
      DocJLo is offline Member
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      Pump fed vs. gravity fed input/output

      Hey all,

      I'm drawing up plans on a sort of "all in one" kind of 55 gallon drum filter (for an eventual QT) using a sort of suspended "sieve" that empties directly into the moving bed. Not sure it'll work (I'm using regular wire mesh, not wedge wire; I see a lot of threads with plans regarding this, but haven't seen any followup threads yet, haha) exactly perfectly, but I figure anything would be an upgrade compared to the current pressure filter, both for mechanical and for biofiltration.

      In the envisioned setup (an above ground tank), it would run tank -> pump -> sieve -> MB -> tank. Due to tank size limitations (the tank is 300 gallons, and I'm using a 2,000 GPH Laguna that I've converted into an external pump), I am using 1.25" ID pipe. Using the following table concerning flow rates, I hit a little bit of a brick wall before I start cutting holes and whatnot. The suction side of the pump is 1.25" pipe which - per the above chart - gives it 25GPM/1500GPH. Does this mean that the remainder of the system will run at or below 1,500GPM, as well (since I assume the pump cant pump any faster than it is receiving from the pond on its suction side)?

      The reason I ask this is because I have it planned out that the pond return (MB output) is currently planned to be 1.25" as well; would I need to up the outlet size, or would the 1.25" in outlet be sufficient to prevent overflow?

    2. #2
      BWG is online now Senior Member
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      Use this PVC pipe gravity flow calculator.

      http://www.calctool.org/CALC/eng/civil/hazen-williams_g

      Oversize the recommendation for a safety factor.
      Last edited by BWG; 01-10-2018 at 09:34 PM.

    3. #3
      BWG is online now Senior Member
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      It would be easier to comment if you post a sketch with lengths and proposed flow rates.

    4. #4
      DocJLo is offline Member
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      Quote Originally Posted by BWG View Post
      It would be easier to comment if you post a sketch with lengths and proposed flow rates.
      Your wish is my command! Obviously not to scale. Paint is not my area of expertise, heh.

      Name:  filter idea.png
Views: 173
Size:  59.6 KB

      Edit: By the way, the oval object in the tank is a retrofit BD that I threw in there at some point. The 30" pipe coming out of it runs in the same horizontal plane as the BD, as does the 38" piping up to the pump (square).
      Last edited by DocJLo; 01-10-2018 at 11:22 PM.

    5. #5
      DocJLo is offline Member
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      I haven't hammered out the exact heights yet, but I'm going to assume that the discharge head is less than 20" (the distance from the pump outlet - blue arrow leading to MB - to water level in main tank).

    6. #6
      BWG is online now Senior Member
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      You have approximately 10 feet of 1.25 inch pipe plus a drain and 3 90 degree fittings. 1.25 pipe is restrictive for a 2000 GPH pump. Assuming water is being raised 1 foot plus head loss from suction and discharge pipe resistance, total head loss is probably 4 to 5 feet. This puts your pump in the 1500 GPH range.

      A short 2 inch discharge pipe (no 90 fitting) from the barrel will easily handle this amount with minimal head needed ( 1 inch).

      Very little price difference going up to 2 inch pipe on both sides of the pump and you would gain 200+ GPH.
      Last edited by BWG; 01-12-2018 at 02:36 PM.

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