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  • Results 1 to 14 of 14

    Thread: I'm buying an external pump for my retro BD but the waterfall pump is concerning me

    1. #1
      bart is offline Member
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      Question Does the return waterfall pump have to = the external pump attached to retro BD?

      I'm buying an external pump that will be attached to my retro BD but I'm afraid if I buy a pump that's too powerful it'll overflow the filter barrels because the return waterfall pump is smaller and has to go up like 6 feet with a couple of right angles through 1 inch pipes, which I understand slows it. It empties the barrell quite quickly though (and has a float switch ).
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      Last edited by bart; 1 Week Ago at 09:41 PM.

    2. #2
      DragonFireSG is online now Senior Member
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      Putting any pump behind another pump is generally something to be avoided.

      Without an elaborate array of sensors, you are setting up a scenario where you could end up with a flooded yard and an empty pond.

      Is there any way to make the retro BD pull waste using siphon effect?

      That way the waterfall pump will be the only thing you need to worry about.

      Edit: Managing siphon loss will now be the thing to do. That however is much easier to do, and probably involves the use of a float switch that keeps the waterfall pump on as long as the siphon outlet is sufficiently submerged.
      Last edited by DragonFireSG; 1 Week Ago at 10:23 PM.

    3. #3
      bart is offline Member
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      Well there are bottom drains already that are gravity fed (I think) but they are only one or two inches in diameter. This is very sad news, I can imagine the whole yard flooding if something went wrong. If you're talking about a gravity fed retro bd then no, that would be very hard I think

    4. #4
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      Are the bottom of the barrels in your photo below the surface water elevation of the pond? Are the tops of those same barrels above the water surface of the pond? The retro drains, if installed correctly will gravity feed into your barrel filters. The new external pump will remove the "clean" water from the bottom of the last barrel back into your pond and/or to the top of your waterfall. Having said that, you apparently are planning a very large pond (10,000 gallons?); and the barrels you have shown in the photo will not offer enough mechanical and biological filtration for a pond of that size, plus the draw-down from barrel to barrel may be too great depending upon the pump you choose. I may have misunderstood your intended system, but if not, I don's think you will be happy with the result of your existing plan.

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    5. #5
      bart is offline Member
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      Yes the bottoms are below water level and the tops are close to the top of the water level if not above it. I believe my pond is just under 5,000 gallons. Sorry what does this sentence mean : plus the draw-down from barrel to barrel may be too great depending upon the pump you choose ?

    6. #6
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      Here are some past threads on drawdown. More can be found using the search option. Basically some pressure head is required for gravity feed any pipe. Each barrel is an open top reservoir similar to the pond. So each barrel will have a drawdown similar to that between the pond and the first barrel to push the water thru the connecting pipe. The more open top containers you have in series, the more drawdown results leading to your last container. The higher the gravity flow the more drawdown required to push the water thru the pipe. The smaller the pipe for the same flow, the more drawdown required to push the water thru the pipe. So my point; if you attempt to pump alot of water thru your series of barrels, and they are connected in series as in the following example, each barrel will add to the ultimate drawdown suffered by the last barrel. You will have less volume in each barrel than you expect.

      http://www.koiphen.com/forums/showth...stem-curve-etc

      http://www.koiphen.com/forums/showth...light=drawdown

      http://www.koiphen.com/forums/showth...light=drawdown


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    7. #7
      bart is offline Member
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      Oh cool, this is the system I believe the previous owner installed, however the pipe leading to filter 1 is very narrow. I wanted to install the retro BD instead with 3 inch pipes but it will require a second pump

    8. #8
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      Why not install a 3" drain as in the above sketch? Many retro bottom drains use 3" pipe, and are designed to be used with gravity flow.

    9. #9
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      How would the retro BD use gravity flow if it goes up hill and 13 feet? The drains could become 3" but then the pipe would still be narrow and possibly become logged with leaves, right? Plus one of the BDs is not installed correctly (it's like 4 inches too high).

    10. #10
      DragonFireSG is online now Senior Member
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      As long as the outlet of a gravity flow BD is well under the surface level of the pond, siphon effect will make it work.

      The tricky part is getting the flow started as you need to evacuate the air from the part of the drain that is above water level.

      This is achieved by installing a tee at the highest point in the pipeline, and submerged valves at both ends. With both ends closed, the pipeline is filled with water to eliminate all the air in the line via the tee. The tee is then closed, and valves on either side opened.

      Water will try to find its own level. Since the level in the filter is consistently being drawn down, there is flow in the BD.

      The important thing here is to ensure both ends - especially the one in the filter chamber - remain submerged, and are away from sources of air. Trapped air will greatly reduce flow at least, and at worst cause the siphon to fail.

      It is a good idea to install a sight glass style clear PVC pipe in the filling tee so you can inspect for air in the drain line. The fill valve should be locked or doubled up to make sure no one opens it on a whim. That on a suction line is equivalent to the self-destruct button on an evil overlordís space dreadnought. It sticks out like a sore thumb, and someday, some one will turn it just to see what happens.

      A picture is worth a thousand words. Iíll get one drawn when I am back at a PC.


      Edit pic added below
      Last edited by DragonFireSG; 1 Week Ago at 12:30 AM.

    11. #11
      DragonFireSG is online now Senior Member
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      A zakki suction sieve would be the long term solution to your filtration woes.

      If you must install a pumped BD, the interim would be to rig an overflow from the first chamber back into your pond. The overflow can exit through a filter bag to catch the floating nasties.

      You can then throttle the new pump to the point very little overflow back to the pond happens

      The risk here is that if the pump jams - which is not uncommon with a pumped bottom drain, your waterfall pump will run dry. This of course can be managed using level switch on the waterfall pump.

      ==

      That said, it sounds to me you have an obstacle between your filter chamber and the pond, which might make rigging that overflow tricky...
      Last edited by DragonFireSG; 1 Week Ago at 10:31 PM.

    12. #12
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      The thing about a 3” line is that you need sufficient flow through it to keep it clear of debris.
      If you aren’t running enough through the waterfall pump, you may not be running the drain line hard enough to keep a gravity BD clear.

      My thoughts are thus that unless you plan to increase the capacity of your waterfall/return pump as well, the pumped BD might suit you better as you can just return the excess flow into the chamber back into the pond via a coarse filter bag.

    13. #13
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      Name:  retrosiphonbd.jpg
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      I forgot to annotate in there that the maintenance valve and fill valves must never both be opened at the same time when the line is in operation.

      If the line has a problem with a lot of gas collection, the sight glass can be upsized or connected to a larger gas reservoir to increase time between maintenance operations.
      Bacteria in the pipeline naturally generate gas, so regular maintenance on a siphon line used in this setting is mandatory.
      Last edited by DragonFireSG; 1 Week Ago at 12:45 AM.

    14. #14
      DragonFireSG is online now Senior Member
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      After thinking stuff through, I think what you really need is still a Zakki sieve. Route the sieve to a couple of barrels of moving bed media, or a few DIY Birdman sand and gravel filters set up in parallel and overflow the lot to the top of your falls.

      The problem with fixing one bit in a system full of bottlenecks is that the bottleneck moves down the line immediately. A pond filter is a complete system, and has to be viewed as such. Installing the retro BD whilst retaining the old barrel settlement system will be the first step in a very long chain of other first steps.

      My worry with both a pumped BD and siphon BD is the amount of plant debris you get. This I see from your pictures. I don't think the barrels can flow enough to keep a 3" BD line clear, which is the prelude to a lot of trouble down the road.

      If a Zakki sieve is out of the question, perhaps the new BD should feed a new barrel type filter in parallel to the existing one - one set up to handle the flow rates a 3" line demands. The return need not to be the waterfall. It can simply empty over the side right back into the pond.
      Last edited by DragonFireSG; 1 Week Ago at 02:30 AM.

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