What is the minimum flow from a 4" aerated bottom drain for it to be effective in collecting waste?
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The minimum flow is 3000 on a 4" pipe, now it depends on how much your flow rate your doing by the pump and also the size of the prefilter to handle that needed flow. Don't forget the skimmer if tied into prefilter. If your pond is larger then 5000 gals then you may want to consider a second drain which would up the flow to 6000 gph. I alway use a 4" pipe in case you want to up grade then its there. Hope it helps.......................
11/2" = 350 gph
2" = 750 gph
3" = 1500 gph
4" = 3000 gph
Koiman™
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Max Flow?
Are we talking gravity flow or direct suction? I am assuming most all (99.9%) of the applications here will be GRAVITY FLOW. I just want to clarify the question.
The question as I see it is, MINIMUM flow rate in an aerated 4" bottom drain. I suppose it is relative to what you are flowing into, yes or no?
It is my understanding that the MAXIMUM flow rate into a 4" gravity flow bottom drain is 3600 GPH and a 3" bottom drain is 1800 GPH.
So the original question. What is the MINIMUM recommended flow rate for an aerated 4" bottom drain?
If I may, add to the topic 
What is the OPTIMUM flow rate into a 4" aerated bottom drain?
For example, what I have soaked up is  The Large Nexus filter is designed for a 4" feed and in doing so, puts a MAXIUM SPEED LIMIT on that filter of 3600 GPH. I have not read the manual personally but have talked with several different sources regarding the performance of the filter. So in regards to the large NEXUS filter; What is the OPTIMAL flow rate recommended on a 4" gravity flow BD? Aerated or not?
And Can we confirm  What is the MAXIMUM recommended flow rate for an aerated 4" gravity flow?
Does the MINIMUM, OPTIMUM & MAXIMUM flow rate change when their is an air dome on the BD or does the air dome just optimize the sweeping of debris off the bottom of the pond into those flow rates?
I hope this is not one of those questions that varies widely depending on whom you are talking. Cold hard numbers PLEASE...............
Respectfully,
The Pond Digger"Doubt sees the obstacles, Faith sees the way!"
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My pond will be a 9x14x5 oval with a capacity of about 4,000 gallons. Can a 3" bottom drain adequately remove the debris from the bottom of such a pond? If so, assuming 1,500gph from the BD, can enough additional circulation be obtained through a skimmer (perhaps 1,000gph or 1,500gph) to have a healthy pond? At 1,000gph through the skimmer the turnover time would be a little less than 2 hours; at 1,500gph through the skimmer the turnover time would be about 1 hour and 20 minutes.
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hello Gary i new wih hobby but i can tell you 3' pipe not enough it only carry 1800 gpm you need 5000 to 6000gpm due to 4000gl pond you have. it will be 1 bottom drain 4' about 3600 gpm and 2 skimmer 2' about 900gpm or one midwater 3' about 1800gpm. i know it because i will have a pond like your pond
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Sweeping.......
It is my understanding that a 3" bottom drain is effective at sweeping a 6' to 8' diameter and pushing the limits to a 10' diameter, depending on who you talk to. Of course, if you are going to push to the limits, an air dome is highly recommended for effective sweeping. Where as a 4" BD would effectively sweep a 10' to 12' diameter for optimal sweeping and a 14' diameter would be pushing the limits.
Now mind you, we are assuming the bottom of the pond should always be bowled down to the lowest depth of the pond where the BD would be installed for the most effective sweeping of debris for removal from the pond.
I suppose this information is all subjective depending on what the MINIMUM, OPTIMUM & MAXIMUM flow rates are being used, what you are flowing into, how heavy your fish load is, how much leaf debris you pond is subjected too, if you are raising male or female koi, and again of course who you are talking to.
But what do I know? Look what happens if I stay up to late on the computer
With All Due Respect,
The Pond Digger
P.S.
I'll go pick out a switch.............."Doubt sees the obstacles, Faith sees the way!"
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as I posted on Koishack...
You can dimension BDs two ways: by gallons served or by area of floor space served.
Gallons served.
The shape of the curves in half of the oval make a huge different in the gallons the pond contains. When I calculate 9x7 (half of the oval) x 67% (the volume inside a sine wave) x 5 x 7.48 (gallons per cubiic foot, I get 1578.654 gallos. So the total volume would be a little over 3200 gallons. But that all depends on the shape of the oval's curve. The closer it is to a rectagle....the larger the volume inside the curve. You know the shape so indeed lets assume each half has 2000 gallons and the total is 4000 gallons.
Typically a koi pond system is designed to turn over the water through the filters in ~1 hour. The larger the pond...the more this target sildes towards 2 or even 3 hours do to the increasing costs of more BDs, filters, and pumps. So from a gallons servered perspective, using a 4" BD gravity feeding one fitler system....this pond could be served by one BD/filter/pump combo doing 30003500gph. And tha does not take into consider any water going through a skimmer to a pump (through some type of filter?) and back to the pond. Such a system should be just fine.
Floor space served
A BD can help gather sinking debris/mulm from the pond floor. The antivortex cover over the BD keeps the "suction" aimed parallel to the pond floor. That suction is strongest at the BD and disapates as you get further from the BD. So folks willl plan a BD doing ~3000gph to service floor area in a max radius of 68'. So if we put one BD in the middle of a 9x14 oval, the width of 9' is probaly served well enough. The problem may be in the 14' length. You may tend to get settlement in the ends of the oval.e. One way to address that would be to put TPRs at each end of the 14' length to help prevent any settlement. Another choice would be to put a BD in each logical half of the oval. If the BDs were 4" the flow for each should be ~3000gph to prevent settlement in the pipe. If the BDs and pipe were 3" the flow on could be ~2000gph. Don't forget to use BDs with air domes in either case!!!
Bottom line....from a gallons served perspective, one 4" BD feeding filters should be just fine...especially if the skimmer circuit also has filtration. From a floor space perspective you could get by with one 4" BD and pipe if you carefully place TPRs to prevent settlement in the ends of the oval. Another choice would be a 3" BD in each half of the oval.Koi keeping is not a belief system; it is applied science with a touch of artistry.
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For example, what I have soaked up is  The Large Nexus filter is designed for a 4" feed and in doing so, puts a MAXIUM SPEED LIMIT on that filter of 3600 GPH. I have not read the manual personally but have talked with several different sources regarding the performance of the filter. So in regards to the large NEXUS filter; What is the OPTIMAL flow rate recommended on a 4" gravity flow BD? Aerated or not?
Nexus Eazy 300
Max flow rate: 15,000 litres/hr 3,300 UK or 3,900 US gallons/h
This is what the Mfg. has in pdf instruction book, so based on that fact we need to know what really is true flow rate. From field experiance I will take an educted guess of 31003400 gph.
Faster and higher flows are not always the best option
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Koiman™
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Optimal Flow Rates...........
Let us mention that faster and higher flows being, or not being, the best option could also depend on what you are flowing too.
Strictly speaking of Bottom Drain Circuits, understand that if you are flowing into a settlement tank, a slower flow rate would be more optimal than faster flow rates, to increase the dwell time in the settlement chamber thus allowing solids to settle out.
However, if you are running your BD into a sieve, like the CETUS, then dwell time is really not of concern. Of course, this is all based on ponds with normal stocking rates, feeding regimen, optimal temperature considering frost lines, etc., and so on. I am sure we will have fans of sieves on BD circuits and then we will have polar opposites.
So many variables is the construction of traditional koi ponds.
http://www.koibito.com/forum/koigr...outstats.html
Respectfully,
The Pond Digger"Doubt sees the obstacles, Faith sees the way!"
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