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  • Page 3 of 3 FirstFirst 123
    Results 41 to 54 of 54

    Thread: RDF filter mesh flow rate/pressure drop

    1. #41
      kwickcut's Avatar
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      Quote Originally Posted by ZephTheChef View Post
      That's probably the most directly helpful response so far. That gives me pretty much all of the exact and specific data I was looking for on a finer screen. Do you have a link to the exact screen you are using, or do you know if that micron rating is nominal or absolute? It can be confusing and make no sense how some manufacturers rate them. Like the "43 micron" screen I was looking at is actually more like 30-something micron absolute and 25 micron nominal. I assume the 43 micron is the actual opening size, but because of how the weave is set up it's actually finer filtration than that. In other words, it would be useful to know exactly how your screen compares to that screen.

      So let me clarify your setup before I do all the math. Did you mean 4" of draw and 9" of draw, or did you mean 1" and 6" (less your 3" drum height)? In other words, you have 8,000gph through an 18x24" drum @ 38 micron, which clean has 15" of static submergence and 4" of draw and dirty is 9". OR did you mean the clean water starts out 4" below the top of the drum, which would be 1" of draw based on your dirty level being 3" below the top? Attachment 579214
      left drawling

      this is the only specs i could see in my pdf the screen i am using is 50x250
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    2. #42
      ZephTheChef is offline Senior Member
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      Quote Originally Posted by kimini View Post
      The screen I linked to was for the physical properties only. Yes, my drum is ~30" diameter and 41" across. Overall, my goal is to use the most open screen I can and not notice stuff floating in the water. To me, there's no reason to filter out such small stuff that I can't even see it, and it drives up cost and needless cycling of the drum. In a few weeks or months I'll know if I've gone too far in increased wire spacing.
      If I had a larger pond that would probably be my goal as well. For flowing a couple thousand gallons an hour, and considering small quantities of screen compared to what I bought wouldn't really have saved any significant money I just went with the 48x72 screen @ 50 micron which I felt was aggressively fine, but probably ok at my flow rate. I think the 33 micron would be pushing it even in my case with a 2,000gph flow rate with a drum which is something like a 25,000gph capacity based on what the sizing is compared to what manufactured ones advertise. I know that at some point the flow just drops to a trickle without significant feed pressure, but I don't know exactly what pore size that is. I suspect it's in the 20-30 micron range where things simply become impossible at any reasonable flow rate with gravity, but I know that 50 is already going to be a heck of a lot slower than 100. You may well be on to something, though...I'm probably chasing invisible results.

    3. #43
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      Quote Originally Posted by kwickcut View Post
      left drawling

      this is the only specs i could see in my pdf the screen i am using is 50x250
      Cool, thanks for that!

    4. #44
      kimini is offline Senior Member
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      Quote Originally Posted by ZephTheChef View Post
      If I had a larger pond that would probably be my goal as well. For flowing a couple thousand gallons an hour, and considering small quantities of screen compared to what I bought wouldn't really have saved any significant money I just went with the 48x72 screen @ 50 micron which I felt was aggressively fine, but probably ok at my flow rate. I think the 33 micron would be pushing it even in my case with a 2,000gph flow rate with a drum which is something like a 25,000gph capacity based on what the sizing is compared to what manufactured ones advertise. I know that at some point the flow just drops to a trickle without significant feed pressure, but I don't know exactly what pore size that is. I suspect it's in the 20-30 micron range where things simply become impossible at any reasonable flow rate with gravity, but I know that 50 is already going to be a heck of a lot slower than 100. You may well be on to something, though...I'm probably chasing invisible results.
      The issue is that the flows listed are for clean water. Add debris and biofilm growing on the wires, and the flow results will be "less" by some mystery amount.

    5. #45
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      Yeah, and the finer the screen the faster the flow rate drop will happen. I have a lot of experience with bulk water treatment and filtration, just not as much in gravity-fed systems so trying to compare the surface areas required is impossible when information on most filtration, even the "free flow" low pressure drop ratings are going to be equivalent to if we had like 20 ft of gravity pressure, lol.

    6. #46
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      I have three name brands of Rdf's that run 24/365 I use air lifts also and combinding an airlift and Rdf and work reliably
      NASA may be able to help you out.
      First of all the screens will lose flow with bio load
      Bio load in the airlift loses flow in time
      There can be no draw down in the drum
      Of the many that I've seen in operation have upwards of 2" of draw down
      I have 2 Rdf's with 1/2 " drawdown
      12" plumbing with no turns and short runs
      I build a lot of diy projects this one I wouldn't touch with a ten foot pole

    7. #47
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      Experiment with the size of the screens openings till they match the biomass load adhesion size?

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    8. #48
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      Quote Originally Posted by tsippel View Post
      I have three name brands of Rdf's that run 24/365 I use air lifts also and combinding an airlift and Rdf and work reliably
      NASA may be able to help you out.
      First of all the screens will lose flow with bio load
      Bio load in the airlift loses flow in time
      There can be no draw down in the drum
      Of the many that I've seen in operation have upwards of 2" of draw down
      I have 2 Rdf's with 1/2 " drawdown
      12" plumbing with no turns and short runs
      I build a lot of diy projects this one I wouldn't touch with a ten foot pole
      That's the range of draw I was thinking I would like to target for use with airlift. I'm not sure if I'll hit that target or not but sure gonna give it a shot. Do you have info on your drum sizes, what micron, and what flow rate? 12" piping is...wow! 10x the flow area of 4". That's impressively overkill if you're flowing short of about 200,000GPH. I understand how important pressure drop is with air lift though...and it's not just the flow area, but the volume to surface area ratio gets a lot better with bigger piping too which also reduces friction.

      I will not be allowing bio to establish (in this circuit), I have other plans for that. The RDF loop will remain basically sterile via ozone, UV, and tap (chlorinated) rinse water, as well as periodic systemic potassium permanganate treatment followed by hydrogen peroxide.

    9. #49
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      Quote Originally Posted by ZephTheChef View Post
      That's the range of draw I was thinking I would like to target for use with airlift. I'm not sure if I'll hit that target or not but sure gonna give it a shot. Do you have info on your drum sizes, what micron, and what flow rate? 12" piping is...wow! 10x the flow area of 4". That's impressively overkill if you're flowing short of about 200,000GPH. I understand how important pressure drop is with air lift though...and it's not just the flow area, but the volume to surface area ratio gets a lot better with bigger piping too which also reduces friction.

      I will not be allowing bio to establish (in this circuit), I have other plans for that. The RDF loop will remain basically sterile via ozone, UV, and tap (chlorinated) rinse water, as well as periodic systemic potassium permanganate treatment followed by hydrogen peroxide.
      I'll be interested to see if you can do it. Seems nature will be fighting you all the way.
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    10. #50
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      Quote Originally Posted by icu2 View Post
      I'll be interested to see if you can do it. Seems nature will be fighting you all the way.
      Well if I know one thing, it's that nature is just a system striving to be in balance. Biofilm is a response to contaminants that the bacteria can use as an energy source. Remove the contaminants and the bacteria can't multiply. Particularly if your entire water volume is being sanitized every half hour or so.

      I'm actually now contemplating using pond water instead of tap for the RDF cleaning...and having the waste drain to an isolated biofilter tank where the bacteria would be more than welcome to come hang out, such that I will have a colony ready to go for emergency purposes if one or more of my other systems fails to do the job. Redundancy is important when there are lives at stake.

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    11. #51
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      any updates?
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    12. #52
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      Smaller micron means slower flow. Plug in a flow meter to use 50 micron and see what the output is. If you do a smaller diy micron make sure the drums sieve itself is bigger because it’ll clog faster compensate for the less flow from the 50 sieve micron restriction

    13. #53
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      Wire mesh:

      Micron hole size
      Wire diameter
      Percent open area

      All determine flow rates and size of capture. Smaller wire diameter allows a higher percentage of open area and higher flow rate for a given micron size. The RDF drums open percentage area exposed directly to the screen will also impact flow rates.
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    14. #54
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      For example McMaster Carr stainless mesh 74 micron hole size. One has 46% open area and greater flow vs 34%. The smaller diameter wire the easier to damage.
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