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    Thread: DIY RDF "2.0", The Beast

    1. #1
      kimini is online now Senior Member
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      RDF "v2.0", The Beast

      First off, I want to give full credit to Zoki51 for his generosity in presenting his DIY RDF project which formed the basis of this one. My project here isn’t anything new but it’s my take on fabricating an RDF from raw materials. This thread will be something of a blog/diary so no doubt you'll see a few goofs. The goal is to end up with a kick-butt RDF that’s utterly reliable, built to last decades, and is easy to maintain. That said, I’m not sure how useful the design will be to others because it involves fabrication using various tools and techniques that some may not want to pursue.

      Background:
      The previous RDF was based on Zoki51's design, but me being me, I strayed from his proven design in a few places. He used a straight-sided drum but not realizing that, I used a more ordinary drum with its typical “fat waist”, where the middle of the drum has a larger OD than the top and bottom. The problem comes when a sheet of filter material is wrapped around it, it causes all sorts of issues with folds or stretching*. Also, the drum wasn’t truly round, wasn’t square, and the wall thickness varied tremendously. There were other things about my implementation that I wanted to improve upon. The IBC container is very flimsy, fine for its intended use, but not so much for an RDF. The steel frame of the IBC is lightly galvanized so will start rusting in its watery environment. It wasn’t easy to ensure a liquid-tight seal to keep dirty water from going around the drum due to the IBC wall flexing. Then there was the sliding seal from the bulkhead to the drum. I “think” it’s working now but it could probably be improved upon – just as soon as I figure out how. The sprayer uses tap water at approximately 60 psi and is very loud, not great in an otherwise-serene pond setting.

      RDF v2.0, The Beast
      Many store-bought RDFs (in the US at least) tend to be manufactured overseas, are very expensive, and may use proprietary parts. The goal (and challenge) of RDF v2.0 is beat their reliability, flow rate, and cost:
      1. High reliability
      2. Uses easy-to-source parts
      3. Easy maintenance
      4. High flow capacity
      5. Quiet
      5. Competitively priced

      Design decisions:

      Drum “wrap”:
      The design centers around using what’s commonly available. The key elements are the support covering the filter element and the filter material itself. The decision was made to base the design around a standard-size 48” x 96” sheet of thin expanded and flattened 316 stainless, which is cheaper than metal woven cloth of the same size. This size sheet results in a 30.5” diameter by 48” wide drum, which will have roughly double the flow capacity of my current plastic drum unit and giving huge flow capacity. “Cheap” is relative though, at $300, it’s a reminder that this isn’t a toy.

      Filter element:
      I chose to go with filter cloth again instead of stainless wire mesh. The availability of stainless mesh is a bit of a hodgepodge. That is, there seems to be no standard sizes, sometimes it’s 36” wide, sometimes 48”, and sometimes 54”. Available lengths is even more annoying, where “standard” can be 36”, 48”, or “by the foot” – with a catch. “By the foot” implies you can buy it, you know, by the foot, but they only sell it in strange increments. Want 8 feet of the stuff? You have to buy – and throw away - two feet, and around $70 a foot, it’s very wasteful. Polyester filter cloth on the other hand comes on a roll, so having spare material on-hand is not an issue and you obvious just cut off what you need, makes replacement faster and involves less bleeding when compared to stainless!

      [Edit] I changed my mind later, as the polyester filter cloth kept tearing prematurely in the previous build.

      Enclosure Material:
      What to make the unit from came down to stainless or plastic. While I could have fabricated it from 316 stainless, it’s not fun to work with, makes me bleed, and is really hard on cutters. It also guarantees that practically no one would build this unit, so attention turned to plastics, specifically High Density polyethylene ("HDPE") or polypropylene ("PP"). Which is better depends who is asked though; plastics shops recommended PE, saying it's easier to fabrication, but others said that PP machines better. A variation is something called “HPDE Seaboard”, basically HDPE with additives to make it last in the sun. It comes at a price premium though and due to the additives, may or may not work with regular welding rod…

      Yes, welding rod. It turns out that there’s an entire industry that uses plastic welding to fabricate liquid tanks, display cases, and jigs. A plastic welder is sort of like a cross between a hair dryer and a soldering iron and is used very much the same way as when welding metal. Having to buy and use a plastic welder may dissuade some people from pursuing this project, but it’ll at least demonstrate one way of building such a unit, and it’s a chance to learn something new!

      Cutting Plastics:
      Various methods are used much like when working with wood: a table saw, band saw, CNC router, and water jet. Special cutters are used along with a workflow that minimizes the material melting and sticking to the cutter. The slick way for a home builder to make this RDF is to get everything cut via CNC router or water jet cutter, then assemble it like a kit - unfortunately the problem is cost, but let me back up for a second to explain.

      The design needs to address the following conditions: In operation, dirty water flows into the drum, then flows through the filter element and out the bottom. Over time, the filter plugs up and the outgoing water level drops, leaving the drum “holding the bag” so to speak. If the outgoing water level is, for example, 3” lower than the water inside the drum, then the drum is supporting approximately 65 lbs over 19” of its face. That force is directly supported by the filter element, so it has to be well supported to not tear, sag, or pull away from the drum and allow water to bypass the filter material. This is what the sheet of expanded and flattened 316 sheet does, used as a wrap-around collar for the entire drum and fully supporting the filter element. But we aren’t done yet…

      When the output-side water level drops, the drum rotates the dirty portion of the filter up to the sprayer and it does its thing. While there is very little actual force against the filter material, it is still being pushed toward the interior of the drum and for the same reasons above it must be supported. Given that we have a clean sheet of paper, I chose to fabricate everything, including the drum, because nothing could be found in that size which was both the right material and perforated (I did find a perforated designer stainless trash can - $800, nope). Fabricating an RDF from scratch is a bit of a double-edged sword. It gives you complete design freedom, but also allows you to do things really wrong since there are no limits.

      I decided to fabricate the wall of the drum using plastic ribs. Individually they aren’t very strong, but placing one every inch results in a very stiff yet light assembly (somewhat like an old wooden aircraft fuselage). The downside is cutting costs, quoted at $180-200 per disc. Given that there’d be three slotted bulkheads (top, bottom, and middle) and possibly two smaller supports mid-span, the entire project ended up with a total cutting charge of $1000-1200, not counting material! That was a no-go.

      Change of plan
      This seems like the perfect time to buy a router, something I’d always wanted but never had an excuse to get. Mounted to a temporary table, fixtures could be made to handle cutting both the slots as well as the large circular sections.

      More to come...

      *I used polyester filter cloth which is supposedly more resistant to plugging and is WAY cheaper. One issue is that it gets pulled one way when it’s supporting the weight of the water, and gets blown the other way with the sprayer. It’s unknown how long it’ll last getting pushed back and forth. What remains to be seen though, regardless of material used, is if bio growth on the screen will plug it up. It might… and might not. The chlorine in the tap water “may” prevent bio film build up, but we’ll see. Curious what other RDF users have found.
      Last edited by kimini; 04-11-2017 at 04:42 PM.

    2. #2
      kimini is online now Senior Member
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      Initial test welds on scrap 0.50" HPDE were amazingly strong.
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    3. #3
      Jaymeseywaymsey's Avatar
      Jaymeseywaymsey is offline Senior Member ~~ Facebook Content Editor
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      PM me... I own a CNC Router that has a 1 meter cutting bed, and I've been working on a DIY drum filter myself. A meeting of the minds perhaps.

      James.

    4. #4
      kimini is online now Senior Member
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      PM sent

    5. #5
      kimini is online now Senior Member
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      Router has arrived, accessories on the way.

    6. #6
      kimini is online now Senior Member
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      During the thinking stage of this, I saw an RDF that uses water pressure to drive drum rotation and valve actuation. I thought that was very clever since it would continue to operate even without electricity - pretty cool. The more I though about it however, the feature seemed less clever in terms of actual usefulness. First, not needing electricity is a moot point since presumably if the power goes off, so does the main pond pump. I saw arguments arguing that not needing electricity equates to being more reliable. If anything, I think it would be the opposite; with electricity, there's a motor, solenoid, and controller. With an all-mechanical solution, there's a cylinder, pistons, rods, linkages, valves, seals, floats, and springs. So the unit will operate as does the interim model being used now, using electrical power to rotate the drum and controller, and city water pressure poweringr the spray bar.
      Last edited by kimini; 07-05-2017 at 05:17 PM.

    7. #7
      kimini is online now Senior Member
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      The 316 sheet arrived. First thing was to form it into a rough cylinder, not just to confirm measurements, but also to make it smaller by either disposing of its enormous shipping envelope or cutting it up for future pattern material. The round cardboard tube on the yellow saw horses was used to form the cylinder.

      Surprisingly, the ends of the sheet weren't the same length. This was especially odd because both the upper and lower cuts aligned with the diamond pattern, but life is too short to worry about it so it was trimmed, which made me bleed a few times. Still to do is cutting the resulting cylinder vertically and forming two 180-degree sections, with a piano hinge connecting them. This way it can be removed from the finished drum filter assembly without having to remove the drum first. Once the cuts are cleaned up, final drum diameter can be can be established, but it should be really close to 30.5" (8'/pi). The reason the screen was dealt with first is because typically, when a 48" x 96" panel is ordered, it's never exactly that! If it's undersized the drum will be designed to accommodate that. The screen will be latched into position with over-center latches, unless the ends insist on springing up away from the drum. If it won't lay flat, giant 31-inch diameter(!) hose clamps should do the job!
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      Last edited by kimini; 02-07-2017 at 05:05 PM.

    8. #8
      rayrod2030 is offline Senior Member
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      This is going to be amazing! Can't wait for more updates.

    9. #9
      kimini is online now Senior Member
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      Below are expenses and sources. Some listed prices include shipping when it makes a difference. I chose to leave out tool expense since presumably they're useful for other things and you may already have them. Most stuff below is from McMaster.com* and exceptions are noted.

      Drum assembly:
      $360 4' x 8' 0.040" expanded and flattened 316 stainless.
      $18 4' 316 piano hinge
      $24 Draw latch, Qty 3
      $90 50-yards 65-micron Rayon/Polyester Filter Fabric, 0.008" Thick (roll length should last a lifetime)

      Controller, power supply, motor, and gears:
      $160 150-tooth stainless #35 chain sprocket - custom made by local water jet shop
      $12 Nylon Machinable-Bore Sprocket, ANSI #35 Roller Chain, 3/8" Pitch, 9 Teeth
      $70 Plastic Roller Chain, Acetal, ANSI Number 35, 3/8" Pitch, 7 feet
      $83 Makermotor Electric Gear Motor 12v 50 RPM, 8.5 ft-lbs, Amazon
      $33 Meanwell 150w 12V 120 to 12 Volt DC Output Switching Power Supply, Amazon
      $20 10A Mini Timer Time Delay Relay 12V, Amazon

      Plastic, HPDE
      $750 54" x 96" 0.50" thick Seaboard, tan, eplastics.com (load-bearing outside housing) - 3 sheets
      $120 54" x 96" 0.25" thick Seaboard, tan, eplastics.com (inner panels, non-load-bearing) - 1 sheet
      $120 54" x 96" 0.25" thick Seaboard, black, eplastics.com (inner panels, non-load-bearing) - 1 sheet
      $48 48" x 96" 0.125" thick, plain HPDE, eplastics.com (drum ribs) - one sheet

      ===============
      This totals to about $2000 not counting a few "bits and bobs" as the Brits say. It's a lot, but compared to what? It's a lot less than the currently-popular $6000 unit and has much higher flow capacity. Yeah I could have bought a used one but like I said, I greatly enjoy building stuff, so no complaints.


      *I use McMaster for a lot of stuff because they're convenient and have nearly everything, but it's a love/hate relationship. The annoying downside with them is that they have very high shipping charges. It very much depends what you buy and how much, plus they take the lazy and profitable way out by choosing from an apparently limited selection of shipping containers. For example, if you buy a 12" x 12" x 1/16 panel of something, it'll be shipped in a 12" x 12" x 12" box, with you sucking up the charge for shipping a cubic foot of air. They have no concept of shipping anything inside an envelope. Another situation is buying something long, which they drop into a heavy-duty cardboard tube. Buy a 1" x 48" piece of plastic for $4? Expect to pay $26 for shipping. Just saying, weigh their convenience and stated price against their actual shipped price - which they cleverly hide until after it's shipped. Sometimes I put in the "special instructions" section to ship certain items together - they often ignore that and make me pay an extra $20 on shipping... like I said, love/hate. If you can find something local I recommend getting it there instead, but often they're the only game in town, and they know it.
      Last edited by kimini; 02-22-2017 at 02:34 PM.

    10. #10
      kimini is online now Senior Member
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      The drum filter will be made from HPDE, but there's an HPDE variant named SeaBoard that's UV-resistant. It's about 20% more expensive and leads to the question: will this unit be sitting in the sun and is UV-resistance needed? The answer is "not really" but also not "no." Short term it will be in the sun - unless I throw a tarp over it - until I make a shelter for it and all the other filter-related bits and bobs. To ensure a long life, it'll use Seaboard "just to be sure."

      Also, most of the material will be black. This is both to cut down on the chances for algae buildup on the inside walls, and to keep stains or other water-based marks hidden from view from the outside.
      Last edited by kimini; 02-08-2017 at 05:28 PM.

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      kimini is online now Senior Member
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      Yeah the irony will be if it reaches the point where a used "real" RDF could be purchased. Me being hard-headed though, I'd build one regardless.

    12. #12
      kimini is online now Senior Member
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      The truth is that I just like building stuff.

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      This going to be a great thread along with Zoran's...

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      kimini is online now Senior Member
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      Received the stainless gear, it'll do I did the math and realized that the all-plastic chain will break if the drum needs more than 30 ft-lbs (45 ft-lbs for stainless) to turn, but it shouldn't be an issue since the drum will be on four rollers. With this gearing, the drum will make one full turn in 20 seconds, so figure a 10-second spray time for half a rotation. The slow speed will ensure a good cleaning by the spray bar.

      Made up a temporary router table to cut the 96 ribs and learned about the nature of using a router to cut plastic - having the right cutter helps a lot.

      The last picture was just something I took while walking the dog this morning. The combination of back-lit trees and fog came out really nice.
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      Last edited by kimini; 02-11-2017 at 12:16 AM.

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      Can't wait to see the progress.


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      vipertom1970 is online now Senior Member
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      Quote Originally Posted by kimini View Post
      During the thinking stage of this, I saw an RDF that uses water pressure to drive drum rotation and valve actuation. I thought that was very clever since it would continue to operate even without electricity - pretty cool. The more I though about it however, the feature seemed less clever in terms of actual usefulness. First, not needing electricity is a moot point since presumably if the power goes off, so does the main pond pump. I saw arguments arguing that not needing electricity equates to being more reliable. If anything, I think it would be the opposite; with electricity, there's a motor, chain, water solenoid, and controller. With an all-mechanical solution, there's a cylinder, pistons, rods, linkages, valves, seals, floats, and springs. So the unit will operate as does the interim model being used now, using electrical power to rotate the drum and controller, and city water pressure poweringr the spray bar.
      Glad to see another smart person sees it this way. The irony is this person talks about how electronics is not reliable but also promoting BE pumps with an electronic controller ......... BTW, cool build.
      Last edited by vipertom1970; 02-11-2017 at 03:22 PM.

    17. #17
      Riftlake is offline Senior Member
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      Sprockets and chain are expensive. I wonder if pulleys and belt would work. The biggest aluminum vbelt pulley I saw on Ebay was 14" though. Maybe could scrounge up something used that would work off an old furnace blower or evap. cooler.

    18. #18
      kimini is online now Senior Member
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      I thought of that, like a cogged stepper motor rubber belt and sprockets, but the same problem seemed to be there as well, that an enormous sprocket would be needed and I didn't find any. Also, what sprockets are out there for stepper motors all seem to be aluminum. Several alternatives come to mind:

      1. Machine the sprocket pattern directly into the drum end plate. The sprocket would thus be made of HPDE, but shouldn't be a problem with so many teeth carrying the torque. The machining costs for this were more than just having the stainless sprocket made.

      2. Get rid of the chain and drive the drum gear directly with a spur gear off the gear motor.

      3. Drive the drum directly through the outside wall with a proper gear motor.

      4. Use a friction drive, extending a shaft through the end of the filter housing and having it ride on the drum end plate. It would probably have to be spring-loaded to ensure enough traction, but would be way cheaper. It also allows a nearly infinite gear ratio selection. I didn't go this way because I didn't want to deal with development time in case slipping became an issue when I'm away.
      Last edited by kimini; 02-12-2017 at 12:02 AM.

    19. #19
      kimini is online now Senior Member
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      The rest of the 96 ribs were cut and finished, at right. The rejects are under the table, kept around in case they're needed for something else.

      Next was cutting the drum frames, starting with the basic discs:
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      I call this picture "Using tools to make tools to make parts to make a filter". Making a router fixture to cut the rib notches in the frames.
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      Then the centers were cut out:
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      Leaving rings:
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      This gives a rough idea of how it assembles. I was just screwing around here and not worrying about alignment. The nice thing is that the ribs are a really tight fit in the slots such that the entire affair is self-jigging. When the first 8 ribs were installed, the assembly was really "floppy". Adding the next 8 helped a lot, and with all 96 it may be stiff enough to not need diagonal bracing, but we'll see. I already have a solution in mind in case that's needed, really simple and inexpensive.
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      Here the bits are being placed to construct the assembly. All ribs will be installed before being plastic welded:
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      Last edited by kimini; 02-13-2017 at 02:14 AM.

    20. #20
      Marlo is offline Senior Member
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      Awesome project! Thanks for sharing.

      There was a time not so long ago when I would have been tempted to take on a design/build like this. But frankly, every time you post an update I feel better and better about my decision to pop for the ProfiDrum!
      63m3 gunite pool
      ProfiDrum CombiBio 50


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