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  1. #16
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    Quote Originally Posted by auscab View Post
    Thanks Pete , Thats very interesting!
    The vacuum inside the system is the magic ? Amazing .
    So if a fan in a system was spinning but not hard enough to create as big a vacuum , shavings could just fly in and out the exhaust ?
    Not drop down?
    I'm going to go read on how the storm type of Cyclone works as soon as I get the time.

    Rob
    The vacuum is part of how a cyclone works, another way to visualize it is that the fan creates an empty space by pushing air out the exhaust, the air that is outside the system tries to rush in to fill the empty space that is inside the system.

    If there is high resistance to flow (small dia pipe, long length of pipe, lots of fittings, long flex hose, etc) the air can't get in as fast as it wants to so this gives us a high vacuum number, with the system inlet fully blocked (the spade) this gives us max vac but no air flow, the opposite is fully open which gives us max flow and a low vac number, to take Bob's value of 10" and lets say that was measured at the fan inlet but we then took another reading at the cyclone inlet it might read 8.5", What happened to the 2.5"? It is "consumed" by the internal resistance of the cyclone.

    Each metre of pipe/hose, type of fitting, all have a value of loss (back pressure) the more stuff we hook up increases the back pressure and if you hooked enough stuff or did something like put on a bit of 32mm dia hose, the original 10" is all consumed and you get very little flow, (the spade), so if there is minimum flow there is minimum air speed inside the cyclone and little centrifugal force so particles are not held out against the cyclone wall and remain entrained in the airstream and out the exhaust they go, if the air speed is high enough the particles are separated from the air stream (centrifugal force) and held out on the cyclone wall, friction and gravity do their thing and into the bin they go.

    Pete

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  3. #17
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    I believe the 10" Bob was talking about in his reply was static pressure ie. system blocked. In that case the the 10" should be the same at the fan inlet or at the cyclone inlet unless there is an air leak. You will only get the drop through a cyclone if there is air flowing.

  4. #18
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    Well yes, I was just taking 10" of WC as a number, Auscab could well have 10" of WC with air flowing, the main point of my reply was to try to expand a little on why and how "back pressure" occours.
    Pete.

  5. #19
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    I just wanted to point that out as I didn't want Auscab's hopes to get up as 10" velocity pressure on his system equates to approx 4400 CFM

  6. #20
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    Quote Originally Posted by Lappa View Post
    I just wanted to point that out as I didn't want Auscab's hopes to get up as 10" velocity pressure on his system equates to approx 4400 CFM

    You guys are not getting my hopes up cause some of this talk is over my head . I'm interested but don't want to get to far into it . I did that last time. And did it with Vacuum pressing veneers. And the stars . And all the rest . And then I forgot it all .Well most of it . Just as long as the dust ends up in the bin and that will do. And I don't get ripped off buying pipes .
    Man The suppliers know how to charge for the big size PVC! I have a plumber mate who will get me some at trade price thank goodness. That sort of mark up from trade to public is BS.

    Rob

  7. #21
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    Looking at that beast you have Auscab, I don't think you'll have any problems with flow. Know what you mean about plumbing prices. The worst near me are Reece - I queried a price on some items and they said if I had an account I'd get it cheaper. So I said - right oh, open an account for me. Their reoly - can't do, you don't buy enough!
    I've found Trade Link better for prices but still no where near as cheap as pipeonline in Perth.

  8. #22
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    For a large order it might be worth getting a shipping quote from pipeonline.

  9. #23
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    I've spoken to them on this subject. Their more than happy to satchel over smaller items and that certainly is worth it, but freight on larger items such as pipe is a killer. When I was looking for 125mm pressure pipe, their price plus freight equalled what I could buy it from here but that shows how good their prices are.

  10. #24
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    Quote Originally Posted by Lappa View Post
    Know what you mean about plumbing prices. The worst near me are Reece -

    I've found Trade Link better for prices but still no where near as cheap as pipeonline in Perth

    .
    Reece were my first try , so things can only get better .
    Price was still cheap from Pipeonline for you even though they are in WA and you are in NSW?

    Edit . My Plumber Mate is using Trade link . Massive difference from the price from Reece.
    For a 6 M length roughly $280 down to $155

    Rob

  11. #25
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    Quote Originally Posted by BobL View Post
    For a large order it might be worth getting a shipping quote from pipeonline.
    Ill give it a try .

  12. #26
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    Rob, I didn't buy from them I just drooled over the prices on their website . See my earlier post. They were happy to satchel small items but I never got a total price (including freight) on Elbows or junctions, which are the costliest items. I may be wrong, but I got the feeling that they supply some distributors over on the eastern seaboard so weren't real fussed on sending pipe. The prices I got on freight for two lengths of 125mm pressure pipe brought the pipe to a similar price as what I could buy it here for.

  13. #27
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    Hi Guys . Back with another question .

    First . Ive finally got things organized and moved tonnes of stuff around to get excess machinery out of the way to an outside hay shed storage area. Arranged the remaining machines into their working places and I'm ready to buy pipe to connect the beast up . Since this thread was started the Cyclone unit was installed outside on a slab and wired up so its running and under its own small roof . I did a thread on that in the vintage machinery section if you want a look . The Dusty

    So now that I'm ready to buy 225 PVC for the main pipe connection to my 200 mm inlet on the cyclone and 225 / 150 branches to go off in different directions an option has come up which seems to good to pass up .

    A factory worth of similar size machines to me with metal Gal main line at 300mm and 150mm and 100mm branches joining into it has become available to me .

    15 meters of 300 mm and 50 meters of 100 and 150 with enough branches for all my machines and floor dust sweep gates . Some larger duct as well . And its cheap! Compared to the PVC I may have to buy anyway. $750 in steel compared to at least $2500 in PVC for starters .
    I do have to go pick it up, 2.5 hours away and take it all down though . Which is fine .

    The questions .
    If I connect 300 mm main line up to this cyclone I'm going to have to cut the inlet back to open it up . Yes ?
    The inlet is currently 200mm at the Green arrow and if I cut and shape some 300 to fit around the more rectangular section back where I circled in Green and Red the circumference their is roughly 880 mm so an area roughly off 616 cm2 . I may be able to get a few cm back from that even ? For a little more CM2.
    Edit . just realized Its probably not worth it because of the limiting exit CM2 Yeah ?

    IMG_5126.jpg

    The outlet of this cyclone is a rectangle of 18 x 29.5 cm so 531 cm2

    a.jpg

    And the 300 main line if I go the metal stuff is 706 cm2

    The current 200 mm inlet is 314 cm2

    So will it still work OK ? The limiting factor is the exit at 531cm2.

    I assume its just going to be a bit more free to suck a bit more and hopefully the dust still drops out into the drum or box I make .

    Rob

  14. #28
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    Tradelink or Eagles are the cheapest, Reece are far and away the dearest. Have you enquired about metal ducting? Or spiral metal?

    edit: ignore that I just read the last post. I have a similar system to yours except my machine is in a huge cabinet with hanging and swinging filter socks and a small drum at the bottom. I have metal ducting it works well and itís easy to unclip the sections and change it around. I have 250 mm main trunk and the volume that goes through is phenomenal, once it gets down to a gate and 100 mm it feels like much stronger suction but the volume is less presumably. One of the muppets that hang around the shed put his hand over the metal end of a gate and it cut a nice round circle into his skin and almost broke his fingers, so itís powerful. One thing I noticed that the efficiency improved when the joins in the duct were sealed with a wipe of silicone between the flanges. On the transitions and ones I thought I might move around I used a self adhesive foam tape about 1/4Ē wide around and it works well too.

  15. #29
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    I'm not the math wizard of others here but I plugged in some of your numbers into this calculator and changed from one size to the other.

    Using the 225mm PVC (10") with 100' of duct (close to 30 metres) and 2,000CFM for the air flow and no other factors like elbows I got 1.618" of water loss and a velocity of 3668 FPM. Repeating it and changing to 12" (300mm) Galvanized duct the result was .745" of water loss which is good but the velocity becomes 2547FPM which is not enough to carry the dust. You want at least 3500FMP for horizontal ducts and 4000FPM for vertical. So the PVC would work but the metal duct won't.

    Understanding your main lines might not be that long it does point to the bigger ducts being too big to carry the dust to the collector even if multiple ports were open. Bob or one of the more learned members can confirm. You might want to take a pass on the deal unless you can confirm it will work correctly.

    Pete

  16. #30
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    Quote Originally Posted by QC Inspector View Post
    I'm not the math wizard of others here but I plugged in some of your numbers into this calculator and changed from one size to the other.

    Using the 225mm PVC (10") with 100' of duct (close to 30 metres) and 2,000CFM for the air flow and no other factors like elbows I got 1.618" of water loss and a velocity of 3668 FPM. Repeating it and changing to 12" (300mm) Galvanized duct the result was .745" of water loss which is good but the velocity becomes 2547FPM which is not enough to carry the dust. You want at least 3500FMP for horizontal ducts and 4000FPM for vertical. So the PVC would work but the metal duct won't.
    An important factor to bear in mind is, unless other blast gates are kept open, it will be near impossible to get 2000 CFM thru most machines so in practice the volume might be closer to half that as will the air speeds so correct sizing becomes important.

    The nominal 3500/4000 FPM figures covers all types of sawdust, including large volumes of very large chips such as softwood coming off big machines such as a 24" thicknesser.
    Luckily In practice I've found even as low as 2000 FPM is enough for sanding dust, 2500 FPM is enough to carry bandsaw and table saw sawdust coming from a 19" BS and 12"TS, and 3000FPM is enough for a 10" thicknesser especially if chips are from Aussie hardwoods ie harder ie chips are generally smaller and even though they are denser the overall weight is lower.

    The problem is not just fall out, but the resuspension of sawdust that has dropped out inside dusting after a stalled/stopped air stream. Once that saw dust drops to the bottom of a horizontal pipe the resuspending it is what requires the higher air speed. Nevertheless I agree with QCs overall summary that going too large on the main might be a cause for subsequent regret.

    BTW 9" PVC is not 225mm - instead its closer to 240mm ID which while not that different to 300 mm but it will still be significant in terms of air speed.

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