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Thread: DUST collection question????

  1. #1
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    DUST collection question????

    ok i think charlie plesums answered my last one which was to try and gain some dust collecting power by adding a collector to between the the existing one and the tool i want to be collected better on.. so after seeing that steve southwood and bob gibson are looking to gain some cleaner air... i thought i might have come up with another solution.. what if i attached a second motor and impeller setup on the same set of duct work and had to exhausts.. another words have a 8" y and draw from it with 2 impellers going into two separate exhausts.. would that give me more draw at the tools or not? i really would like to get some more draw at my drum sander..
    If in Doubt, Build it Stout!
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  2. #2
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    My mind swims each time somebody tries to explain using two impellers on one set of ducts.... usually involved with turbulence in the airflow, etc. that messes up things. How good multiple fans works seems to depend on luck.

    If your sander is the Woodmaster 38 inch like mine, note that it only has one 5 inch dust port, only about 19.6 square inches. I have mine connected to a 6 inch duct that goes into the plenum close to my 5 hp cyclone. Probably close to the best suction you can get through a 5 inch port. The dust collection is better than it was before, but certainly could be better. Other 37-38 inch sanders seem to have 3-4 4 inch ports or 37 to 50 square inches (I am oversimplifying to add together the cross section, but it is a rough estimate.) Therefore I don't expect to ever get "great" collection on my drum sander.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

  3. #3
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    yup thats the one charlie so what your saying is that we wont get much better than what we have unless i parked one right next to it for it alone..
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  4. #4
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    Even that won't help, Larry. My 5 hp cyclone is parked next to the sander, and dust collection is imperfect (FAR from perfect) even with all the other ports closed.

    Occasionally I think about cutting in more dust ports, but then I go back to woodworking.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

  5. #5
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    Two blowers will likely fight each other and prematurely burn out one (or both) of them. There is only so much air you can pull through a duct before the vacuum goes up beyond the capacity of the blowers. Two blowers doesn't appreciably overcome much more static pressure if they're not designed for it already. That is, the static pressure in the ducts remains the same so unless you add a blower that can handle higher static pressure, you aren't gaining much and two would just fight one another since vacuum is ... there's a term for it ... I can't think of it now but basically it sucks in every direction so if blower #1 is pulling down 11" of vacuum in that duct, it means it's pulling that in the other blower, too -

    they don't pull together like two guys on a single rope - it's more like two guys pulling two ends of a split rope each at 45 degree angles to the "load" - each puller will be expending a good deal of energy straightening the rope in their direction and they end up fighting one another. That's a bad example, but hopefully ya get the gist
    Jason Beam
    Sacramento, CA

  6. #6
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    yup got it jason kinda like dragin out a deer and the frnt guy isnt pulling the guy closest to the deer is

    so quess i need to get me a larger impellor and do some revamping this summer
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  7. #7
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    Larger duct work will probably have a negative affect on your systems as air velocity will drop while maintaining the same volume of air moved. More DUST might very well remain suspended using a smaller duct thus HIGHER velocity which can get it "in the bag" My understanding is that the air MUST have a velocity within the pipes - at or above - 4000 feet per minute, to keep dust suspended and eventually sucked through your system. Charlie you clearly have a handle on this issue, I hope I haven't made things more confusing. Bill

  8. #8
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    I believe that the higher velocity is required to carry the heavier chips, but the finer dust will remain suspended with lower velocity.

    One of the interesting issues is the need to open additional ports to keep a good airflow if you have large ducts. For example if I just have one 4 inch port open on my 5 hp cyclone (such as at the planer, which only has a 4 inch dust port), the air flow is poor until I open an additional port (such as at my bandsaw) to allow more air to flow in the 6 inch pipe that is downstream from my planer. Until that extra port is open the cyclone sucks hard but doesn't have the air to move.

    How much suction can you get? I have a Clearvue cyclone, with the recommended 6 inch hole in the top of a metal trash can. I collapsed the metal lid, apparently when I didn't have enough ports open. I have now replaced it with an MDF lid.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

  9. #9
    Static pressure is the enemy here. Every impeller pulls less cfm as resistance- SP- increases. Adding additional impellers in parallel won't increase cfm in the same pipe unless the first is sized way too small which is almost never the case. In theory you could connect them in series but there are a million complications in getting that exactly right. Resistance goes up fast as velocity increases and most impellers are designed to operate under low pressure so as not to overamp the motor. High pressure blowers are loud, less efficient at low pressure but way better at high. Generally the higher the velocity the better the system will work. Although find dust needs less speed to stay entrained in the pipes, it needs more velocity to separate effectively in the cyclone. The clearvue, which is the best designed hobby unit, is designed to separate fines best at 6000 fpm entering the cyclone. Unless you are venting outside it's not just about picking up the dust but separating it before it gets to the filters. The cleavue 16" was originally developed for 50 hz overseas markets and delivers about as much flow as the 18" diameter cyclone can handle at 1400+ cfm. Dave

  10. #10
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    Larry, On my 725 planer/molder it had a single 6" line for dc. Even with a 3 hp dc right above it it would not pull the fine dust. I changed it out and put two 5" line on the top and it made a huge difference. I also did some other mods to help airflow.

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