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  1. #1
    Join Date
    Jan 2012
    Location
    Toowoomba QLD
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    62

    Default Blast gate positionsi

    Hi All,

    I would like some help with positioning my blast gates on my dust extraction system. I am about to change my duct work and wondered where you guys are putting yours. As per the attached photos I currently have them all very close to the dust extractor as I always thought this would cut down on lose of suction.

    i am using 100mm pvc pipe for duct work. Some have the blast gates next to each machine but I always thought if the system has to constantly suck air from the hole duct network, this would cause loss of suction. Currently I have to walk to the dust extractor, switch around the blast gates to which machine I'm going to use, turn on the extractor, then walk back to that particular machine to use it. This process is then reversed when I'm done to go the next machine. I'm getting tired of this!!

    do you guys have a better way? See photos. Yes..... In know, I shouldn't have dust extractor inside my shed.

    image.jpgimage.jpgimage.jpgimage.jpgimage.jpg

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  3. #2
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,757

    Default

    The best place for blast gates (BG) are as close as possible to the junctions of ducting to a main/truck/other line.
    This is as shown below on duct 1 by BGb opposed to BGa
    BGposns.jpg

    With a BG at BGa, if another machine machine is used for a long time further back along the trunk line, and Machine 1 is not used, the air constantly moving along the trunk line past the junctions of Duct 1 will generate a slight vacuum in duct 1 and deposit sawdust in duct 1 down as far as BGa. Then when you go to use machine 1 your DC may not have enough suck to lift all the sawdust blocking duct 1. It only happens if you leave the machine1 duct unopened for a long time. If you want to avoid this you can always open all ducts up when you are finished any use of the DC to clear any possible blockages.

    If you have ducting that is too high up and out of the way and you cannot reach BGs that are up that high you have a number of alternatives

    1) Use a rocker style gate. (see here Ducting update.)
    2) Use a pneumatically operated gate.
    3) Use a 180º take off as shown for Duct 2 above. This of course has a 180º turn and longer ducting, so will be slightly more restrictive to flow.

    Another possibility is the sort of setup below which allows you to open an inspection cap and if necessary shove a compressed air line up the inspection point to clear any blockages.
    I had this on my old DC system and it worked but it makes a big mess.

    Ducting2.jpg

    On your set up below to avoid the above problem the only thing I would consider is adding a gate as shown (green line).
    This of course only matters if you use the machines on the RHS of the picture for a long time to the exclusion of those to the LHS.

    BGresp.jpg

    BTW you do realise those black plastic BG are highly restrictive.
    The are 94mm ID and while it does not sound much different to 100 mm they restrict flow by around 12% compared to a 100 mm.

    Correctly sized BG are dead easy to make - check out some examples in the thread I refer to above.

  4. #3
    Join Date
    Jan 2012
    Location
    Toowoomba QLD
    Posts
    62

    Default

    Hi Bob. Thank you for the information. Along with those blast gates, do you think I should be using bigger ducting?

  5. #4
    Join Date
    Feb 2006
    Location
    Perth
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    27,757

    Default

    Quote Originally Posted by Dez Built View Post
    Hi Bob. Thank you for the information. Along with those blast gates, do you think I should be using bigger ducting?
    Absolutely but it only really makes sense if "these 4 ducks are lined up"

    1) 6" ducting
    2) Modify the DC accord to the Generic 2HP DC modification sticky in the Dust forum
    3) Open up the ports on the machines to 6" or use multiple 4" ducts on the machines.
    4) DC vents outside the shed

    The 4th one is a must, whatever you do.

    If you only do one or two of the first 3 you wont get anywhere near the benefit of doing all 3.

    However, I can appreciate that not everyone is as fanatical as me and you may want to do your upgrade in stages.
    e.g. you are going to change your ducting so why not do it in 6" - as it will save you the headache alter.

  6. #5
    Join Date
    Dec 2015
    Location
    Kiewa
    Age
    64
    Posts
    138

    Default

    Bob, not sure about your pics. Ducting Y appears to be going backwards?????

    My own experience is that you need 200mm main line ducting to service cyclones vented outside (easy for me on 9 acres). Blast gates on the main line, then down to 150mm.

    As Bob L has said, you create dead spots on your main line unless you use BGs to limit it.

  7. #6
    Join Date
    Feb 2006
    Location
    Perth
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    Default

    Quote Originally Posted by Jeff Leslie View Post
    Bob, not sure about your pics. Ducting Y appears to be going backwards?????
    No that is how they should go,
    Where possible the air should enter the main trunk at a less than 90º to the direction of the oncoming air in the trunk line

    Do you mean for duct 2?
    From machine 2, that duct is going up and over the trunk line before it joins.
    Like this.
    Trunk is the horizontal duct on the RH wall and air direction is heading out of the picture.
    completeducting.jpg

  8. #7
    Join Date
    Jan 2012
    Location
    Toowoomba QLD
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    Default

    Thanks Bob.

    I was was going to get one of those pleated filters for the top instead of the felt bag. But then I realised I would be better off drilling a hole through the side of the shed and venting outside. Might put some sort of filter on it outside to keep dust down as I'm in suburbia

  9. #8
    Join Date
    Feb 2006
    Location
    Perth
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    Default

    Quote Originally Posted by Dez Built View Post
    Thanks Bob.

    I was was going to get one of those pleated filters for the top instead of the felt bag. But then I realised I would be better off drilling a hole through the side of the shed and venting outside. Might put some sort of filter on it outside to keep dust down as I'm in suburbia
    Venting the DC outside is the single best thing for lowering fine dust levels.

    Bear in mind that a Pleated filter has the advantage that the filter takes longer to clog up so does maintain better flow for longer.

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