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Thread: modifying discharge of dust collector... blast gate sources??

  1. #1
    Join Date
    May 2009
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    black river falls wisconsin
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    931

    modifying discharge of dust collector... blast gate sources??

    I want to vent my dust collector outside all summer and in winter when using my wide belt sander. I want to put y fitting in discharge of my 2 cycle dust collector so can go to filter or outside by opening one gate and closing the other... need gates that will not leak. thinking maybe plastic self cleaning gates would work but cant find source in 8". I used metal gates from blast gate company for most of my system but would leak if put them on the discharge side of system. Looking for sources or maybe different approach to solution.

    Thanks
    Eugene

  2. #2
    Join Date
    Feb 2003
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    McKean, PA
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    I made my own blast gates out of some 3/4" wood and some 1/4" thick lexan. I cut wood squares about 2" wider and 4" taller than the outside diameter of my pipe. Then I cut a circle in the blocks 1" in from the bottom and the sides so they fit over the duct pipe. I sandwiched the lexan between the two blocks and marked the cover paper for the circle opening. I removed the lexan and enlarged the circle by 1/4" all the way around and then extended it toward the top to make a U shaped cut. Once I cut the lexan U, I put the sandwich back together leaving teh cover paper on the outside part and removing the paper from the inside part of the U. This creates a small clearance so the inside part of the U will slide. Put a 1/4" sheet metal screw about 3/8" up from the bottom of the center of the U to keep it from pulling all the way out of the sandwich. I put silicone on the ends of the pipe and pushed it into the holes on each side. Let is set up and your blast gate is in place. They seem to work pretty well.
    Attachment 302317
    Last edited by Lee Schierer; 12-19-2014 at 3:20 PM.
    Lee Schierer
    USNA '71
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  3. #3
    Join Date
    Sep 2012
    Location
    Mnts.of Va.
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    Eugene,this is gonna sound a little left field but here goes.........

    Look in the yellow pages and see if you have a sheet metal roofing co....and arguably an HVAC joint...that would qualify as "old school",near you.HVAC biz has gotten to where they don't do a whole lot of fabricating these days(think CAD systems,ordering ducts,yadayada).But if you have an old roofing co local to you.....man,I'd go down there(mid week)and find the oldest shop guy there and ask him for advice.Tell him what you're thinking and see what he has to say on the subject of quick change fittings/dampers that seal really well.Have whatever specs(your duct size/sq ftg/etc),"in hand".You might be suprised what,and how cheaply they can fabricate exactly what you need.

    We're very fortunate here.....our,"go to roofing guys" have not only been in biz for over a hundred years,they're still in the same dang building.Kinda neat really,the 20th century surrounded them and they never moved.....now there's bars,condos,restaurants,etc....all around them and they just keep it going.I love going in there.The "old man"(he must be 80+)is a crotchety old cuss,but he's an absolute hoot and loves when I come in there with something out of their normal scope.best of luck,BW

  4. #4
    Join Date
    Feb 2003
    Location
    Washington, NC
    Posts
    2,387
    Eugene- I think you already figured out what Lee missed- a blast gate that works fine on the intake side of your DC which is under negative pressure, will leak, possibly badly, and allow dust to spew dust into your shop if located on the discharge side of the blower since it is under positive pressure. The dust-laden air will seek the path of least resistance, so the amount of blast gate leakage will depend on the gate blade to gate body clearance and the back pressure generated by the amount of ducting when set to discharge outside or the design and condition of the filter when set to recycle air back to your shop.

    You'll want totally-sealed, possibly-ganged, parallel (side by side) gates or a sealed diverter. In both cases the gate/diverter actuator will need to pass though an air seal. That isn't too hard to do if you use a round pull rod or pivot shaft in a close tolerance hole or hole with o-ring seal. Also, it doesn't really matter if the gates or diverter leak internally- when discharging outside some air could flow to the filter or visa versa.

    Here is a cross-sectional view of a simple diverter that can be made from MDF, ply, metal or acrylic if you want to see what is happening. The only part that passes through the diverter body and must be sealed is one end of the pivot rod which is attached to the diverter. Note, in this design it can take considerable effort to move the diverter if the DC is on.

    Last edited by Alan Schaffter; 12-21-2014 at 1:31 AM.

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