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Thread: Question about air speed of dc exhaust

  1. #1
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    Question about air speed of dc exhaust

    With all other variables common , would increasing the speed of the exhaust cause improved dust removal, or would it do the opposite?

  2. #2
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    Your question is a little confusing because "speed" probably isn't something you can change, more or less.

    Assuming a cyclone with the blower post- separation, reducing the hopefully already minimal restriction behind the blower by up-sizing to the filters or to a direct vent a little is certainly a good thing, but there will not be a substantial difference if you go up a little vs a lot unless the length of the path is really long. So if the unit is in a closet and you're designing your return to shop air, you want generous (and indirect) and if it's a long pathway, a little larger is good. You do not want the return to "pressurize" in a sense.

    My Oneida cyclone has a 7" inlet and an 8" outlet, for example. My return to the shop exceeds the cross-sectional area of the 8" duct that goes to the filter. Any restriction is from the filter, not the duct or the air return to the shop.
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    The most expensive tool is the one you buy "cheaply" and often...

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    No, I didn't make sense. I wanted a purely honest and accurate responce to what may very well be a really dumb idea.

    What if a person was to create venturi entry points in the exhaust duct and use some compressed air or, perhaps they will provide the increase in air speed all by themselves.
    Or will they simply do nothing?
    I'm thinking jet pump, I suppose.
    As always, mockers welcome.
    Is it a dumb idea?

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    I am referring to no filters and simply a pvc exhaust pipe to the outdoors.
    Tuned headers are situated in such a way that each pipe helps pull exhaust out of the pipe in front of it.
    Compressed air couldn't be too difficult to harness. It's used (or at least used to be) to press the clutchplates together on 10,000hp top fuel cars. And to look at the size of the actual compressed air bottle on one , you'd wonder how such a small tank could handle that task with ease.

  5. #5
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    Quote Originally Posted by Bill Jobe View Post
    I am referring to no filters and simply a pvc exhaust pipe to the outdoors.
    Tuned headers are situated in such a way that each pipe helps pull exhaust out of the pipe in front of it.
    Compressed air couldn't be too difficult to harness. It's used (or at least used to be) to press the clutchplates together on 10,000hp top fuel cars. And to look at the size of the actual compressed air bottle on one , you'd wonder how such a small tank could handle that task with ease.
    Using highly compressed gas (2000 psi nitrogen in your example) in a cylinder acting against a piston is as comperable to dust separation in a centrifugal separator as apples and squirrels. You’d do better to just trust the folks that have established successful businesses building and supplying dust collection systems than to keep trying to reinvent the wheel.

  6. #6
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    Scathing retorts welcome, as well.

  7. #7
    With the same cross sectional area of the exhaust increasing the velocity of the exhaust would have the same effect as decreasing the resistance of the exhaust, it would increase velocity of the inlet. But I am not sure that would be the impact of injecting compressed air into the exhaust. The velocity of the total air would increase but there would be more air to move so it would have to. I think it would increase the back pressure on the DC.

    DCs are designed to move a LOT of air against very little resistance. Vacuums, including shop vacuums, move much less air but can do so against considerable more resistance. Due to their design, the goal with DCs has to be to keep resistance as lot as practical. Big tubing, minimized flex, clean filters with a lot of area or no filter. Cyclones hurt but not as much as a dirty filter. Only limit on lowering resistance is to keep air velocity high enough to move the debris.

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