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Airflow question

  1. Feb 4, 2008 #1
    I'm setting up a dust collection system for my garage woodworking shop. My plan is to build a manifold for various tools to feed into, with a single 4" exhaust port connected to the dust collector. This manifold is an 8" square by 5' box, with 4", 2 1/2" and 1 1/2" hoses going into it. All unused hoses will be blocked off by blast gates on the manifold. My question is: Do the dimensions of this box make much difference to the airflow at the tool? I know the airflow inside the larger volume box will slow, so that's why I'm putting the exhaust at the bottom. I think the air speed should pick up again in the narrower hose to the tool, but I'm not sure. I could make the box cross section only 5" square if I had to, but 8 is more convenient. Do you think it matters to performance?
  2. jcsd
  3. Feb 4, 2008 #2


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    Staff: Mentor

    By definition, the dimensions of the manifold make no difference in the performance (the point is that it has to be a fair bit larger than the sum of the sizes of the hoses going into it). However, as the airflow is slower inside the box, it will work as a dust separator - the dust will collect at the bottom of the box.

    One other issue - if you consider how much airflow there is to get a vacuum cleaner working, you're talking about needing a pretty big fan.
  4. Feb 4, 2008 #3


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    Gold Member

  5. Feb 4, 2008 #4
    Thanks, Russ. I suspected as much, but wanted to be sure before investing the materials and effort. The dust collector is a 1 HP Delta model with a lower bag for chips and shavings and an upper bag for finer particles. It's good for one tool at a time, which is why I'm trying to minimize airflow losses to leaks and friction. The hoses and manifold will be well grounded inside and out. It's not something I want to build twice, so I appreciate your help in getting it right the first time.
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