Page 3 of 3 FirstFirst 123
Results 31 to 35 of 35

Thread: DC duct sizing

  1. #31
    Join Date
    Apr 2017
    Location
    Michigan
    Posts
    404
    To do this even halfway right (working with what you have) still requires some easy math.

    1. The chart is a start but it doesn't address friction rate. It does show FPM. More velocity in the duct will use more energy and reduce CFM but too little velocity will let solids drop out. 4000 FPM is enough to carry sand so it should be more than enough for dust.

    2. Each fitting has a friction equivalent to so many feet of duct. This all gets added up to a total equivalent footage and multiplied by the friction rate to get a pressure drop for each length of a given size and flow. Pretty straightforward so far. It gets messy when you open and close blast gates.

    3. You need a fan curve, which you will have to correct for the inlet condition since you are altering that. That done you can determine how many CFM your system will move for each combination of blast gate settings.

    4. Let's not forget the motor. It may not handle the load the fan will put on it. Deleting the filter and opening too many blast gates could overload it.

    For your homespun design you will get something. Not sure what.

  2. #32
    This is the only thread I've found about designing dust collection for a group shop with more than one gate open at once. We are in a Seniors hobby workshop and have ordered a Clearvue CVMax to handle 6 machines. We are planning an 8" main duct with 6" drops. 1. Does the recommendation to have area of ports equal area of duct hold true when 2 or 3 gates might be open? Should duct size be reduced toward the end of the run? We do not have the resources to hire professional duct design so are researching this as best we can ouselves.

  3. #33
    Join Date
    May 2005
    Location
    Highland MI
    Posts
    3,372
    Blog Entries
    11
    Quote Originally Posted by Joe Jensen View Post
    Look inside the machine to see how small the opening is at the point of collection. This is the true port size for your machine. Also see the post in the stickies above for good info on dust collection duct design. Sadly the real port inside the machine is the limiter for nearly all of us.
    Don't be afraid to go up one size from the port area when sizing the machine-to-main duct. The velocity through the port will equalize with the air flow through the duct. Larger ducts will allow more airflow through the port which acts as an orifice.
    NOW you tell me...

  4. #34
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
    Posts
    46,903
    Quote Originally Posted by Susan Lamb View Post
    This is the only thread I've found about designing dust collection for a group shop with more than one gate open at once. We are in a Seniors hobby workshop and have ordered a Clearvue CVMax to handle 6 machines. We are planning an 8" main duct with 6" drops. 1. Does the recommendation to have area of ports equal area of duct hold true when 2 or 3 gates might be open? Should duct size be reduced toward the end of the run? We do not have the resources to hire professional duct design so are researching this as best we can ouselves.
    Susan, a multi-worker shop system is absolutely going to require "more math" when it comes to sizing your drops so that you don't detrimentally reduce air flow speed/volume below the point that you stop collecting. Dust collection is 100% about air flow. 6" drops everywhere with too many multiples open "may" not be practical for a "smallish" (compared to many commercial units) dust collector. Oneida does designs and if one buys the duct material from them, the cost for the design may be mitigated. Other suppliers may do the same.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #35
    Join Date
    Dec 2006
    Location
    Toronto Ontario
    Posts
    8,941
    Susan, I suggest you check with the authority having jurisdiction in your area.

    It could be the town planning department or the fire department.

    Where I live a system with those characteristics has to meet specific fire prevention requirements and be designed and inspected by a licensed engineer.

    regards, Rod.
    Last edited by Rod Sheridan; 11-14-2018 at 5:12 PM. Reason: Spelling

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •