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Duct sizing chart - pressure loss

  1. Jun 30, 2013 #1
    I found this sizing chart for ventilation ducts. Notice the gray area for what I suppose is the accepted pressure loss area. What I wonder is why it changes as the sizes pass Ø800. From here on the upper pressure loss limit goes down to 0,7 Pa/m. Is this because of velocity issues or something else?

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  2. jcsd
  3. Jun 30, 2013 #2


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    Staff: Mentor

    That's something I should probably know, but I don't. It could be an issue of duct strength, economics, noise. I'm really not sure. I use a duct sizing calculator (rotary slide rule, basically) which has no similar markings. where did you get it?
  4. Jul 1, 2013 #3
  5. Jul 1, 2013 #4
    I'm pretty sure it's a limit on velocity, and not on pressure losses. 200,000 l/s of gas rocketing through a pipe at 40 m/s is not within typical design limits.
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