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Creating Positive Pressure

  1. Aug 13, 2013 #1
    I am not an engineer which is why I have come to this forum.

    I am currently working on a project for my business. I am trying to create a box that needs positive pressure. My basic requirements are to keep out dust and lint from contaminating my work.

    There will be an opening on this box where the air will be leaving the chamber. This is the same opening that your hands will go through(I understand that my hands can contaminate the environment etc...). Talking with a friend I am under the impression that to create an environment with positive pressure the only factor I need to figure is the size of the opening. The volume of the chamber does not matter.

    My question is as follows. If my opening is 90 inches square(18x5"), how much filtered airflow is required? I know there is a measurement involving CFM which is cubic feet per minute. I have another friend who says I should use about 150 CFM. I don't think this is right because that rating doesn't associate with the opening. And 90 inches squared has no value of time.

    Can someone please break this down for me? I have been on google for a long time and I can't seem to figure this out.

    Thank you in advance!

  2. jcsd
  3. Aug 13, 2013 #2


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    Science Advisor

    I presume you look through a transparent window. The airflow must be sufficient to prevent air currents bringing external air back in through the hand hole. You can minimise the flow required by attaching a lint-free fabric shroud over the 18”x5” aperture, with fabric tubes attached for your arms and hands to pass through. Whatever pressure you have will then bleed between the shroud and your arms. The better that fit, the less the flow required. At this point you should experiment with a shroud and a small fan.
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