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  1. #11
    arigram's Avatar
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    Light-tight ventilation

    Just as I expected, the exaust is not light tight.
    So, yesterday I bought a custom-made alluminum pipe to help with the matter. It still didn't make the system light tight even though the inside was painted black and the extension of the pipe is somewhat long. It must be the large opening (30cm diameter) that lets a lot of light in.

    I have included a photo of the outside of the pipe and a diagram of it. In pinkish purple I have drawn what I think two or three pieces of sheet would act as baffles to elliminate the problem.
    The alluminum corner is very expensive and getting another one apart from the cost would also mean that I will have to take the thing apart, take it back to the store and also its not a guarantee that it will work.

    What do you think?
    Will it affect the airflow too much?
    Do you have any other ideas?
    Last edited by arigram; 01-12-2008 at 07:51 AM. Click to view previous post history.
    aristotelis grammatikakis
    www.arigram.gr
    Real photographs, created in camera, 100% organic,
    no digital additives and shit




  2. #12

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    Dear Aristotelis,

    My impeller isn't light-tight either (despite being sold as such) so I have a plenum chamber on the outside: essentially, a box painted on the inside with blackboard paint and equipped with baffles (also blackboard-painted) so the air can be sucked in freely.

    At the other end of the darkroom I have an extractor fan venting into the space between the ceiling and the floor of the room above. The extractor is rated at a lower volume/minute than the impeller and is probably further constricted by the space into which it vents, thus resulting in a very, very slight positive pressure.

    Our darkroom is the old wine cellar, maybe 200 years old, and the big problem is humidity: it's built into the side of a hill. We have to run a dehumidifier constantly, which warms the room quite a bit. Very welcome in winter; very unwelcome in summer.

    There are pictures of the darkroom in the free 'our darkrooms' module in the Photo School at www.rogerandfrances.com. One of the tricks I'm quite proud of is the Nova
    slot processor recessed into the work surface.

    Cheers,

    Roger

  3. #13
    Steve Smith's Avatar
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    Another idea. What about placing some sort of fairly coarse dark foam into the pipe (a bit like a filter)? Something about 50 to 70mm thick and cut into a circle just big enough to fit into the pipe and hold itself in place. Obviously it does not want to be so dense as to restrict the air flow.


    Steve.

  4. #14
    DWThomas's Avatar
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    How about swiveling the existing ell to point upward and putting two more ells in to create an inverted U against the wall? All would painted flat black inside, ideally. You might want some sort of bracket or brace, or maybe just a fastener through the bottom edge to avoid it getting too wobbly.

    (Excuse the 1906 CAD ...)

    Dave T
    Attached Thumbnails Attached Thumbnails ArisVent.gif  

  5. #15
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    More thoughts.

    You could add one more ell on the bottom of the tube, ideally with the opening pointed north, or located such that it never gets direct sun.

    In addition, a diagonally cut section of pipe could be added to shade the opening.

    Obviously the more bends added, the more impedance to air flow, but I think this would be a reasonable compromise.

    DaveT
    Attached Thumbnails Attached Thumbnails ArisVent2.gif  

  6. #16
    Robert Hall's Avatar
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    They're right, you need at least one more bend.
    Robert Hall
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    Technology is not a panacea. It alone will not move your art forward. Only through developing your own aesthetic - free from the tools that create it - can you find new dimension to your work.

  7. #17
    arigram's Avatar
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    Another bend would cost a lot, can't I get away with it with three sheet baffles like I demonstrated?
    aristotelis grammatikakis
    www.arigram.gr
    Real photographs, created in camera, 100% organic,
    no digital additives and shit




  8. #18
    DWThomas's Avatar
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    Another bend would cost a lot, can't I get away with it with three sheet baffles like I demonstrated?
    Maybe -- I'm certainly no authority on this stuff. I was thinking the bend might be a standard plumbing item something like what is called "stovepipe" over here. I would think you could cut some cardboard baffles and tape them in the way you show in your drawing. That would likely not be a permanent solution, but it would provide a way to try the idea. Looking at your picture, it occurs to me you could surround the bottom of the pipe with a box or upside down trash can or similar enclosure. Have a hole cut in the bottom (now facing up) to snuggly fit the pipe and seal the joint with tape and some sort of black goop. Cut part of one side out of the box or can, maybe even put in a screen or louvered baffle. Then orient the opening toward that wall to avoid direct sunlight entering, leaving enough clearance from the wall to get good air flow.

    Just writing/thinking out loud here. I'm not a ventilation or darkroom construction wizard but those are ideas I would probably try.

    DaveT

  9. #19
    arigram's Avatar
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    Thank you Dave for your ideas.

    It seems in the end I only needed two alluminum sheets to act as baffles. Its completely light tight now.

    I only have one question:
    The frame of the exaust doesn't fit completely around on the wall. There is a metallic frame inside the wall though so it doesn't leak light or air and the fan doesn't "feel" those small openings on the frame.
    Do I need to fill them so the frame sits perfectly?
    aristotelis grammatikakis
    www.arigram.gr
    Real photographs, created in camera, 100% organic,
    no digital additives and shit




  10. #20
    DWThomas's Avatar
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    I'm not sure I follow you here. The outside looks well sealed in the picture. If it's inside, I guess one question is does it leave voids that open into the interior of the wall -- that might result in dust being sucked into the room.

    If it's a matter of the fan box/plenum or whatever not filling the wall opening, perhaps you could cut and fit some trim moulding around it, nailing it into the wall?

    Is it a structural issue -- does the fan assembly wobble? Perhaps some wooden strips could be wedged in as shims. If it's just a cosmetic issue, you could probably even use some sort of tape to cover the gaps and paint it to match the wall.

    So there's a few random ideas but I'm not sure if they address your problem.

    Anyway, it sounds like you are making progress. One of these days I need to do some work on mine.

    DaveT

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