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  1. #1
    Sean's Avatar
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    Is my ventilation doing anything?

    Ok was working in the darkroom all night (again), and tonight put in my light tight intake vent. So one end of the room has the intake vent and the other side of the room has a big Doran darkroom fan sucking air out. Now it's supposed to move a lot of air, and when I go outside i can feel a steady flow of air coming out of it. It's not like a blower vac or anything but you can feel a decent amount. What I'm not sure of is how much air is being moved. Since I was doing construction in there all night it got very dusty. So I cut the lights and shined a flashlight near the exhaust fan. There were very fine dust particles flitting all around it but not even getting sucked out. I thought everything fairly close to the vent would be getting sucked out big time but it felt like it was doing absolutely nothing. Is this normal or have I done something wrong? Is it moving air in a way that I'm not realizing? I also thought I would feel a light air coming in through the intake vent but even with my face right to it I felt nothing. The room is air tight and the intake vent was exposed to the outdoors. Can someone shine some light on this for me? Thanks

  2. #2
    Laurent's Avatar
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    Sean,

    I guess that if the light proof intake is build with several "gates" (sorry, my English is not good enough for the darkroom vocabulary) (let's say that as light -usually- does not bend, it would be enough to have a kind of Zs in the path of the air to let air in and keep light out) then the dust would "fall" between the gates and would therefore not cross the intake.

    If you feel a steady flow, then I'd assume the air goes through your darkroom by some path.

    Did I miss something ?
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  3. #3
    noseoil's Avatar
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    Sean, try using a lighter and "flick your bic" in the darkroom in front of the intake to see which way the flame is moving. You should see a movement of air. Similarly, there should be the same movement, in the opposite direction, near the exhaust fan.

    P.S. Don't use this trick to test for gas leaks, use soap suds. Don't use soap suds to test for darkroom leaks. tim

  4. #4
    rogueish's Avatar
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    If your standing outside and you feel the air coming out, then the fan is working. If your standing inside and don't see the dust leaving, then it's possible the air being "sucked" out is not all from inside. Can air from inside the walls and outside the room get "pulled" out? Check on air tightness of fan to wall seal. Is the exhaust port bigger or smaller than the intake vent? If the intake vent is large and the exhaust port is small (or smaller) then you will notice a difference in "pressure" between the two. I would say that if it's not pulling out the dust in front of the exhust port, you have an air leak (as opposed to light leak ).
    Wet your hand or hold a light ribbon on the outside of the exhust port, then do it again on the inside of the room in front of the exhust port. you should feel/see the same amount of air. If not, your fan is pulling air from another source.

  5. #5

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    Get some type of perfume and spray it into the room without the fan moving. Turn on the fan and see how long it takes to remove the smell. It is what we used in the Darkroom I used to work in when the new hood was installed. Worked like a charme.

    Dust is a nasty beast. It resists everything that has been created to move it or get rid of it. It's only purpose is to ruin what you are doing. The only time it will actively head in any one uniform direction is when you are printing or you are loading a film holder. Other than that it just sort of swirls working up energy in the great microbial mosh pit.
    Technological society has succeeded in multiplying the opportunities for pleasure, but it has great difficulty in generating joy. Pope Paul VI

    So, I think the "greats" were true to their visions, once their visions no longer sucked. Ralph Barker 12/2004

  6. #6
    Robert Hall's Avatar
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    You might open the door to the room and see if the air flow increases out the fan exhaust.
    Robert Hall
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  7. #7
    Flotsam's Avatar
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    Quote Originally Posted by mark
    Get some type of perfume and spray it into the room without the fan moving. Turn on the fan and see how long it takes to remove the smell.
    And then try to convince your wife that you aren't entertaining ladies during the hours that you spend locked in that room.
    That is called grain. It is supposed to be there.
    =Neal W.=

  8. #8
    rbarker's Avatar
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    Quote Originally Posted by Flotsam
    And then try to convince your wife that you aren't entertaining ladies during the hours that you spend locked in that room.
    Yeah, I think I'd use aftershave instead.

    Oh, wait. That might be even worse!

    As others have suggested, Sean, it's probably a matter of making sure that there is enough available air in-flow to match or exceed the capacity of the exhaust fan. If the in-flow is restricted, the fan will pull air from wherever it can find it. In addition to doing the flic-your-bic test at the exhaust port inside the darkroom, you might do the test on the darkroom side of your air intakes, too. Essentially, I think you want to make sure that the air in-flow is well filtered, and sufficient to satisfy the exhaust fan.

    Additionally, you may want to compare the volume of the darkroom to the fair-flow rating for the fan. They usually have a rating measured in CFM (cubic feet per minute). A 10' x 10' darkroom with a 7' ceiling would have a volume of 700 cubic feet, for example. A 100CFM fan would then take 7 minutes to theoretically exchange the entire air volume in the room. Depending on the location of the air intakes, however, you might have "stagnant" air in corners and such that never gets moved.
    [COLOR=SlateGray]"You can't depend on your eyes if your imagination is out of focus." -Mark Twain[/COLOR]

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  9. #9

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    Quote Originally Posted by Flotsam
    And then try to convince your wife that you aren't entertaining ladies during the hours that you spend locked in that room.
    Hush up!!...She's buying it so far.
    Technological society has succeeded in multiplying the opportunities for pleasure, but it has great difficulty in generating joy. Pope Paul VI

    So, I think the "greats" were true to their visions, once their visions no longer sucked. Ralph Barker 12/2004

  10. #10

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    need more direction

    Just another thought. With a large darkroom, the volume of air could dilute the affect of the fan.

    The air going out of the vent, could just as easily be coming from the ceiling area as from across the chem trays. Or even a two deg change in air temp could keep the fan occupied for minutes (see where this is going?) It may be necessary to consider a hood above the trays to direct the airflow exactly where it's needed? (I know this would be more hassel!!)

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