Ventilation Arm

[Henry Yorke]

Hi, everyone.

I'm exploring some options for more ventilation in my darkroom - and was wondering if anyone know of or has experience with a ventilation arm - the kind that could be swung around and positioned over specific trays, etc. I've seen welders use them - but I don't know of any darkrooms that have them - probably because they are darned expensive. Nonetheless, I'm curious....

[lenser]

If you are talking about venting the fumes from your sink area, an old Kodak darkroom design book from decades ago showed a very simple system where the width of the sink featured a sort of boxed in back splash that ended a couple of inches above the top of the sink. The back was offset from the wall by two or three inches and connected to a simple vent fan at the top so that it would draw air across the entire sink and up into the fan and thus out to wherever it was exhausted. I'm going to build that concept into my next darkroom.

The vent arm type of system I have seen in old Calumet and other photo lab stainless steel catalogs where it was shown in use in the mixing area of commercial darkroom/labs and positioned over huge chemical tanks while the actual solutions were being mixed. Those were very high volume air handling systems with big hoods that covered most of the space over the tanks while power propeller type of shaft mixers were doing the blending.

[Drew Wiley]

They're super easy to make. I just used some chem-resistant corrugating ducting with an overhead suspension. Then this taps into the top of my fume hood,
but with an inline booster fan which can optionally be used if it's some kind of fumes I'm particularly wary of. Just to to any HVAC supplier like Grainger. Dryer
ducting is too fragile.

[Drew Wiley]

... got interrupted. At the end of the hoses I use simple PVC irrigation pipe fittings, which have all kinds of nice shapes. I can position the hose right over a bottle
of noxious whatever, alternately pop it onto a length of upside-down vinyl gutter with a mating fitting (which acts like a linear mini-fume-hood over my drum processor), or alternately clip it up and out of the way. But you do need to vent it outdoors and have makeup intake air, just like any working system. In my case
I just team it up with my main fume hood. No need to spend much. Even with a squirrel-cage booster fan in line, you could do this for a hundred bucks (not counting light traps, main fan, etc - but as an attachment to any main system). Don't use a propeller fan in an inline ducting application - air pulls far better than
it pushes.

[Henry Yorke]

Thanks, Tim & Drew for your thoughts.

Drew - if it's not too much bother, would you be able to post a couple of pictures of your set-up when you have a moment?

[Dan Dozer]

Hey - something that I actually know something about! To start with, a back draft system that lenser describes will be relatively ineffective unless you have a whole lot of exhaust air moving through it. You need a forceful exhaust airflow in order to pull the air into it, and the size of fan that any of us would be considering for an exhaust of this type will not be any where large enough to really work. The thing to consider when you are designing/building your own is that the larger the exhaust opening, the much larger the exhaust fan needs to be. An exhaust source above your sink will normally work better than a backdraft. Even then, your exhaust opening works better if it is closer to your sink/trays than higher above near the ceiling. An over head adjustable arm that you can get relatively close to the offending fume source will be the most effective. As others have said, not too difficult to design and build yourself. Here is a commercial company that makes these things. The ones at the top of the webpage are for big welding applications, but those smaller ones at the bottom of the page might give you some ideas to consider.

http://fumex.com/movex/local-extractors-us/

[John Jarosz]

+1 on what Dan said 100%

[Drew Wiley]

OK - good point. That is why my localized flex fume attachment attaches to the main fume duct, which in turn is connected via light-tight ducting to a big commercial exterior wall-mounted variable-speed squirrel-cage fan. This isolates all the noise outside, yet is inherently quieter than propeller-type fans. Since
everything has to be light-tight, including the intake air vents, a darkroom inherently needs more CFM pull than just a bathroom fan designed for the same size area, for example. And even though I normally run this main fan on its lowest setting, I can instantly turn it way up for something nasty, like diluting glacial acetic
acid or some hypothetical spill on color chemistry. The booster fan itself is a bit noisy, but it's only used momentarily, over a beaker of nasty chem, for instance.