Sink-level ventilation

[cyrus]

I am reconfiguring my darkroom and am considering options for sink-level ventilation for a 6-foot sink. Can anyone tell me if these pvc pipes which are connected to the exhaust at one end, and sealed at another, with a series of holes drilled through along it, actually work? Wouldn't there be no real suction left at the end opposite to the fan? http://myphotographydarkroom.blogspo...-air-vent.html (not mine, just randomly found image to use as an example)


The traditional solution for sinks that are pressed against the wall is to have a vent pipe run vertically down the center of the wall behind the sink, and attach it to a cowl/hood that spreads over the sink. In my case though, I can only vent to the right side of the sink and I'd rather keep the wall behind the sink clear of any pipes and tubes etc. so I am considering running a vent pipe over the back edge of the sink and out the side, as seen in the image above. I'm concerned though that the suction would not be even.

And more importantly, wouldn't it be better to have "point source" ventilation, like a 4" flexible wood-shop dust collector hose that can be pointed at specific areas/trays for removing the gases, rather than a broad ventilation over the entire 6' sink?

[Joe O'Hara]

I have not actually tried this, but looking at it, my guess would be that for such a pipe to remove significant amounts of air from
the sink area would require quite a lot of vacuum and as a result be pretty noisy. I am also skeptical that you would have anything like even airflow across a pipe like that due to the pressure (suction) drop.

Have you considered the volume of your space, and provisioning inlet and outlet fans that would turn the air over every 10 minutes or so? If you could manage that, you may not need to do anything special over the sink area.

If it is the acetic acid or fixer specifically that gives you trouble, others here may suggest alternatives that are less irritating (e.g., citric acid for stop, alkaline fixer).

[Jim Jones]

For efficiency, the holes should be large enough that they scarcely impede the air flow. Perhaps the sum of their areas should be close to the area of the pipe. For even air flow along the length of the sink, consider smaller holes near the exhaust end. You might also want larger holes near the stop and fix.

[cyrus]

Actually my particular darkoom is quite large and airy since I'm in a warehouse basement with 11" ceilings, only do b&w, and the darkroom is attached to a 20x30 ft studio space with regular ventilation, thus far I've just needed a fan to blow the air away over the sink to dissipate in the large space, and i never smelled anything (course, my nose may have become immune to the smell of fixer too) My stop is diluted white vinegar, which at worst smells like a salad.

But as more and more students/other photographers are using my darkroom and the output has increased I feel it necessary to provide additional ventilation for right over the sink to suck the stuff out and not let it just dissipate inside. I don't want anyone complaining about exposure either.

I can vent easily to the building air shaft right behind my sink by punching a hole through the 4" terracotta block wall, mounting a 4" centrifugal fan, attaching it to an elbow and then the pvc pipe with holes right over the sink. Since the ducting length is minimal and there is only 1 turn, 400 cfm should be plenty for a 6' sink. I understand that the size/placing of the holes has to be altered along the length of the pipe so as to maintain even airflow/suction -- but why ventilate the entire length of the sink at all, if you can point the vent particular trays/source of gases using a dust-collector type flexible corrugated 4" plastic pipe, and then fold-up & put the fleixble pipe away when not generating smells? Wouldn't that make more sense as far more efficient in removing gases in darkrooms ? Can anyone see any problems with this? After all, there's no reason to vent the wash tray, the fixer and stop are what generate the sulfides

[HMG]

The problem with a hood over the sink is that it draws fumes past your face. And, unlike a stove, you don't have heat to lift the fumes. So they'll rise, but not as easily.

I've seen darkroom designs with the ventilated pipe at tray level and suspect that's the best approach. But I'm not sure those designs have been tested, much less optimized. I think your approach is good, here's what I would do:

• Do your pipe and exhaust as you suggested, placing the fan as close to the pipe as possible (pushing air is more efficient than pulling air), with the fan at the "fixer" end
• Start with 3/8" holes every 6" along the full length of the pipe and test draw with an incense stick (assuming you don't have a "smoke stick")
• Where you need more draw, increase holes to 1/2". If necessary, add holes

Don't forget to have a large enough filtered air intake. The pipe over the trays should be the only exhaust.

[cyrus]

Do your pipe and exhaust as you suggested, placing the fan as close to the pipe as possible (pushing air is more efficient than pulling air), with the fan at the "fixer" end

Good point. Didn't think of that. However that would mean I'd have to place the fan inside the room. I was hoping to put the fan entirely outside, to suck out the air, and minimize noise from behind the terra cotta block wall.. which will be a dusty sob to break through...

[Jim C.]

There are fume hoods that are slotted for table level exhaust, and flat, easy to fabricate one with Sintra board ( foamed PVC )
here is a pic as an example I found on the web - http://www.directindustry.com/prod/g...13-727059.html
Google for slot fume hood.
Localized extraction with flexible hose is cumbersome, you have to hang it somewhere and if you lift a print up to examine or drain, you'll bump into the hose.

[cyrus]

There are fume hoods that are slotted for table level exhaust, and flat, easy to fabricate one with Sintra board ( foamed PVC )
here is a pic as an example I found on the web - http://www.directindustry.com/prod/g...13-727059.html
Google for slot fume hood.
Localized extraction with flexible hose is cumbersome, you have to hang it somewhere and if you lift a print up to examine or drain, you'll bump into the hose.

but if you note, the samples on that page are localized extraction, including the slotted table-level one you linked to. The description states that it is intended to be attached to a flexible arm. Which of course is quite cool.

But I get your point -- indeed I could build something that sucks the air out from backsplash level. It could be a pvc pipe with holes or a narrow slit and hopefully I can get even draw. But the localized extraction thing is cool and may work better.

[Jim C.]

but if you note, the samples on that page are localized extraction, including the slotted table-level one you linked to. The description states that it is intended to be attached to a flexible arm. Which of course is quite cool.

But I get your point -- indeed I could build something that sucks the air out from backsplash level. It could be a pvc pipe with holes or a narrow slit and hopefully I can get even draw. But the localized extraction thing is cool and may work better.

Yes, the example that I pointed to is to be attached to a flexible arm, Lenser posted a pic exactly what I was getting at, but you got the point,
it doesn't have to be a tube, I don't know what the fixation is with tubes. With a flat plenum it can be the whole back splash of the sink
and you get more useful space.

I've worked with localized extraction with flex tubes, while not in a dark room situation, it can be a royal pain.

[cyrus]

Yes, the example that I pointed to is to be attached to a flexible arm, Lenser posted a pic exactly what I was getting at, but you got the point,
it doesn't have to be a tube, I don't know what the fixation is with tubes. With a flat plenum it can be the whole back splash of the sink
and you get more useful space.

I've worked with localized extraction with flex tubes, while not in a dark room situation, it can be a royal pain.

I guess pvc tubes are just more accessible but I could use 4" square plastic fence posts or smaller roof drains etc which are rectangular, and thus also form a little shelf..
.