I think that such a deep filter will eliminate the need for a screen. Would this be totally wrong? If so, is there a way to build the DIY flow hood to achieve a laminar flow using one of these inline centrifugal fans? It seems to me that so long as the plenum is air tight besides the entry point(fan location) and exit point(HEPA filter), the plenum will achieve a static pressure (based upon the cfm of air driven by the fan and the resistance of the HEPA filter) and flow smoothly out of the HEPA. The argument is that the air pushed by these fans is turbulent and so will exit the HEPA filter in a turbulent fashion. The main question is whether these inline fans will produce laminar flow. The build for a laminar flow hood using these inline fans look, generally, like the two samples at the bottom of this link ( ). Many people are interested in using inline centrifugal fans because they are cheaper than squirrel blowers, more quiet, more energy efficient, and potentially more compact. It is generally accepted that a squirrel blower is effective at creating this laminar flow using the set up in the image posted above. The cabinet cost $400 at a used office furniture place.Ĭompared to a couple thousand dollars plus $200 filters for a commercial fume extractor.So for years on the mycology, plant tissue culture, and DIY laboratory websites there has been this ongoing debate on how to achieve laminar flow in a home built laminar flow hood. but be aware that lots of harmful chemicals have no real odor. If using strong smelling resin, you should not be able to smell anything… This rig should easily clean the air of the trace fumes produced by the resins. The overall design runs with the doors to the cabinet closed… the cabinet is NOT airtight… there are gaps between he doors and the various panels of the cabinet that act as the plenum to draw room air INTO the cabinet from multiple areas- while the fan pulls the cabinet air thru the filter and out creating a negative air pressure inside the cabinet so that air only flows IN thru the various narrow gaps. The design passes the airflow thru the center of this thin filter- then again thru the rim of the filter as a final carbon filter stage to eliminate chemicals from the air. You buy them 6 or 12 at a time for about a buck each. On the outflow end of the fan you can see a part I designed and printed to act as a diffuser and to hold a final filter stage- a 6.25" wide carbon filter they make for garbage cans and composting bins. I had tried mounting the fan INSIDE the cabinet, on top of the filter- but I discovered that the EMI from the fan caused the Printer level bubble to go nuts… so I put it outside the cabinet. This is ducted to a 4" inline axial fan that is whisper quiet- and actually comes with a temperature sensor probe I mounted in the cabinet just to monitor the interior temp- since I also store tanks and cartridges of resin in the cabinet. These are sold online by outfits that supply indoor pot growers to keep the stank of their sinsemilla from giving them away- they run around $24 to $40 each… and should last a long time. Inside I mounted a shelf to hold a 4" port industrial activated carbon filter with a 1.5" thick carbon layer so the filter should last at least a year. I modeled and printed a flange with hose couplings and screwed that on top with a gasket. I bought a used grey steel cabinet with black shelves to help keep extraneous light to a minimum, And cut a 4" hole in the top. Those can be expensive if you buy them thru a commercially sold 'fume extractor" manufacturer… but you can build your own pretty affordably. What you need to clean the air of fumes is an activated charcoal or carbon filter. Moreover- where is the filter? At top or bottom of your drawing? Are you trying to clean the air around the printer? or the air you are breathing? The chemicals that the resins give off in small quantities will not be filtered out by HEPA- that’s just a filter small enough to trap very small particles- NOT chemical fumes.
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