DIY air filtration unit for <$200

[Dan Hintz]

As payback to the lasering community, I'm sharing my "plans" (such as they are) for everyone to copy. Well, not so much "plans" as pictures of the completed unit, but it should be obvious how to recreate something similar.

Due to poor planning on my part and a lack of any real sleep, I made one or two errors in the construction of this unit, but I'm happy to say it works like a dream. After a solid hour and a half of engraving a maple block at 100% power, there was only the faintest aroma of wood in the air, and not the tiniest touch of smoke haze. It all took a few weekends, each with a few hours here and there to allow for drying of the caulk, and the cost was under $200 :)

Materials:
1) Trashcan ($25)
2) 4" PVC piping, 2' ($6)
3) 3.5" PVC cap ($4)
4) 3/4" PVC piping, 2' ($2)
5) HEPA filter ($23)
6) Furnace filter ($10)
7) Silicone caulk ($3)
8) PVC cleaner/cement ($8)
9) Activated charcoal, 50 lbs. ($115)

Tools:
1) Caulk gun
2) Saw or Dremel

The great thing about this project is there is no real measuring to be done, just align things by eye or what "feels" right. The first pic is of the outside of the unit. It's nothing more than a typical plastic kitchen trashcan. Two 4" PVC tubes allow air in/out, with a ring of the 4" pipe chopped into short segments glued both inside and outside of the trashhcan to help act as a barrier to air (with the caulk) as well as give the joint more strength.

The second pic shows an inside shot so you can see a few 3/4" supports, roughly 6" in height, simply taped to the walls. These supports, along with friction from an over-size cut, hold up the furnace filter, just above the 4" inlet pipe.

This furnace filter, shown in the third pic, is sold as a cut-to-size sheet of a basic blue filter and a charcoal filter. The final filter sandwich consists of a plastic support mesh, blue scrubber, black charcoal, and another support mesh, all tied together with the included plastic ties. I cut it about 1/2" too large all around to give me a friction fit.

The final pic shows the whole shebang put together, minus the activated charcoal, with the HEPA filter installed. The HEPA filter was purchased at Sears as a replacement filter for one of their shop vacs, and the end was plugged using the PVC cap attached to the inside of a short length of the 4" piping.

Air from the machine comes into the bottom of the machine, the blower connects to the top. Use about a 3" layer of activated charcoal on top of the furnace filter... the edge supports and the friction fit will hold up that small amount without issue. Dirty, smoke-filled air comes in at the bottom, the furnace filter traps large particle, like scrap paper, etc., the charcoal above it traps the smoke particles and/or noxious plastic fumes, and the HEPA filter traps anything missed.

If possible, weigh the charcoal charge and the whole assembly as a separate item. Weigh the entire piece, charcoal and all, from time to time... when the weight of the charcoal roughly doubles, it's time to change it out.

I hope I didn't miss anything, but if I did I'm sure someone will ask...

[sal shepherd]

Great job Dan, And without any LED's. This build is alot better than what I have built and simpler.
Thank You

[Viktor Voroncov]

Thanks for advice, Dan. Where you buy HEPA for $23? Here in Lithuania price start from $90 :(

[Frank Corker]

Nice one Dan, I love it when people think inside the box!

[Mike Null]

Dan

Neat idea! Do you have any way to measure or judge the exhaust flow from the laser. There will be some flow restriction.

[Dan Hintz]

Viktor,

Sears is a major retail store here in the States, selling everything from clothes to appliances to tools (under the Craftsman brand name). Their shop vacuums use a handful of interchangeable filters from standard filtering to HEPA levels. Here's a link so you can see what I'm talking about, but I'm willing to bet you can find a place closer that sells a similar item:
http://www.sears.com/shc/s/p_10153_12605_SP100A5536S254315124P




Mike,

I have no way to judge actual flow (no in-line anemometer), but it's more than adequate. I'm using the red extractor from Harbor Freight with the variable speed controller unit for routers. At 100% speed, the blower is a complete noise racket... I turned it down to around 90% on the dial for a significant reduction in noise with no more than a very minor perceptible change in smoke removal. The smoke was heavy (I was burning 1/32" deep into maple at 100% power), but it practically hugged the substrate's surface as it was wicked out of the machine.

I wasn't sure how well this would work when I built it, but I'm extremely happy with the results. When other pre-built machines cost $4k+ plus several hundred dollar filter replacements, I use a sub-$100 extractor, <$100 in materials, and $115 for 50 lbs of charcoal that will last me for 10+ refills. I can even send the charcoal back to be recharged, though I haven't tried it yet, so I don't know what kind of discount it would net me... shipping cost alone (about $25) may make it unfeasible.

My main "mistake" was the direction of airflow. Initially, the design was to have the inlet up top, pass through the furnace filter, then charcoal, then a second furnace filter (used only to hold the charcoal up), and then the HEPA at the bottom before going out to the extractor. My thinking was the top-to-bottom airflow would compact the charcoal and ensure the best filtration of fumes, whereas a bottom-to-top airflow might float the lightweight charcoal and prevent any real filtration. After cutting the holes I realized it would be a PITA to get to the HEPA filter at the bottom, so I swapped direction, completely forgetting about my original line of thinking. I was nearly finished when I realized my goof, but I was so far along I couldn't change it back, so I decided to finish it up and at least give it a try. It doesn't appear to be an issue, but I would suggest looking for a convenient way to get a top-to-bottom airflow on the next iteration.

[Mike Null]

I doubt that bottom to top would be any sort of a problem with respect to the charcoal. Most of the range hoods in the kitchen which use charcoal work like that. They don't have an option but even so they do a respectable job given they don't have the advantage of a hepa filter.

[Dan Hintz]

They also only have to get rid of some burnt chicken smell, not noxious acrylic vapor that would eventually eat away your lung cells ;) I wanted this system to get rid of everything, not just reduce the smell a bit. Since I recirculate the air back into the room (and my health is always in question ;) ), I wanted there to be no question.

I was a bit nervous doing this last project because it was such a long burn and the filtration system hadn't been tested yet... I half expected the room to be filled with smoke in two minutes, but the only way I could tell wood was burning was when the top was opened.




Oh, I should also add... the pictures don't show the trashcan's lid, but it's there, and the open edges are covered in tape to make sure all air comes through the laser.

[Randy Digby]

Great design Dan, and thanks for sharing. My design is a little different but the one thing I have learned that might help in any design is that I now use cheese cloth to surround the charcoal. It does not restrict air passage and makes removal/exchange of the charcoal much easier, at least with my design.

The pics sure help - thanks for taking the time to show and tell.

[Dan Hintz]

I now use cheese cloth to surround the charcoal. It does not restrict air passage and makes removal/exchange of the charcoal much easier...
I'll add it in during my next charcoal swap... I just need to lay down one layer and leave the edges long. Come time to swap, gather the edges and pull the whole package out.

[Randy Digby]

That's exactly what I do. Before the cheese cloth, I had to carry the scrubber down to the garage to change charcoal because of the dust. I leave the ends long, like you say, and simply gather the sides together and lift the charcoal charge out and replace in the same manner.

[Dan Hintz]

Now to FIND some cheese cloth... <opening up Google.. tap tap tap...>

[Mike Chance in Iowa]

Now to FIND some cheese cloth... <opening up Google.. tap tap tap...>

Grocery store. Baking aisle.

[Niklas Bjornestal]

Why not put the HEPA filter before the active coal? The main function of the active coal is to remove chemicals from the air and not particles, so it might be better to filter out as much particles as possible before the coal.

[andrew zen]

Great idea!! Where did you get the bulk activated charcoal? From an aquarium store?

[Dan Hintz]

General Carbon... there are a few useful selections, but I got the 55 lb bag of their C-30. The bag was $96 with $19 ground shipping.

[Randy Digby]

Reference the HEPA prior to the charcoal, in my experience, the charcoal actually filters out some solid matter that makes it through the furnace filter pre-filter which presents cleaner air to the HEPA filter. This, I think, greatly extends the life of the HEPA filter, which is the most expensive item in the assembly. Others may have different experiences.

I actually removed my HEPA filter from my system and started venting back outside to save the cost of the HEPA filter replacement. The main purpose of my scrubber is to remove the smell since I live in a close residential neighborhood. But then again my HEPA filter was 12" x 24" x 12" and ran close to $400.00 each.

I like Dan's set-up. I built mine out of 1/2" MDF. His is much easier to construct.

[Mike Null]

Your point is a good one. In my previous life we used metal mesh filters ahead of the charcoal to protect the charcoal filter from solid particulates thereby extending the life.

I have a hepa filter on my vac but don't know if it has odor reducing qualities like charcoal.

[andrew zen]

Apparently our friends who are into growing ganja, have this filtering all figured out so that people don't smell their growing plants.

http://www.hydrofarm.com
http://www.rollitup.org/indoor-growing/7074-easy-build-diy-carbon-filter.html

Search eBAY for "carbon filters" or "Carbon air scrubber"

There are a lot of DIY projects on the web using ductwork/ aluminum fencing and carbon fernace filters. But I think Dan has a good way.

[Steven Wallace]

Dan what was your source of the charcoal?

[Dan Hintz]

Steven,

See post #16 above...

[Steven Wallace]

Thanks Dan I am afraid I posted my request before I looked through the other prior posts that were added after I first read your post.

[Sandy Henry]

Ok Dan, I think I'm in love...can't wait to try this. Thanks for sharing. Sandy

[Sandy Henry]

Any favorites for the activated charcoal filter material suppliers? Thanks, Sandy

[Dan Hintz]

Just look for the cut-it-yourself filters at Home Depot, Lowes, etc. One filter is blue, the other black, and there's a black plastic mesh and clips with it.

[Sandy Henry]

Hi Dan, How much charcoal did you use? Is it granular or pellet?
Thanks, Sandy

[Dan Hintz]

4mm pellets, if memory serves... the ordering info is in post #16...

[Sandy Henry]

Dan, I'm not too swift at getting around this forum! Sorry I had missed post #16.
I've got it now...Thank you very much. Sandy

[Frank Defert]

Dan I know you tested your scrubber with wood, but have you used it with plastics. I do alot of Rowmark tags and a little acrylic and was wondering how it does with those products?
I am going to build one just trying to figure out if i need to go larger for plastic? or is it good as is.
Thanks for sharing a great project.
Frank

[Dan Hintz]

If I can't smell wood at all, it means it is really taking the noxious fumes out of the air. Plastic would be no different.

[Mike Chance in Iowa]

Dan I know you tested your scrubber with wood, but have you used it with plastics. I do alot of Rowmark tags and a little acrylic and was wondering how it does with those products?



If I can't smell wood at all, it means it is really taking the noxious fumes out of the air. Plastic would be no different.

So in answer to Frank's question, you are saying you have not tested it with plastics?

I couldn't smell wood at all with my indoor filtration system I used to use before I moved, but there have been times when I could smell plastics.

[Dan Hintz]

I have not run it continuously for 1.5 hours with plastic like the plaque, but I have done short bursts... the only time I can smell it is when I lift the lid (make sure your entire exhaust is free from cracks, though it shouldn't matter in this case as the DC is after the filter).

[Randy Digby]

My scrubber is very similar to Dan's and I run a fair amount of plastic (over 1,000 labels a month) and my scrubber handles the odor without any problem. We vent outside and about once a week I'll go out and check the output for odor since we have close neighbors. I'll often engrave and vector cut a 12" x 24" sheet into 60 to 100 small labels with no exhaust odor at all.

In my case, the "tuning" part of building my scrubber was finding the correct thickness of charcoal. To little and the odor passes through and too much and the air flow is too restricted.

I like the simplicity of Dan's design vs. my box built of MDF, but both will work well with the right combinations of filter, charcoal, piping and air flow.

[Frank Defert]

Thanks Dan, and Randy thanks for your plastic info, just what I wanted to know.

Frank

[Leon Shreves]

Dan,

Great design. I saw on a more current and comical thread that you were thinking of upgrading to a 2 HP blower. Care to share your experiences on this? Would it be quieter if throttled back?

Regards,
Leon

[Dan Hintz]

Leon,

I'm awaiting a coupon in the mail before ordering... since I don't yet have the Stinger in house, it's no pressing matter. The coupon is only for $10, but as I'm in no immediate need for the item, $10 is $10.

I'm looking at the PSI DC2000B, and it's rated at 65dB... compared to the banshee-scaring HF red unit I'm using now, that's the equivalent of a mouse passing gas. $10 off coupon plus a $10 online code, I hope to get the unit for $320 shipped and add on a Wynn nano filter for another $150. The laser will still pull through the design laid out in this thread, including the HEPA inside of it, but I may gate this circuit down some to prevent too much pull. The other circuit will go to the Stinger, and I'll have to decide how I want to branch one of the circuits if I ever get around to adding on a good bandsaw.

[John Noell]

Thanks for advice, Dan. Where you buy HEPA for $23? Here in Lithuania price start from $90 :(
At least you CAN get one there Viktor. Not here. That's $23 plus about $100 shipping plus 32% duty plus 12.5% VAT or about $180 total. I'd be happy with $90.

[Leon Shreves]

Dan,

I take it that the HF 2 horsepower dust collector shown here:
http://www.harborfreight.com/garage-shop/stationary-dust-collectors/2-hp-industrial-5-micron-dust-collector-97869.html

Isn't the one you were referring to. Do you have a link to the one your interested in?

Thanks in advance,
Leon

[Dan Hintz]

Leon,

This is the one I currently have from Barbarous Freight:
http://www.harborfreight.com/1-hp-mini-dust-collector-94029.html
http://www.harborfreight.com/media/catalog/product/cache/1/image/370x/9df78eab33525d08d6e5fb8d27136e95/i/m/image_2847.jpg

And this is what I'm ordering soon from Penn state and adding on a Wynn HEPA (looks like I screwed up the number a few posts back... I'll edit it now):
http://www.pennstateind.com/store/DC2000B.html
http://www.pennstateind.com/graphics/275px/DC2000B.jpg

[Dan Hintz]

Interesting... I just saw this muffler:
http://www.pennstateind.com/store/SUP1000.html
http://www.pennstateind.com/graphics/275px/SUP1000.jpg

I'll see how quiet this thing is first before ordering the muffler, but I wouldn't mind making it as quiet as possible...

[Leon Shreves]

Thanks for the info Dan. I noticed that they sell the 1.5 HP motor separately for under 300 bucks. It is as quiet as the 2 hp unit. That might be attractive too if the only use was to support the laser engraver.

Regards,
Leon

[Kasey Maxwell]

Dan, I have this blower http://bit.ly/cTEIaK will the filter you made work with it ? I don't know if it's to powerful or just right :)

Thanks

[Dan Hintz]

Ouch... $308+S/H for a 3/4 HP DC?

Anyway, you will probably be okay if you keep your run short, but I definitely wouldn't go any lower in power. The DC I'm running on now from HF is 1 HP... it pulls plenty of air through with decent suction capability on the vector table, but it won't suck a golf ball through a garden hose.

You really have nothing to lose by trying it out.

[Kasey Maxwell]

yea they have gone way up in price, I got mine for like $250.00, it works good, very powerful, I just don't want to blow the trash can apart ! :D

[Ron Hartl]

Great job Dan! Much appreciated!

[Kasey Maxwell]

After seeing your blower, I think I'm going to sell mine and get one of those, this one is good but may as well get full power !

[Robert Walters]

Hi Dan,

Nice idea on the air scrubber, I'm going to have to plagiarize and see what works out =)

As I'm still setting up things here...
Could you tell me WHERE the sound on the HF DC is coming from the most? The motor? the blades? intake shroud? exhaust shroud?


The reason I ask is that I'm actually thinking of combing both the air scrubber and a sound proof enclosure into a single unit with the DC motor sticking out if it's not the main noise source.

Since HF doesn't list the dBa nor the Static Pressure, I have no idea how much benefit I'll gain from using the speed control to reduce it down.

I'd much rather spend money on equipment as a substantial savings to electrical power and noise pollution.

The 6" inline fans from the hydroponics stores are 450CFM (@ 0" SP), 50 dBa, less than an 1 amp, but only have like 1" SP @ 250 CFM

http://atmosphere.com/english/html/product/fans/vtx/vtx600.html

I'm still searching for that happy medium between the two.


In case I missed it...
What activated charcoal did you get and where from?
Links are always appreciated =)


Did you notice the power requirements of the DC you're looking at?
9A @ 220V or roughly 18A @110VAC

[Dan Hintz]

The majority of noise usually comes from the impeller, as that's what is chopping the air. The sound form it escape mostly through the exit pipe, so that's what you want to muffle if you only get to choose one thing. That said, you'll get a much larger reduction in noise by soundproofing the entire DC. According to the manual, the HF 1HP unit is rated at 107-112dB @ 3 feet. It is not a quiet machine by any stretch of the imagination. I only used the speed control to dial down the noise level, and it helps significantly, even at 90%. The HF unit is listed at 914 CFM (most likely at 0" SP), and I'm sure it drops off pretty quickly. Your units lists half that at twice the intake area... that would concern me greatly. I don't think that hydroponics unit is going to do much for you other than offer a gentle breeze in the cabinet, and I doubt it would offer any vacuum capability to speak of.

I'm running it on a dedicated 20A circuit (well, the circuit does run a couple of shop lights), so I should be okay with the new unit.

Info on the carbon can be found around page 2...

[Joe De Medeiros]

Hi Dan,

Nice idea on the air scrubber, I'm going to have to plagiarize and see what works out =)

As I'm still setting up things here...
Could you tell me WHERE the sound on the HF DC is coming from the most? The motor? the blades? intake shroud? exhaust shroud?


The reason I ask is that I'm actually thinking of combing both the air scrubber and a sound proof enclosure into a single unit with the DC motor sticking out if it's not the main noise source.

Since HF doesn't list the dBa nor the Static Pressure, I have no idea how much benefit I'll gain from using the speed control to reduce it down.

I'd much rather spend money on equipment as a substantial savings to electrical power and noise pollution.

The 6" inline fans from the hydroponics stores are 450CFM (@ 0" SP), 50 dBa, less than an 1 amp, but only have like 1" SP @ 250 CFM

http://atmosphere.com/english/html/product/fans/vtx/vtx600.html

I'm still searching for that happy medium between the two.


In case I missed it...
What activated charcoal did you get and where from?
Links are always appreciated =)


Did you notice the power requirements of the DC you're looking at?
9A @ 220V or roughly 18A @110VAC

these fans have a lower max static pressure (around 2.5" wc), and don't work nearly as well as the dust collector blowers, they are more sensitive to duct size than the DC blowers which are more a brute force fan and typically have a max sp 6" wc or higher. They are more suited for short runs around 6 feet, and suffer greatly when combined with flexible duct.

[Robert Walters]

these fans are more suited for short runs around 6 feet, and suffer greatly when combined with flexible duct.

Hi Joe,

Yeah, I'm aware of the much lower SP, I've been reading datasheets like crazy.

I guess I'm just trying to find a happy medium between an inline fan and a DC, especially since I won't be collecting chips (gawd I hope not =).

I'd much rather spend the money on equipment, than to just waste it on electricity and ear plugs.

If a DC draws 8Amps, and a inline fan draws less than 1Amp, with enough research I'm sure there's an alternative out there drawing 4-5Amps and less than 50dBa.

Since I have your attention and you mentioned you used to design HVAC systems:

For my own curiosity of "Air flow 101"...

If I went from 4" duct to *TWO* of those 6" inline fans (at 2" SP@ 250CFM each), what would I get as the result of them in SERIES?
I understand it's not linear, but what it is I don't know.

[Laser 4" duct] --> [6ft of 4" flex duct] --> [4" to 6" adapter on 1st inline fan] --> [2nd Inline fan] -->[25ft of 6" flex duct]

I don't plan on using this setup, but I'm trying to get a better understanding of the technical aspects.

[Joe De Medeiros]

Robert, if you make the 4" section smaller say 12" the loss in this section is .14"wc, and make the other section 25ft @ 6" the loss will be .762" that's .777"wc total loss, from the fan chart that's 297cfm (one fan), now Dan's filter will add another restriction, I'm not sure how much, but if you were to add a 2nd fan on the outlet side, it will act as a booster, both fans have to be the same or you will get a fan in-balance. Your other alternative is to go with an 8" fan (vtx800 747cfm) and 8" duct (smooth wall), it will give you about (.66"wc loss) 540cfm less whatever Dan's filter takes away. The vortex fan sound like a jet engine, I have 10" ones I use when I'm welding, I'm not sure how many DB's they are.

The 2 fan solution will work as long as they are far enough apart to not conflict with each other, it will give you close to the rated CFM as one fan.

[Laser 4" duct] --> [12" of 4" flex duct] --> [4" to 6" adapter on 1st inline fan] -->[25ft of 6" flex duct] -->[Dan's filter]--> [2nd Inline fan] this works by dividing the loss between both fans.

I hope this helps

[Robert Walters]

Joe,

Thanks for the info, I'll have to let it absorb a bit =)



Dan,

Do you think that 50 lbs of activated charcoal would fit inside a 5 gallon plastic paint bucket with the lid attached?

[Dan Hintz]

I would say 30-35 pounds of it would fit without a problem... more like 1.5 buckets for the full 50 pounds.

[Kasey Maxwell]

I'm having great difficulty locating 50#'s of activated charcoal, can you specify where to get it from ?

Thanks

[Robert Walters]

I'm having great difficulty locating 50#'s of activated charcoal, can you specify where to get it from ?

Thanks


http://www.generalcarbon.com/vapor02.htm

(I had the page open already =)

[Dan Hintz]

I'm having great difficulty locating 50#'s of activated charcoal, can you specify where to get it from ?

Thanks
All pertinent info has been posted in this thread (wish I could edit the original post).

[Joe De Medeiros]

I'm having great difficulty locating 50#'s of activated charcoal, can you specify where to get it from ?

Thanks

Have you tried local hydroponics stores, they seem to carry it for air scrubbers, but I live in the pot capital of Canada it seems (largest pot bust in Canadian history)

[Kasey Maxwell]

so far only one out of like 20 hydroponics stores i called carry a 16# bag of activated charcoal and they want $85.00 for it :eek: !

I will keep searching..........

[Robert Walters]

Kasey,

http://www.generalcarbon.com/vapor02.htm
$95.70 for a 55 pound bag + roughly $60 for shipping to California.
as of when I called them today.

Even with shipping, still MUCH cheaper that I can find it locally.
One local aquarium store quoted me ~$500 for 50 lbs.

If you don't need 55lbs, maybe you can find someone locally to split with.

[Robert Walters]

Looky what I found....
http://www.harborfreight.com/8-inch-portable-ventilator-97762.html

It has the CFM, not sure on the SP. Wonder if it'll work.

[Dan Hintz]

At 1.4A, that thing would probably drop to 0 CFM at even a hint of moisture in the air...

[Robert Walters]

At 1.4A, that thing would probably drop to 0 CFM at even a hint of moisture in the air...


They use those for when people go into sewer manholes.

Were you talking high humidity or something?
I'm not planning on lasering watermelons here =)

[Richard Rumancik]

Robert, I'm not sure what Dan meant but in any event the item you have identified is intended to be used as a fan, not a blower. By that I mean it was not designed to be used against any sort of impedance (restriction). You can't add ducting to a fan and make it into a blower. The reason why they don't specify static pressure is because it will generate the specified flows only at 0" water (no restrictions on intake or exhaust ports). As soon as you add any restriction on either end, the flow will go way down drastically.

Sometimes the terms fan and blower are used interchangeably but the unit you show is clearly meant to move a high volume of air with very minimal backpressure. For laser systems you need a unit that can generate around 6" of static pressure with a flow usually in the neighbourhood of 400-800 cfm - but it depends on the laser manufacturer's specs.

[Robert Walters]

Richard,

There's actually a duct that goes with that:
http://www.harborfreight.com/8-inch-ventilation-duct-97763.html

Though they do say that for each 90 bend, the CFM drops.



I'm STILL looking for that happy medium without the amperage and noise pollution, but looks likes I'm going to buy Dan's Red beast tomorrow:

http://www.harborfreight.com/1-hp-mini-dust-collector-94029.html

as I can at least speed control it a bit, where as the green one:

http://www.harborfreight.com/13-gallon-industrial-portable-dust-collector-31810.html

as I understand it can NOT be speed controlled.

[Richard Rumancik]

Yes, I suppose that if you want to vent a manhole you could attach a piece of large diameter duct to the intake, position it into the manhole, and hope for the best. But the unit is really not suitable for integration into a laser system.

[Dan Hintz]

At 1.4A, that thing would probably drop to 0 CFM at even a hint of moisture in the air...
Let me rephrase that...

At 1.4A, that thing would probably drop to 0 CFM at 0.000000001" of water...

There's a huge difference between high CFM at 0" of water and even low CFM at 4-6" of water. It might give a mighty breeze when set in the open, but hook it to a laser and expect it to pull any pressure and you can expect it to do little more than make some noise.

[Robert Walters]

At 1.4A, that thing would probably drop to 0 CFM at 0.000000001" of water...

Ah, gotcha.


I found the "PERFECT" exhaust system... NOT!
http://www.sears.com/shc/s/p_10153_12605_00921393000P?prdNo=16

But good for a laugh anyway!


Wouldn't you know it...
HF (retail store) is OUT-OF-STOCK of your demon dust collector today!
Maybe that's telling me something, I just can't win it seems.

[Robert Walters]

Dan,

I bit the bullet and got the Harbor Freight red DC.

I was surprised as it's really not as loud as I thought it would be,
for an office it be loud, for a shop fairly quiet (subjective I suppose).


In your air scrubber...

What were your goals in the use of the filters?
Both HVAC and the ShopVac HEPA?

Since you are recirculating air in the room, I suspect that's why the HEPA filter, but the HVAC filter I'm note sure about, unless you have the air scrubber for a dual purpose as I would think a laser isn't going to have much more than the occasional scrap of paper/particle once in a great while and aluminum screen could resolve that. Over engineering???

And if you have some better pics of the HVAC ones and how it's used inline, that would be appreciated.

How much activated charcoal "dust" have you accumulated on the the bottom of the pile? Is it enough that it needs to be filtered to prevent escaping out? Is it actual dust (like baking flour) or like grains of salt/sand?

When/if the "dust" builds up, does it have a significant effect on the throughput?

Sorry for all the questions, I'm working on an idea I have and just trying to figure out if it's "good enough" or if I'm over-engineering the thing and I'd rather learn from other's experiences instead of reinventing the wheel.

[Dan Hintz]

Robert,

The HVAC filters are there mostly to catch the "big" stuff and prevent it from contaminating the charcoal pellets, as well as allowing the air a large surface area to pass through for the charcoal. It also acts as a nice tray to hold the pellets. The pellets are about 4mm in size.

[Robert Walters]

Robert,

The HVAC filters are there mostly to catch the "big" stuff and prevent it from contaminating the charcoal pellets, as well as allowing the air a large surface area to pass through for the charcoal. It also acts as a nice tray to hold the pellets. The pellets are about 4mm in size.

What about carbon dust?

I would suspect that after some prolonged use, there would be a build up of activated carbon dust on at the bottom of the pellets.

I was just wondering if this is minimal (<1/4") or significant (1" or more) between change outs?

[Dan Hintz]

I ran it for a few seconds without the filter, then I ran it for a few minutes with, removed filter, tapped it clean, then ran as normal.

[Shawn Cavaretta]

thanks for posting this info. over the weekend i built a unit it is a wood box 12w 20d 24 h.

i have about 2 1/2 in of carbon in there now and i still have a slight odor when cutting wood and acrylic. im thinking about adding another inch tomorrow and seeing of that works. what do you think

[Mike Null]

Keep in mind that the unit can be working as designed and residual odor may remain in the room from the items you have cut.

[Shawn Cavaretta]

i added an extra 1 1/2 of carbon for a total of 4 inches and i am getting no smell

i will post a drawing of my set up later this week

[Gary Liberman]

Hello, as you know we are about to receive our new ULS 4.60 system, and I would like to know if its mandatory, or better for the system to install an air filtration unit?

Thank you!

[Dan Hintz]

Gary,

It makes no difference to the system if you scrub your exhaust... it only matters to your lungs if you exhaust inside.

[Leon Shreves]

Hi all,

General Carbon provides their carbon to aquarium owners in smaller quantities at this URL:
http://shop.happyfishcarbon.com/main.sc

I was assured by a General Carbon sales person that carbon is the same as that used by Dan.

I got two gallons shipped to me for $48. A gallon does a 3" layer in my instance of Dan's design. Shipping is a hefty $19 regardless of amount.

I fired up my scrubber yesterday and I was still getting some odor out of the exhaust. I need to tweak my implementation a bit. One thing I did wrong was wrap the filter material up the walls of the scrubber for a couple of inches. That is probably allowing fumes to skirt around the carbon.

I did some other changes to the design, too. I attached the filter support to the walls with tie wraps going through holes I drilled in the walls. I did this because PVC didn't want to stick to the plastic walls. I covered the holes and tie wrap stubs with a strip of duct tape. Ugly but air tight. Also I am not using the HEPA filter currently since I am running my exhaust outdoors. The smell going outside is hardly detectable. I have tried it with Acrylic and mdf and I can smell the wood smoke from MDF fairly distinctly, to the point that I wouldn't want it going inside my shop.

I'll fix the filter material configuration and tune the amount of carbon I am using and I am sure it will work great.

With the smaller outlay for carbon and not using the hepa filter I was able to get a working prototype for around $100.

Thanks again Dan for the cool design.

- Leon

[Dan Hintz]

Ouch on that pricing... 2 gallons is what, about 5 or 6 pounds? For twice the price I got 50 pounds... anything more than very slow hobby will go through that 2 gallons in a heartbeat as that's about a single charge.

[Scott Woodson]

Darn!!! I wish I would have seen this thread before spending $1500 on a filtration unit that only filtered for about an hour, filters alone cost more than you entire set-up. Going to see about using this as a pre-filter for my unit to see what happens. I may also see about packing more charcoal into the unit I have. Thanks Dave for sharing.

[Bob D.]

Was NASA your inspiration on this filter build? You didn't by chance
just finish watching Apollo 13 before you put your filter together did you?

In all seriousness nice job.

http://www.youtube.com/watch?v=Z3csfLkMJT4&NR=1

[Robert Walters]

FWIW...

27 lbs of 4mm pellets == 1 cubic foot.

[Robert Walters]

Was NASA your inspiration on this filter build? You didn't by chance
just finish watching Apollo 13 before you put your filter together did you?

In all seriousness nice job.

http://www.youtube.com/watch?v=Z3csfLkMJT4&NR=1


Bob++

Classic!

Bonus Karma for that!!!!!

[Dillyn Benjamin]

Greetings all

I'm new here and have been reading many of the various posts and can only say wow what a vibrant community. It has taken me quite a while to find it.

I have a question regarding this really neat filtration unit design. I'm thinking of building one to use for filtering mostly rubber and romark fumes on a Legend Ext 75. The sytem that I am using now is rather large and clunky and I'm hoping that I can switch to this design which is very keen!

Has anyone tried this with rubber?

Thanks
Regards
Dillyn

[Dan Hintz]

I'm not a fan of rubber (of any type) in the laser, but I did it once to test the unit. The only real smell I noticed was once I stopped the air and lifted the lid (no matter what I cut, there's a always a faint odor in the air). the carbon layer does na excellent job of keeping the exhaust clean of noxious fumes.

[Dillyn Benjamin]

Hi Dan,

Thanks for the prompt reply, I appreciate the help. My apologies for the tardiness of my response it's been a rather busy time lately. I don't have a lot of choice about rubber in the laser as I make rubber stamps. I'm going to be assembling a slightly larger garbage can version of your filter design. I'll let you know how it works out.

Thanks again
Dillyn

[carlos alencar]

Should i wash the charcoal before put it in the trash can ? i got a beautiful black powder.......

[Dan Hintz]

Wet charcoal won't capture anything...

[carlos alencar]

how to eliminate the black powder ? leave it on for a whole day ? or did i bought the wrong activatec charcoal ?

[Robert Walters]

how to eliminate the black powder ? leave it on for a whole day ? or did i bought the wrong activatec charcoal ?

Just rinse out the pellets using water and let fully dry before using.

Wet activated carbon depletes oxygen, so do this outdoors.

[Dan Hintz]

I just run the machine for a few minutes, take out the HEPA filter and bang it on the ground for a minute or so... repeat, if necessary. I'm not a fan of washing as any chlorine in the water (along with many other chemicals) will reduce the effectiveness of the charcoal. After all, activated charcoal is what they use (among other things) to make water filters, with the primary element removal being chlorine.

[carlos alencar]

thanks... i will try this again.

[Russell Ludwick]

Thanks for the plans Dan
I read through the thread and I didn't see any pictures of your activated carbon sandwich, I was wondering if you have one or if i just missed it.

I also had the idea of possibly adding in a water filtration stage before it enters the dry scrubber unit. Would there be enough sucktion to allow for something like that? or is that simply a bad idea?

Once the air comes out of the blower, do you just exhaust it to the outside as normal?

Again thanks for the design. I need this for my shop because I am tired of breathing smoke :)

[Dan Hintz]

No more pics than what's there... I figured the design was simple enough that people can use their imagination and make their own tweaks.

I don't see much need in water filtration, and in fact it could "harm" the process by filling the carbon with moisture, preventing it from sucking up the fumes. Between the furnace filter trapping particles big enough to pick up with your fingers (dust, dirt, etc.), the carbon removing the noxious fumes, and the HEPA filter removing anything that's left, it does an amazing job of keeping things clean. Other than a very faint smell of the material, the only smell I really notice is when I raise the top between jobs. I exhaust right next to my machine back into the room... if I was exhausting outside, I wouldn't bother scrubbing it.

[Rich Harman]

I am trying to decide upon either venting outside or making a carbon scrubber. Each has it's advantages. Not the least of which is that if I vent outside I have to alter the venting for the gas water heater.

Dan, have you had to change out the carbon yet? Most of what I do is cutting, I am concerned that the charcoal may not last very long.

[Dan Hintz]

Yeah, I've changed it since then... how often will depend upon how much junk you force through it (i.e., how much work you do). Still, at <$100 per 50 pound box and being able to get around 10 charges per box, that's actually a lot of work. For a really busy shop, that will probably last you 6 months... for lesser shops more than a year.

[Khalid Nazim]

If I understand this correctly, this unit would allow me to extract air in that same area as my machine instead of extracting outside? I am trying/planning to make this arrangement instead of making a hole in my basement wall and extracting outside.

I am having a bit of brain freeze here and hence my question :(

[john banks]

I wondered how a vacuum cleaner might work?

http://www.numatic.co.uk/products4.aspx?id=1&r=4&sr=1

We have one like this for the house. It flows 42 liters (this is on the high setting which is a little noisy, presumably 21 liters on low) per second and has cheap HEPA bags. If I filled the area around the bag with activated charcoal could it work?

The 600W motor (when running at low setting) is just a bit more powerful than the 550W upgraded exhaust fan you can get from Shenhui (standard 330W I believe).

There is also a "Harry" model which also contains a large volume charcoal filter. Trying to find pictures of it and see how big it is...

[Dan Hintz]

I wondered how a vacuum cleaner might work?

http://www.numatic.co.uk/products4.aspx?id=1&r=4&sr=1

We have one like this for the house. It flows 42 liters (this is on the high setting which is a little noisy, presumably 21 liters on low) per second and has cheap HEPA bags. If I filled the area around the bag with activated charcoal could it work?

That's a mere 90/45 CFM (high/low)... not enough to suck up dust except at close range. The PSI DC is closer to 1,200 CFM at 6" of water.

[Khalid Nazim]

I finally made a filter unit based on Dan's design and its working good. The smoke is all gone but there is slight hint of smell sometime. I have to figure out if there are leaks. So Dan thank you very much for sharing your design. It is simple, elegant, practical, cost effective and effective.

I have to now deal with the fan noise issue. I bought a 1HP dust collector from Princess Autos http://www.princessauto.com/workshop/power-tools/stationary/dust-collectors/8353229-1-hp-mini-dust-collector and its too much noise to handle on a constant basis. Is there a fan that I can put outside my house which can handle the Canadian winters?

Regards

[Dan Hintz]

I have a tiny hint of the smell, as well, during processing of materials... the smell of wood is nice, and with the filter, never overpowering. I get a whiff when I open the lid to the laser, too. But the good news is the toxins in the smoke are now stored i the carbon, not your lungs.

[john banks]

Is the exhaust hose supplied with most machines 4"? Have all the bits now except the inlet to the HEPA filter is 2.5" so I will need to taper down briefly into this, but it is only over a short distance so shouldn't be a significant restriction I think.

Does anyone have an opinion on whether the supplied 550W exhaust fan with the machine will be enough to push or pull through this filter?

[Dan Hintz]

Is the exhaust hose supplied with most machines 4"? Have all the bits now except the inlet to the HEPA filter is 2.5" so I will need to taper down briefly into this, but it is only over a short distance so shouldn't be a significant restriction I think.

Does anyone have an opinion on whether the supplied 550W exhaust fan with the machine will be enough to push or pull through this filter?
Tapering to 2.5", for even a millimeter, is a huge restricton... find another HEPA filter with a proper inlet size, such as the one I suggested originally.

[john banks]

I'll try to keep it 4" with a few modifications. Parts that are routinely available in some places are difficult to find in others, finding activated charcoal at a good price in the UK was tough, but eventually Coastal Koi had 25kg (55lb) bags for £57 (about $89) and it arrived promptly.

My setup is hoover cylinder base, HEPA filter, cotton filter bowl that will take about 12" diameter and up to 4" depth of charcoal, charcoal panel filter (to stop it all going up the outlet!) and then a 12" (brewing) funnel that will be clamped, and cut off where it reduces to 4". I'll subject the forum to some dodgy photos for hilarity purposes only once built ;) Unless it goes horribly wrong and then I'll just keep quiet :)

Does anyone know if the Shenhui machines come with metal exhaust tubing or is it plastic?

[Khalid Nazim]

Shenhuis come with 8" rubber/PVC kind of tubing which has smooth inside walls. The exhaust opening at the back is also 8". I had to use a reducer to get it to 4" and then connect to my filter. Although the filter design is really simple and it works, I still need to take the exhaust fan outside as its too noisy to be kept inside.

[john banks]

Thanks. Is it the noise of the fan motor or the airflow inside the building that is noisy do you think?

[Khalid Nazim]

The fan motor is noisy.

[john banks]

We bought a 2HP dust collector, used once, from Ebay for £182 delivered.

The cotton filter insert was about £10, the HEPA filter bags are about 50p each, the black cooker hood filter was a few pounds.

Charcoal was £57 for 25kg.

Youtube comedy video youtube.com/watch?v=1sLEHonDQxY , wife and I have never made one together before, she has a habit of turning sideways/upside down, sorry :)

Don't have the laser machine yet so don't know how effective it will be.

Thanks Dan.

[john banks]

I do notice some restriction to the inlet flow (just feeling the suction) at the dust collector when the 4" thick (12" diameter) charcoal is added, and the pressure from the restriction would blow the lot upwards unless the filter over it was not held down well. Our charcoal is 2mm pellets, which may well add restriction but gain surface area. When we get the machine we'll play with less thickness if no smells are evident.

Anyone else notice much restriction when blowing or pulling through a bed of charcoal?

[Randy Digby]

There is going to be flow loss when the restriction of the charcoal is added, unless you have a very large blower system. My system has a small blower for noise consideration since it has to be located in the laser room. In fact, it is under the laser table. For this reason, I had to do exactly what you are referring to - I experimented with different charcoal layer thicknesses to arrive at the best level for my needs. I have a 12" x 24" bed of charcoal and arrived at 2-1/2" thickness of charcoal as the best fit for my blower flow and engraving process. I actually pull air through my filter from top to bottom so I don't get any "bubbling" of the charcoal. We all have a little different setup, which is fine, as long as it meets our individual requirements. Good luck wiht yours.

[Dan Hintz]

I would suggest going for a wider, but thinner, charcoal bed... I believe mine is about 2" thick, and maybe 12"x16".

[john banks]

Thanks. Latest method is using a stainless garden sieve (14.5" diameter, not much more than 12", but 46% greater cross sectional area and 86% of the cross sectional area of your estimated 12"x16" rectangle) which has some nice inserts. I've used a single HEPA layer and then about 2.5" charcoal above that. The pressure behind it is enough to float the new "cylinder cartridge" assembly in the air (!) so I have siliconed it down. After that sets I will try it tonight. I found that unless the charcoal is well compressed then airflow finds weak spots and heaves it up before flowing through a gap it has made, or if there is nothing holding it down, the whole lot would heave out onto the floor! Chicken wire domes up too much, it needs to be a more ridid mesh, so the garden sieve with inserts is great. A line of silicon around the top reinforces it to ensure all the air has to go through compressed charcoal. I don't want to split anything to measure, but it would be nice to know the pressure drop across the charcoal/HEPA. It still feels like a lot of airflow to me though, with the rated CFM it should empty the machine in a second based on 24 cubic feet estimate (for 1200x800mm machine), but obviously with ducting and the restriction and the speed controller (if it works) it will be less (the 1490CFM doesn't show it at a pressure rating and I cannot find data on it), but hopefully more than enough.

[Rich Harman]

I noticed that you left one of the caps in place when testing the DC. Air flow will be greatly increased with it open. If you remove the cap and the airflow doesn't change, then you know that the charcoal bed is the limiting factor.

[john banks]

That is for attaching a second (dust creating) machine I believe, this is my first dust collector, but it is presumbly a fair standard feature? I was anticipating leaving it capped because I'm only connecting one laser machine initially, otherwise I'll be sucking up room air rather than machine air. If I get a router, I'd not plan to mix potentially firey laser exhaust with dust which could be ignited.

I wondered for those of you using DIY air filtration units whether you've noticed much movement of the charcoal in operation or do you have it quite firmly packed in position? I anticipate whether blowing or sucking that it would need holding in place pretty good from what I see here, although I'm using only 2mm charcoal which might jiggle more. However, seeing the whole cartidge levitate was quite amusing.

Any thoughts on how much the commercial (BOFA/Purex) etc, flow compared to this sort of setup? They seem quieter and sound as though they use less power, are they up to the job for cutting wood for the sort of power and size of machine most of us are talking about?

[Joe Hillmann]

Is there any way to test the air coming out of the charcoal filter to make sure that it is trapping all the stuff you don't want to be breathing in? Right now I am venting mine outside which in the winter gets pretty expensive and would love to filter the air and vent it inside I am just unsure of the safety of breathing in whatever the filters miss.

[Gary Hair]

Is there any way to test the air coming out of the charcoal filter to make sure that it is trapping all the stuff you don't want to be breathing in? Right now I am venting mine outside which in the winter gets pretty expensive and would love to filter the air and vent it inside I am just unsure of the safety of breathing in whatever the filters miss.

get yourself a parakeet...

Seriously though, I have thought the same thing myself, it's the main reason I haven't made one yet. I figure if Dan disappears from the forum then I'll start looking at the obits to find out how he died.

Gary

[john banks]

Here is the garden sieve from above and below (looking at HEPA)

Silicone around the base is not neat, but it is sealed and stays where it is supposed to. I put another bead around the underside which you may just be able to see on the second photo.

I didn't want to silicone the very top grid but it shouldn't take long to cut the bead to change the charcoal and then a minute to redo it afterwards. I'd try to leave the frame in for changes.

215558215559

[Rich Harman]

That is for attaching a second (dust creating) machine I believe, this is my first dust collector, but it is presumbly a fair standard feature? I was anticipating leaving it capped because I'm only connecting one laser machine initially, otherwise I'll be sucking up room air rather than machine air. If I get a router, I'd not plan to mix potentially firey laser exhaust with dust which could be ignited.


Your laser will have a 6" outlet and a 6" flexible hose. Your DC has a 6" inlet (when you take off the plastic wye). Go ahead and try it. While the DC is running pull that cap off. There is a huge difference. Try it with, and without the charcoal so that you can compare.

[john banks]

Thanks, I just measured and it is 5". Someone said the machine outlet was 8" so I bought an 8" to 4" reducer. Will see when it arrives!

The airflow feels really good.

[Rich Harman]

You're right, my DC is 5" too. The outlet from the laser and it's hose is 6".

[john banks]

Planning to tweak this a bit more. Have found 8" diameter, 8" length HEPA filter cones (pleated) that are in stock locally so will try to get some tomorrow. They may have both ends or just one end open, but appear to come with a cap. Just one of these will have three times the filter area of the existing setup. They appear cheap enough not to bother with a pre-filter. I need to work out a way to interface the top of the 8" cone to the 12" diameter I showed from underneath in post #116.

When you get a cone filter designed for a shop vac, does the direction of airflow matter for the HEPA filter to work properly? With my proposed setup, the air would flow from the outside of the cone(s) and then up the inside. This is effectively the same way as Dan has it.

[Rich Harman]

Here is my plan for a carbon filter, it will fit in the empty space behind the table inside the laser.

215705

[Dan Hintz]

They appear cheap enough not to bother with a pre-filter.
I would question any HEPA filter that's also very inexpensive... "cheap" may be the correct term as it may not be a true HEPA. If it is, it will clog almost instantly, reducing airflow. The pre-filter is always a good idea, especially if you have carbon dust flowing at it.

[Ric Taylor]

Dan,

Actually, washing the charcoal is a very good idea. Aquarium enthusiasts have done that for decades. The charcoal is taken out of the aquarium filter, washed thoroughly with clean water, laid out to dry (preferably in the sun, but not absolutely necessary), and then reused in the filter over and over. This re-activates the charcoal, and the charcole removes all of the amonia wastes from the water that are created by the fish.

When fresh charcoal is introduced into the aquarium, it is first rinsed off to remove the black dust.

Ric

[Randy Digby]

I agree with Dan. Originally I had a large HEPA filter (12" x 24" x 10" or 12" thick and very $$$), but I abandoned it because it dropped my air flow down to where I would need to increase blower size (I pull through filter and laser and exhaust through the blower to the outside). I was going to exhaust back inside (original reason for HEPA filter), but opted to exhaust outside and not increase blower size to keep the blower noise level down since my blower has to be inside. All that said, my system would require charcoal changing, or at least "stirring", much more often if not for my pre-filter. I use chep 12" x 24" HVAC filters and I'll change the pre-filter up to six or eight times for every charcoal change. My nose tells me when to do a pre-filter change and I stir and inspect the charcoal each time I change the pre-filter. I don't weight my charcoal charge as some do but do a visual on bed thickness incress and general visual contamination to determine when charcaol needs changing.

By the way, Dan, I have not checked, but this has to be the longest thread on Sawmil - Congratulations!

[Dan Hintz]

Dan,

Actually, washing the charcoal is a very good idea. Aquarium enthusiasts have done that for decades. The charcoal is taken out of the aquarium filter, washed thoroughly with clean water, laid out to dry (preferably in the sun, but not absolutely necessary), and then reused in the filter over and over. This re-activates the charcoal, and the charcole removes all of the amonia wastes from the water that are created by the fish.

When fresh charcoal is introduced into the aquarium, it is first rinsed off to remove the black dust.

Ric
You need to make sure you rinse with deionized water, otherwise you're just contaminating the charcoal as you rinse off the dust.

To clean used charcoal, it needs to be heated to release the contaminants, not just washed with clean water and set out to dry. That may work with ammonia from decaying fecal matter as the captured ammonia will redissolve back into the rinse water and be carried away when drained, but that's not the case with the majority of contaminants caught coming from the laser.

[john banks]

$48 retail, but reduced to clear at $8 each so I got 5 of them which was all they had left, the cheapest I could find the same filter elsewhere was $23, so hopefully just cheap to clear rather than because it is rubbish. The non-HEPA filter for the same vac was on the shelf next to it at $20.

They are about 8" diameter, 8" tall. The area where the pleats are joined to the ends looks done well. I was thinking of joining two end to end which will reduce restriction and make them need to be changed less often, but will also see if I can get a foam filter to wrap around them too.

The direction of airflow in the original machine they would have been used for, is outside to inside, which is the direction I will be using them.

[Stephen Hooper]

I know it is a little old but am glad I found this thread as I am just about to embark on the same exercise, though I was thinking of using two plastic storage crates stacked on each-other. Thanks for sharing.

[Dan Hintz]

You're welcome. I keep thinking about redoing it all using different materials, easier to assemble, etc., but so far it has worked well enough that's it really hasn't been worth the trouble to do so.

Some day... maybe...

[Joe Hillmann]

I just wanted to bump this to let people here know that I just ordered some activated carbon from General Carbon to build a filter and that so far they are about the best company I have ever worked with. I called them up not knowing exactly what I needed and feeling kind of stupid asking. I talked to a guy named Irwin and he gave me all the information I could need to build a filter and told me to call back if I have any questions. He told me what to expect for static pressure drop (2in of H20 per foot of carbon) what velocity (50-60 feet per minute) and that if I get the air going too fast (around 100 feet per minute) that the carbon will begin falling apart, and that using mosquito screen is a great way to hold it in place.

[Steven Cox]

Thanks so much for this thread, I've been following it for some and it has given me some good ideas to enable me to build my own system. What I did differently was incorporate the filters (pre filters, charcoal & HEPA) into my exhaust stack which is a length of colorbond rectangle downwater pipe. If anyone is interested I'll post some pics at a later stage to show the workings.

The biggest problem I had was calculating volumes to help ensure my exhaust fan could handle it and because some parts are cylinder shapes - others rectangular and not being that good at math beyond basic calculations I found the calculation tools on the following website very useful. I hope this link can help others too:

http://www.calculatoredge.com/enggcalc/volume.html

Also to moderators when it comes to lasers ventilation is such an important issue when considering WPHS so I think this topic should be a Sticky to avoid it being lost.

[Joe Hillmann]

Thanks so much for this thread, I've been following it for some and it has given me some good ideas to enable me to build my own system. What I did differently was incorporate the filters (pre filters, charcoal & HEPA) into my exhaust stack which is a length of colorbond rectangle downwater pipe. If anyone is interested I'll post some pics at a later stage to show the workings.

The biggest problem I had was calculating volumes to help ensure my exhaust fan could handle it and because some parts are cylinder shapes - others rectangular and not being that good at math beyond basic calculations I found the calculation tools on the following website very useful. I hope this link can help others too:

http://www.calculatoredge.com/enggcalc/volume.html

Also to moderators when it comes to lasers ventilation is such an important issue when considering WPHS so I think this topic should be a Sticky to avoid it being lost.

Of course we want to see pictures.

[Dan Hintz]

He told me what to expect for static pressure drop (2in of H20 per foot of carbon) what velocity (50-60 feet per minute) and that if I get the air going too fast (around 100 feet per minute) that the carbon will begin falling apart, and that using mosquito screen is a great way to hold it in place.
Your layer should only be a few inches thick, at most (mine is around 2"), so we're talking tenths of an inch drop in pressure. Of course, I'm not sure what he meant by the air going too fast causing an issue. It would depend upon the surface area of the carbon layer, but even at around 1 square foot, I'm cranking quite a bit more than 100CFM through it (easily 5x more than that) and there's no problem with it falling apart.

[Joe Hillmann]

Dan, not cfm, just feet per minute. He also recommend going with a thicker bed(I asked if 6 inches would be enough and he said it would be more than enough)and also that the air only has to be in the carbon for tenths of a second to be cleaned.

On your system do you have any type of metallic screen to filter out any burning embers before they get into the carbon? I ask because I got to thinking that in the off chance that a burning ember got into the carbon and the air kept flowing over it it could become a very hot fire before you had any clue anything was wrong. I don't think that I have ever had anything on fire ever make it into my ventilation system but the way I have it now even if it did it is all metal until it is outside then it is a brick wall so I have never been concerned with a fire once it was out of the laser.

[Dan Hintz]

It hits a furnace filter first, but no wire screen... any wire screen with a mesh small enough to catch burning embers will be too small to allow a good airflow (think much smaller than screen door).

[Joe Hillmann]

It hits a furnace filter first, but no wire screen... any wire screen with a mesh small enough to catch burning embers will be too small to allow a good airflow (think much smaller than screen door).


I guess I am more thinking of larger pieces of paper that may get sucked in with just a small corner or edge burning and thinking even 1/4 woven wire would be better than nothing and then after that a layer of metal window screen. But you are right neither of them would stop very small pieces from getting sucked into the carbon, I wonder if some type of cyclone would be a good idea.

[Dan Hintz]

I don't have any issues with small bits catching on fire and getting sucked into the exhaust... if I'm catching things on fire, my settings are wrong or something is out of whack. Either way, I don't leave my machine unattended, so I can keep track of what's happening. It's a concern, but not a big one (at least for me).

[Steven Cox]

Of course we want to see pictures.


As you can see by the pics below its pretty simple. The white moulded bit (flue Adapter) is a part off an Arlec portable airconditioner but if you do an image search on google for Flue Parts you'll see parts like this are readily available, it's just I had this lying around. The hatch cover on the vehicles canopy is an inspection porthole that I got from a boat shop. Anyway all I needed to do with this was make the Flue Adapter capable of holding the charcoal. So, I just done some measurements and cut the parts from scrap acrylic and added some Insect Screen.

I changed the laser to vent from the left side instead of the back and with some 150mm duct flanges, connected the laser cabinet to the canopy/Inspection hatch. My mere fluke the Flue Adapter fits perfectly into the Porthole with no gaps. The exhaust air flows directly from the fan into the Flue adapter with holds the charcoal. From the fan to the Charcoal the air only flow 150mm (6 inches). Once the air goes through the charcoal its forced up the tube to the top where its vented out. Just before the vents at the top I have the Hepa filter which is not shown (didn't feel like pulling that apart).

The Flue Adapter holds 1.5Kg of charcoal which is about 100mm deep (4 inches). We've been operating at different venues with this system for over 12 months and nobody has complained of any smell comming from the exhaust stack.

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[Steven Cox]

The Flue Adapter holds 1.5Kg of charcoal which is about 100mm deep (4 inches). We've been operating at different venues with this system for over 12 months and nobody has complained of any smell comming from the exhaust stack.

I should point out that we only user the laser 2 or 3 days a week and actual running would max 3 - 5 hours a day. I change the charcoal & filters every 3 months and before the fan I have a piece of foam in front of the fan on the laser side to catch larger particle. The foam itself is about 10mm thick but its open weave so you can see through it. It's also washable, so I clean it every week and it cuts down on the amount of crap hitting the fan as it vents, so that's got to be good for the fan.

[Joe Hillmann]

Steve, Do you have any problems with the laser caused by moving it all the time? I have thought of taking my little 35 watt with me when I go to shows but decided against it because I was afraid that moving it all the time might cause damage?

Also do you take and special precautions when you move it?

[Steven Cox]

Steve, Do you have any problems with the laser caused by moving it all the time? I have thought of taking my little 35 watt with me when I go to shows but decided against it because I was afraid that moving it all the time might cause damage?

Also do you take and special precautions when you move it?


Yes, I pack the tube in the machine and ensure its not touching any part of the cabinet or mounts. Additionally I secure the laser head in position so it doesn't move with velcro straps. I also wind up the table with a piece of 12mm ply on top so the ply locks against the cabinet/gantry frame. Other than that the laser cabinet is sits on a rubber mat and is securely bolted down.

Really you've just got to think about how the manufactures pack and send the lasers paying particular attention to what has been tied up/secured inside the machine and try to duplicate and improve on that, more is better. I used double sided velcro straps for quite a few things...... velcro is my friend! Setting up though you need to re-align the tube and depending on how level your vehicle is you may need to shim the tube to align it. I rearly have to adjust the mirrors themselves.

Have a look at my posts in this topic there's some more tips there: http://www.sawmillcreek.org/showthread.php?181819-Chinese-Shenui-Laserworks-tips-and-tricks-thread&p=1883163#post1883163

[Jared Gaylord]

Hey Dan what do you think about this fan with the filter? It is what my Epilogue Rep suggested he said it would be a bit overkill but..... I just want to find something that will work with the filter but not run everyone out of the house with noise!!! Thanks a bunch

http://www.pennstateind.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PS&Product_Code=DC3XX&Category_Code=dust-collectors

[Dan Hintz]

I would again suggest the Harbor Freight greenie... it's an induction motor, so quieter than a brushed unit, and can be had for <$100 with sales.

[Pete Bejmuk]

Dan, I am going to be building a similar scrubber. I found a local(-ish) charcol supplier in NE, and they have a variety of different types of activated charcol: http://www.buyactivatedcharcoal.com

They have various types charcoal: coconut charcoal, bamboo charcoal and hard wood charcoal, "Norit Supra Charcoal"... available in bulk in powder and in pellets. I'm assuming powder is what I need (for the best surface area) but I'm not sure what I need, would the "PAC-325 Powder Activated Carbon" $97 for a 47 pound bag. Would that work?

[Randy Digby]

Pete, what I use is a small pellet form, much like the pile on the left side of the top picture in your link. I'm thinking you need some separation to obtain good air flow through the charge. Then again, I haven't tried the powder. I'm sure Dan will respond as well. Good luck on your project.

[Dan Hintz]

Randy's right, you want pellets. There would be several hundred square feet of surface area with several inches of pellets several mm in size/length. If you went with the dust, you'd need to contain it in some way that would allow airflow through it without blowing it out of the duct.

[Shawn Conklin]

Hi Guys, Wanted to jump in on two things

1. General Carbon was an awesome company to work with (as mentioned earlier in another post). I just ordered from them yesterday and had the shipment 22hr later ! They are in NJ so fairly close to us (we are in NY 2hrs north of NYC). But still very fast times and were very knowledgeable. Seems they have worked with quite a few of us laser folks. http://www.generalcarbon.com/vapor.html I picked up the GC A-40. They said that the less expensive GC C-40 is fine for external venting but we vent inside and want maximum absorption. Plus the price difference isn't much on as 55lb sack.

2. We use a 'pro' built filtration system made by Purex. The filters use carbon pellets of the 4mm size. So if your looking to model after something used in clean rooms, there you go.

I can't imagine any way to use a powder with high air flow. You would need a hepa filter after the carbon just to keep it from dusting over the room :-)

[Tom Schulze]

So, during my planning for my filter build I did a quick search for charcoal and found it on amazon.com. a 52lb bag for around $51.00 shipped. do a search for "LV CARBON BAG 52LB BULK" to find it. I thought you would all like this info. here is a picture of the charcoal I received. the pieces were all around 3.5mm some smaller some larger.

231275

[Dan Hintz]

Currently on sale for $40, and comes in a cleaner plastic bag... nice find.

That brings my filtration unit cost to <$150 :)

[Glen Monaghan]

I picked up a couple of pleated air filters, both 16"x19"x4", one a "whole house air filter with electrostatic fibers" rated MERV 13/APR 1900 and the other a HEPA filter. Coupled with an 8" inline fan rated 700+ CFM, I get impirically good exhaust rate from my laser and the effluent is visibly smoke free, but not odor free. I'm especially interested in removing the odors from cutting acrylic.

Looking at a few commercial filters for lasers, they show similar prefilter and HEPA filter coupled with a rather deep "chemical" (ie, active carbon) filters, as in 8"-12", but it looks like most people here are talking 3-4" of carbon granules. Also, the commercial units place the HEPA filter before the carbon, presumably to help prevent clogging the carbon pores with smoke and cooling acrylic vapors, whereas the talk here looks like the HEPA filter is after the carbon.

Not clear whether the commercial units have so much carbon more because it's needed to control odors, or more to extend the useful life between carbon changes... Also, it seems to me that the whole point of the carbon is to address gaseous odors while the HEPA filter is supposed to deal with particulates (smoke) and such, plus the HEPA filter is less expensive than 50 pounds of activated carbon (which would be needed to make a similarly sized carbon filter), so better to put the HEPA first and keep as much crud out of the carbon as possible?

I'd like to know if any of you using self-built filters have thoughts based on your experience, regarding HEPA>Carbon vs Carbon>HEPA order, and amount of carbon needed to control acrylic odors. TIA

[Dan Hintz]

You're pretty much right on the money with your thinking, Glen. A deep filter bed will cut down on change frequency, but it will also reduce CFM and inches of H2O. There will always be a lingering smell from the product itself (and inside the laser cabinet), but there should be little to none during actual processing. I chose to put the HEPA last because I didn't want charcoal dust flying around in my workshop (and in my lungs). You will need to tap it clean every time you change the carbon, but that's no big deal. The commercial filters do not have that issue... the carbon is trapped within the filter, and there is little dust to deal with.

[Robert Silvers]

Reflecting on this post, if you had to start over - what about just buying one of these eBay units designed to keep people from smelling your weed?


Are they appropriate for the laser?

[Dan Hintz]

It would make for more convenient changes of the carbon filter, but this does not include a HEPA filter nor a bulk capture filter, and the entire unit would still need a housing to control airflow through each filter.

[Robert Silvers]

On the typical Chinese laser, what size duct do they use? I want to buy a grow-house unit that fits the same duct size, and then I will find a way to get a HEPA after it.

Speaking of which, what about not using a HEPA after it, but using something like this after the charcoal?

http://www.amazon.com/Honeywell-CF100A1009-4-Inch-Efficiency-Cleaner/dp/B001E96Q6S/ref=pd_sim_hg_1

[Robert Silvers]

http://www.epa.gov/iaq/pubs/airclean.html




Medium efficiency filters with a MERV of 5 to 13 are reasonably efficient at removing small to large airborne particles. Filters with a MERV between 7 and 13 are likely to be nearly as effective as true HEPA filters at controlling most airborne indoor particles. Medium efficiency air filters are generally less expensive than HEPA filters, and allow quieter HVAC fan operation and higher airflow rates than HEPA filters since they have less airflow resistance.
Higher efficiency filters with a MERV of 14 to 16, sometimes misidentified as HEPA filters, are similar in appearance to true HEPA filters, which have MERV values of 17 to 20. True HEPA filters are normally not installed in residential HVAC systems; installation of a HEPA filter in an existing HVAC system would probably require professional modification of the system. A typical residential air handling unit and the associated ductwork would not be able to accommodate such filters because of their physical dimensions and increase in airflow resistance.



http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf

So it looks like MERV 13 or better is decent.


Here is a MERV 12:

http://www.amazon.com/Honeywell-CF200A1008-4-Inch-Efficiency-Cleaner/dp/B001E96Q7C/ref=sr_sp-atf_title_1_3?s=home-garden&ie=UTF8&qid=1375135304&sr=1-3&keywords=HVAC+filter

MERV 13:

http://www.amazon.com/Nordic-Pure-14x24x1M13-6-14x24x1-Pleated/dp/B005ESORZC/ref=sr_sp-btf_title_1_4?s=hi&ie=UTF8&qid=1375135676&sr=1-4&keywords=MERV+14

15:

http://www.amazon.com/Carrier-Bryant-Infinity-Replacement-Filter/dp/B002AUSS98/ref=sr_sp-atf_title_1_1?s=hi&ie=UTF8&qid=1375135707&sr=1-1&keywords=MERV+15

16:

http://www.amazon.com/Lennox-X6666-MERV-16-Filter/dp/B004X4UO0K/ref=sr_sp-btf_title_1_10?s=hi&ie=UTF8&qid=1375135746&sr=1-10&keywords=MERV+17

http://www.amazon.com/X6675-Lennox-20x25x5-Filter-HCC20-28/dp/B000PY2EZA/ref=sr_sp-btf_title_1_4?s=hi&ie=UTF8&qid=1375135801&sr=1-4&keywords=MERV+20

[Dave Sheldrake]

On the typical Chinese laser, what size duct do they use?

100mm, 125mm and 150mm normally depending on machine size.


I want to buy a grow-house unit that fits the same duct size

I've done the same on my home laser (the one I play with when I'm not working) seems to work very well but I don't need "breathable air" coming out as it still vents to the outside (I just wanted it to smell nice for the neighbours)

best wishes

Dave

[Dan Hintz]

My HEPA cost $50... tough to beat that.

[Robert Silvers]

My "laser" has a 150mm exhaust. I ordered a 6x26" scrubber from eBay. Cost $89 shipped. Has 2 inch thick layer of charcoal.

I will use a 6" elbow through the side of a 44 or 50 gallon trash barrel and then seal a MERV 13 HVAC filter onto the top of the barrel.

[Robert Silvers]

Just got this from eBay for about $90. Seems like a really good deal.

http://imageshack.com/scaled/large/62/zbvt.png

[Dave Sheldrake]

Just got something similar Rob, the only downside is the air has to travel from outside to inside to prevent the filter clogging. Did you get a prefilter kit with it?

best wishes

Dave

[Robert Silvers]

It came with a prefilter wrap.

I didn't know that - but I will set it up that way. I will go to Lowes and look for a trash barrel or plastic container and a way to rig it.

[Dave Sheldrake]

Just been playing with mine Rob, it reduces the smoke but doesn't remove it totally,

I have a fan extracting to a wooden sealed box with the filter inside the box and a second fan pulling from the filter to atmosphere.

I'll keep it going for a while longer and see what happens but so far it's not going to be "inside room" capable for sure on mine.

cheers

Dave

[Robert Silvers]

I have 2 inches thick of carbon. Do you have 1, 1.5, or 2 inches thick?

[Robert Silvers]

I want to work one of these into it:

http://www.amazon.com/24000-Honeywell-Cleaner-Replacement-Filter/dp/B0009H798U/ref=sr_sp-btf_title_2_24?ie=UTF8&qid=1375485924&sr=8-24&keywords=HEPA+filter

[Dave Sheldrake]

2 inches of Carbon Rob, I'm lacking the HEPA though that Dan used in his which is where I'm probably losing the performance.

It's great on acrylic but on a 180 watt cutting MDF it only reduces the smoke by around 40%. I'm off into town tomorrow to find something similar to yours and Dan's HEPA to add that in and see what happens.

best wishes

Dave

[Dan Hintz]

When I'm engraving/cutting heavy wood (large wood plaques and such), I get zero smoke in the room after a couple of hours of straight work. First it hits a furnace filter, then the 2" bed of carbon, and finally the HEPA. I purchased one of those Honeywell Electronic filters thinking I could trap a lot of smoke that way and increase my carbon life... I skipped it after I determined the amount of airflow would make it all but worthless, and I'll likely install it in the home HVAC next remodel session.

[Dave Sheldrake]

I'm venting outside Dan but smoke on the home laser / test machine is something I'm trying to cut down. I have a 150mm inline from the machine to a sealed box with the unit like Rob has flowing in to a second 150mm inline then out to atmosphere. I'm wondering if adding a hepa in front of the carbon can will reduce the smoke?
I could just go buy a commercial air cleaning unit but I like tinkering ;)

cheers

Dave

[Glen Monaghan]

Seems like a really good deal in what way?

I got one of these incidental to acquiring the 8" fan unit I was getting. These things come with either 1", 1.5" or 2" thick layers of what is supposed to be activated charcoal (it's definitely charred, but I don't know how to verify that it's activated carbon).

All I can say for sure is that the stuff is charred pieces on the order of 0.5" chunks rather than granules, and even the 2" thick versions don't allow for much "contact" time with the air getting sucked through. Consequently, my empirical test showed these things are inadequate for removing odors, especially when cutting acrylic.

You can get 55 pounds (at least twice as much carbon as these canisters hold) of GC 4x8S activated carbon granules from General Carbon for $99 plus shipping. I was looking at commercial filter units at the NBM show and they typically pull air through at least 10" of carbon for odor removal with small to medium sized laser machines.

[Glen Monaghan]

By "great on acrylic" I assume you mean removing visible smoke, rather than the odor?

These things are generally unsuitable for filtering smoke because they have relatively HUGE chunks (about 1/2" diameter) of charred material, layered about 2" thick. You will have rather poor smoke removal and fairly quickly clog up the charcoal with what smoke particulates it does filter, ruining whatever odor removing ability it may have.

[Robert Silvers]

When I'm engraving/cutting heavy wood (large wood plaques and such), I get zero smoke in the room after a couple of hours of straight work. First it hits a furnace filter, then the 2" bed of carbon, and finally the HEPA. I purchased one of those Honeywell Electronic filters thinking I could trap a lot of smoke that way and increase my carbon life... I skipped it after I determined the amount of airflow would make it all but worthless, and I'll likely install it in the home HVAC next remodel session.

Does the furnace filter capture a lot of stuff? Does it get very dirty? Do you know the MPR or MERV rating for it?

[Robert Silvers]

A good deal in terms of the packaging (metal container). But if commercial laser filters are 10 inches of carbon, then these units are not good enough, and it sounds like raw carbon contained between two screens is the way to go. But Dan says that his 2 inches of carbon seems good, right?

[Glen Monaghan]

That's what he said. I just received some of the General Carbon product but haven't had time to test it. However, the stuff in that canister was basically ineffectual when I tried exhausting through it while cutting acrylic, and only somewhat helpful when cutting BB ply. I used a 4" thick 19x16 whole house filter followed by a 4" thick 19x16 HEPA filter for smoke, which worked great, and then the canister for odor, which was a fail as mentioned.

[Dan Hintz]

I'm wondering if adding a hepa in front of the carbon can will reduce the smoke?
A HEPA will definitely reduce your smoke (that's what they're there for)... but you'll fill that filter up in a heartbeat. You'll get the most bang for your buck if you let the HEPA get rid of just the final remnants... a thick layer of activated carbon should cut down on your smoke significantly.


Does the furnace filter capture a lot of stuff? Does it get very dirty? Do you know the MPR or MERV rating for it?
No MERV rating (at least one I care about). I have two layers of it... the top one is to catch bulk material (like physically viewable chunks of material that came off of the vector table during cutting), and the other is mostly there to hold up the activated carbon. Smoke and such will go through them, for the most part.


A good deal in terms of the packaging (metal container). But if commercial laser filters are 10 inches of carbon, then these units are not good enough, and it sounds like raw carbon contained between two screens is the way to go. But Dan says that his 2 inches of carbon seems good, right?
The 2" I put in mine seem to do a nice enough job, but then again I didn't want to put in a thick, thick layer and have air flow drop significantly. In my next design iteration, I may increase the thickness to 3" just for completeness.

[Dave Sheldrake]

By "great on acrylic" I assume you mean removing visible smoke, rather than the odor?

More the odor, I don't have too much trouble with the acrylic smoking it's more the smell (that my wife happens to like but I hate). The can filter works ok for that (I'm extracting outside anyhows).At low power (60 watts or so) there is quite a bit of smoke from the acrylic but once it goes to 160+ watts the smoke almost vanishes.
My work filter system is huge and vents clean air (it gets inspected by the HSE on a regular basis because of the UK's "clean air act") so I really just like to toy around at home to see what can be done.

I'm off to town to see what bits I can get :)

cheers

Dave

Looks like I'm going to be pulling mine to bits and seeing if I can add loose carbon then the hepa.

[Glen Monaghan]

A HEPA will definitely reduce your smoke (that's what they're there for)... but you'll fill that filter up in a heartbeat. You'll get the most bang for your buck if you let the HEPA get rid of just the final remnants... a thick layer of activated carbon should cut down on your smoke significantly.

As I read the literature, a true HEPA filter is actually overkill for most smoke particles. High-MERV non-HEPA filters (especially electrostatic types) appear sufficient for removing most smoke, are less expensive than HEPA, and won't clog so quickly. Consequently (and being a cheap b@st@rd), my build is using a High-MERV as pre-filter and then HEPA for the really fine stuff. Also using fairly large and deep filters to minimize air flow restriction and maximize life, compared to the much smaller canisters some people are talking about.

As for using activated carbon to filter the smoke, General Carbon says running smoke through the carbon is a quick way to clog up the pores and prematurely destroy the carbon's effectiveness. They also noted that non-visible vaporized compounds from cutting acrylic and other plastics tend to coat and quickly clog activated carbon as well. They recommend using the activated carbon as a "polisher" after other filters, more as an odor remover than a particulate remover.

As Dan noted previously, having the carbon last in the filter stack means you could have fine carbon blowing out the exhaust for a while when you change the granules out, so he put his HEPA after the carbon. My build is using 4 identical 16x19x4" filter bays in which the filters can be arranged/rearranged as desired. One for prefilter, one for HEPA filter, one for activated carbon filter, and final open/optional bay for a possible post filter or, more likely, second carbon filter (I intend for each carbon filter to be 1/2 the 55# bag of GC's granules, so using both means I wouldn't have to store half a bag of carbon somewhere else, and presumably means I could go about twice as long before needing to change out the carbon). Because the bays are identical, if using only one carbon filter, I can drop the HEPA filter from 2nd to 4th bay for a while after changing the 3rd bay's carbon, to catch carbon dust. Or, if I go with 2 carbon bays and change the granules, just swap the HEPA and 2nd carbon until the dust clears, then switch them back.


The 2" I put in mine seem to do a nice enough job, but then again I didn't want to put in a thick, thick layer and have air flow drop significantly. In my next design iteration, I may increase the thickness to 3" just for completeness.

No idea what your fan specs are, but the GC4x8 granules have a pressure drop curve that ranges as follows:
0.3" water per foot of carbon granules at ~21 fpm superficial airflow velocity
1.0" water per foot of carbon granules at ~48 fpm superficial airflow velocity
2.0" water per foot of carbon granules at ~75 fpm superficial airflow velocity
4.0" water per foot of carbon granules at ~110 fpm superficial airflow velocity
5.0" water per foot of carbon granules at ~125-130 fpm superficial airflow velocity

[Zach Radding]

I know this thread is a little old, but thought someone searching through the archives, might like to see what I did for a DIY fume filter. It cost a bit more than $200 (actually double that), but I posted a step-by-step on how to build it here:
http://www.instructables.com/id/Build-a-laser-cutter-fume-extractor/

[Jerome Stanek]

I am thinking of something like that also. I cut a lot of acrylic.

[Dan Hintz]

what I did for a DIY fume filter. It cost a bit more than $200 (actually double that)

Kudos to an interesting design, Zach. Very modular in nature, and I bet if you removed the fan from your parts list, the final cost will be a lot closer to my $200... $60 for the filter, $100 for the carbon, and $40-50 in miscellaneous.

That said, I do notice you're not using a HEPA filter in yours, and that can be a big deal when handling a lot of the junk that comes from burning materials like acrylic and wood. Also, if I view your design correctly, the laser fumes will hit the filter before the carbon... that will clog your filter very quickly when you're dealing with high-particle materials like wood. To be fair, mine suffers from a similar malady where the carbon gets gunked up fairly quickly (the HEPA comes after the carbon on mine), but that's much cheaper to replace.

It's funny you should bring this thread up, as I was just thinking of a new design this morning, more of a stackable setup than inner-to-outer, but I still wish to improve upon my earlier design (both in terms of efficiency and in ease of replacement for each section/cartridge). I was leaning towards an aluminum extrusion design this time around, though the details still need hashing.

[Glen Monaghan]

I went with a whole-house filter that is nominally 16x19x4 inches to serve as a relatively inexpensive sacrificial prefilter. I also found a 16x19x4 HEPA-class filter so decided to go with 16x19 for the activated charcoal (AC). Because of the amount of AC in the bag I bought, I opted to go with a 16x19x5 tray of AC (which is actually more like 4.5" of AC because I used an adjustable-sized foam furnace filter on the bottom of the tray to retain the AC), then decided to allow for an optional second 16x19x5 tray of AC, both because I had enough AC to do it and because the commercial unit I looked at appeared to have about 8" of AC so I thought I might need or at least want it.

I find that a single AC tray is fine for cutting BB but have been using both AC trays because using just one lets too much smell through when cutting acrylic. Sufficient space was available so I chose 4 inch thick, deep pleated 16x19 pre- and HEPA filters to provide a large surface area for lower restriction and longer life, and made all four filter bays big enough to handle any filter so that I could play around with different combinations if desired. I've placed the HEPA after the AC to minimize possibility of carbon fines making their way into my lungs.

I had laminated sheet stock left from building a cabinet for the laser to sit on (and to hold some drops in progress, fixtures for often-repeated jobs, a few tools and cleaning supplies, etc.), so I used that to make a matching filter tower that sits beside the cabinet. Opted for a down draft arrangement, with inlet being smooth 8" duct going to laser (transitioned there to match laser's 4" port) and outlet being a 12x12 inch grille at the bottom of the tower as shown in the image.

[Zach Radding]

Hey Dan, The general modular design is not mine. It was highly "inspired" by the Electrocorp design, but modified to make it easy to build DIY. The filter I am using claims to be HEPA. The pre-filter takes a good portion if the particle load before the HEPA. We'll see how long it lasts....

[Dan Hintz]

Glen,

The stacked design is what I'm designing around this time around, but I'm going to attempt one without an outer cabinet to reduce weight. I'm thinking each stack will have tubes on the corners that threaded rod will fit through. Once you have everything stacked up, a wingnut at the top will snug every layer together.

[David Somers]

Dan,

If you have an android or iphone you can get a db meter app that is decently accurate. Cost is $1 or less. Might be able to find a free one as well.

Wouldn't satisfy OSHA, but it would give you a decent ballpark sound level to compare with. Looks like this thing will knock the sound down 5 to 10db? That is not a large amount depending on the starting point. 90db would be a typical lawn mower. 60db is normal conversation. Just for reference.

I have a 1HP version of that unit at home and will check its sound level when I get home tonight and report back. I never found it to be really loud, but hate having it on for long periods.

Completely off topic, but when I lived in HI we were in the process of being infested with Coqui frogs....an accidentally and recently introduced invasive species from Puerto Rico. With no predators they got population densities high enough that their combined night time calls would hit 90 db. Absolutely amazing to hear. Hopefully your unit is not quite that loud. <grin>

[Dan Hintz]

The red beast from Harbor Freight is a real screamer... supposedly the green one is much quieter, though you can't control the speed with the router control variable speed module, so it's a trade-off. If I ever get around to putting a sound screen around my shop DC, I'd use that instead, but without the screen it's even louder than the read beast (3HP).

[David Somers]

I have to admit, that is one thing I love about working on the lathe. As far as wood working power tools go it is one of the quietest. Pretty lovely to sit there working away on a big bowl or a small finial and just hear the Shoop Shoop of the wood being cut against the gouge. It is rude to finally start sanding this time of year and have to use the dust collector.

Any....will be home in a few hours and will get those readings for you for comparison sake.

Later!!

Dave

[Jerome Stanek]

The red beast from Harbor Freight is a real screamer... supposedly the green one is much quieter, though you can't control the speed with the router control variable speed module, so it's a trade-off. If I ever get around to putting a sound screen around my shop DC, I'd use that instead, but without the screen it's even louder than the read beast (3HP).

I tried the red one and it is a lot louder than the green ones. I had both of the green units and i would say they are about the same noise level

[Glen Monaghan]

Should work, as long as the layer walls are sturdy enough. My carbon trays have quarter inch thick wood sides which should be strong enough but would probably need a filler piece in each corner to receive the threaded rod. The HEPA and pre filter are just typical cardboard construction so they'd have to go into similar trays. And you'll probably want some sort of "weather stripping" to seal each layer to the next. The laminated sheet stock I used definitely is heavy, but I put the tower on casters in case I should ever have reason to move it, which I didn't really expect. Turns out to have been a good idea since I'm going to be moving to a new facility in about 3 weeks...

You'll have the freedom to use whatever filter dimensions you want without concern for finding or making a suitably sized enclosure (well, sort of, you'll have to come up with each tray and maybe a fan housing, depending on whether the fan is going to be part of the stack or a separate unit), and you could separate the layers for easier transport if needed. My biggest concern is having to disassemble the stack just to check or change a filter layer. I simply pull the door and slide a filter out, inspect/replace, and pop the door back. With threaded rods, you'll have to unscrew either the nuts or the threaded rods on each corner, then either remove the rods or else lift each layer up and off until you get to the one(s) you want, inspect/replace, align each successive layer and mate to the rods again, and finally rejoin and retighten nuts and rods. Maybe a framed 1/4" thick plywood box might be less bothersome yet not too heavy?

[David Somers]

Dan,

My dust collector fan is a 7amp 1.5 hp unit from GHC in China. I think i bought it at lowes or Harbor Freight a long time ago. Perhaps 10 years?

Anyway, from 3 feet away it is 74db.

dave

[Mark Olmstead]

I finished my filter system per Dan's layout and must say that it does not work as well as anticipated, especially when cutting acrylic. I've increased the carbon layer to almost 4" and the smell is still very noticeable. I'm going to either slow down the airflow speed or increase the depth of carbon with another layer and see if it helps.

[Dan Hintz]

Mark,

How much surface area are you providing for the carbon bed? Are you using the pre-(static) and post-filters (HEPA)?

Too fast of an airflow will certainly cut down on how much is captured... what kind of a collector are you using (power)?

[Glen Monaghan]

My layout has spaces for up to 4 filter trays, each 16"x19" and 4" deep. The first one has a whole-house filter (Accumulair Diamond) to serve as pre-filter, catching bigger stuff. The last one is a 4" thick HEPA filter. The middle is for activated carbon. One 4" bed of AC doesn't remove enough smell for me when cutting acrylic but using both middle trays with 4" of AC does the trick. Just weighed them after 3 months and they've gained a bit more than 10% in weight.

Need an airflow/airspeed monitor to determine when is good time to change the pre- and post-filters... A fine particulate meter would be nice to check the quality of the HEPA filter, too...

[Mark Olmstead]

Mark,

How much surface area are you providing for the carbon bed? Are you using the pre-(static) and post-filters (HEPA)?

Too fast of an airflow will certainly cut down on how much is captured... what kind of a collector are you using (power)?

Hi Dan,

I used your design as a springboard to make what you see here.

Central Machinery 660 CFM blower
I have two layers of activated charcoal, 20"x14", each two inches deep (about 25 pounds worth) Pre filters before the carbon layers, hepa filter after.

I designed this so it would be really easy to change out the carbon and filters, so I'd love to know what I did wrong. The airflow is not too fast, the amount of air coming out the blower exhaust is less than a hair dryer on high. But cutting paper or wood, there's haze in the garage after about 5 minutes of running ever since I made it.

[Dan Hintz]

Hi Dan,

I used your design as a springboard to make what you see here.

Central Machinery 660 CFM blower
I have two layers of activated charcoal, 20"x14", each two inches deep (about 25 pounds worth) Pre filters before the carbon layers, hepa filter after.

I designed this so it would be really easy to change out the carbon and filters, so I'd love to know what I did wrong. The airflow is not too fast, the amount of air coming out the blower exhaust is less than a hair dryer on high. But cutting paper or wood, there's haze in the garage after about 5 minutes of running ever since I made it.

For one, the extra (unnecessary) twists and turns you're forcing the air to move along will really slow things down. If the piping is coming from up top, put the HEPA filter in the top... that gets rid of 180 degrees in bends. From the looks of it, you also have a 90 degree bend (or the equivalent of one) going from the machine to the filter stack. Also, you restrict the flow of air from bucket to bucket by forcing it through a pipe... one section to the next should be wide open.

You have a serious number of restrictions there, so it doesn't surprise me you have serious flow issues.

[Jacob Davalos]

Dan,

are you still using this system, has it held up? Do you use it to put the exhaust back into an enclosed room, or do you filter and then release outside?

[Mark Olmstead]

Hi Dan,

Thanks for the reply and your trying to help me with this. So you're saying that if I cut down on the bends in the ducting, that will increase the airflow. Are you then suggesting that with this increased airflow, the carbon will extract more fumes? I thought you said if air flow is too high, it can pass through the carbon layers too quickly. I don't have any issues with airflow, the smoke and fumes are being pulled from the laser just fine. It's the smoke and fumes not being removed from the air before it leaves the extractor that I'm having issues with.

[Glen Monaghan]

Seriously consider eliminating the pipes between sections. Instead, cut matching holes in the lid of the lower bin and the bottom of the next higher bin (the holes would ideally be about the same length and width as the filter media), and use come closed foam gasketing to seal the junction. For the top bin with the HEPA filter, you can get a box-shaped filter that will provide a lot more surface area, resulting in less flow resistance. Even if you stick with that cylindrical filter, it would be better to exit straight up through the lid to eliminate the nearly 180 degree bend in the outlet pipe.

You can see the measurements of the system I built in a previous post here, but my experience was that one 4" bed of activated charcoal was not sufficient to remove all the orders, but two 4" beds works fine.

If you are getting smoke/haze in the room, then either your "HEPA" filter is NOT really a HEPA filter, or you have a significant leak somewhere before that filter. A true HEPA filter would not allow visible smoke/haze to pass through.

[Mark Olmstead]

Glen,

Thanks for the reply, I really appreciate you giving this some thought. I found the airflow restriction was due to the hepa filter having a lot of stuff on it, I cleaned it out and air flow is really good now. I now have a much better initial filter to eliminate this problem.

Regarding the haze and smoke, a leak before that filter seem like the logical conculsion. But I'm not sure how that could be the case since the blower is actually pulling the air through the filter system and the entire system is under vacuum. Since the hepa filter is right before the blower motor, the only way the air can get out of the system is through that filter (and I'm sure it is a HEPA filter). I'll look into making the holes larger between the two bins with the carbon, maybe the problem is that the air is so concentrated that only a small portion of the carbon is coming in contact with the air.

[Dan Hintz]

Thanks for the reply and your trying to help me with this. So you're saying that if I cut down on the bends in the ducting, that will increase the airflow. Are you then suggesting that with this increased airflow, the carbon will extract more fumes? I thought you said if air flow is too high, it can pass through the carbon layers too quickly. I don't have any issues with airflow, the smoke and fumes are being pulled from the laser just fine. It's the smoke and fumes not being removed from the air before it leaves the extractor that I'm having issues with.

As Greg said, if any smoke is making it past the HEPA, you don't have a HRPA (or a leak)... that said, if you have that level of smoke getting to the HEPA, it will be filled of particulate matter (and rendered useless) in a very short time. If you notice VOCs coming through, you have the option of making your carbon bed thicker or slowing down the airflow.

Also, if you don't sandwich the carbon between filters, you run the risk of levitating the carbon with high airflows, which will reduce cleaning efficiency. I chose to run the air downwards, letting gravity and the airflow work together to keep the carbon packed.

[David Somers]

Morning all,

Since this has been a long running thread I thought I might provide an update. I was checking on carbon prices recently as I ever so slowly prepare to buy a laser someday. I contacted sales at General Carbon, the source Dan Hintz originally mentioned. They said they no longer had the 3mm pellets in stock but felt the 4mm pellets would do just as well for this use. Part number C-40. $121 for 55b bag with about $53 SH from NJ to Seattle. (apparently too big for a forever stamp....sigh) They also said part number GC 4x8S at $90.75 for a 55 pound bag would perform equally in this case and was less expensive. Same S&H.

Also, not sure if this changes the pricing at all, but Dan had mentioned he bought his HEPA filter from Sears. All the Sears stores out here seem to be going out of business at the same time. Might be worth checking your local Sears store to see if you can get a filter at a better price if they are offering Going out of Business Sales. Prices for them overall seem to have gone down a modest amount since the thread started way back when.

Hope this helps someone! And thanks Dan for shepherding this multi year thread all this time!!

Dave

[Gary Hair]

Is all activated carbon alike? I found some that is marketed for fish tanks that is about 1/2 the prices elsewhere but it says it's for fish tanks.
Here is a link to the manufacturer:
http://www.acurel.com/index.php?option=com_k2&view=item&layout=item&id=17&Itemid=75

[David Somers]

Gary,

The variance is in the size of the charcoal and the material it is made from. What gets used in fish tanks is often a finer material than what gets used for air filtration. the finer particles makes it harder to move a volume of air through it. The size of the particles in the stuff I mention above is 4mm cylindrical pellets. Stuff used in aquariums tends to be crushed into a much smaller grit.

Although it is not the case with the Charcoal I mentioned above, many air system charcoals have chemicals added to them to help remove certain types of gases as well, depending on the needs. In HI I used one that had specific additives to remove Sulphur Dioxide from the Volcano. I used to maintain a big salt water fish tank and noticed the big differences between what got used there versus what was used in air systems.

Don't know if that helps. Others here may be able to provide more in depth differences as well?

Dave

[Glen Monaghan]

My first attempt was with a batch of stuff reported to be made from coconut husks, pieces that were on the order of 0.5-0.75" cupped/curved shapes, and it was not particularly effective in a 4" thick layer. Probably just too coarse. Better than nothing but insufficient for use when cutting acrylic. I'm currently using GC4x8S, two 4" thick layers, which works quite well for me. The pieces are NOT cylindrical, but generally are approximately 4 mm x 8 mm x 2 mm, with considerable variation in each dimension.

[Gary Hair]

So here is the scenario:
I have a DCS UV printer and print on a lot of anodized aluminum. This requires an adhesion promoter and it is VERY stinky! There is no way to do this outside and it's intolerable inside and takes a while to dissipate even with two window fans drawing it out of the room, that's not really an option in the winter, I'd like to keep the heat inside where it belongs... What I'd like to do is have an air filter running to scrub the smell. I have thought about a range hood with a carbon filter, one over the printer and one over the application area. I thought about a "grow" filter but I'm not sure how well they work. I also thought about building my own filter like the ones in this thread.

My questions are about the effectiveness in general and also how enclosed I would need to keep the printer and application area so that it actually works, no use having the fumes escape around the sides of the filter. Has anyone here done something similar?

Thanks for any suggestions and advice.

[Dan Hintz]

My questions are about the effectiveness in general and also how enclosed I would need to keep the printer and application area so that it actually works, no use having the fumes escape around the sides of the filter. Has anyone here done something similar?

Throw a blanket of plastic over the whole mess, with the intake to the DC/filter at the rear, leaving the front uncovered for access and makeup air. Literally, just a piece of painter's plastic thrown over it all, nothing fancy. The high airflow of the DC should prevent anything from escaping to the side. It's a short-term setup, right?

[Gary Hair]

It's a short-term setup, right?

This is, hopefully, a very long term setup. I run parts almost every day that need to have adhesion promoter. I ended up buying a filter from Costco, it has a hepa filter, a silver nano filter, charcoal filter and something else I can't remember. It was $180 and for the time and materials to build something else I had to give it a shot. If it doesn't work then I'll return it to Costco and continue with the build.

[Brandon Tippets]

First and foremost I want to thank Dan for posting his filter build project here. We recently purchased an Epilog 120 watt Fusion Laser Engraver. Great piece of equipment. Having never owned or operated a laser we quickly found ourselves in need of a way of removing the smell and harmful vapors from our exhaust, which is routed outside. I contacted the company that sold us the laser and they sent me some information on the BOFA filtration units. I couldn’t stomach the replacement filter costs, but it was suggested that I may have to build ‘pre filter’ before the filtration unit anyways. Then I was forwarded a link to this thread.

The company that I am in partial ownership of also has a Komo 508 Mach 1 cnc router. I found an old scrap sheet of a vinyl coated plywood and start doing the layout in ACAD. My goal was to build a box that would sit behind the laser, be easy to access, and to quickly see what was going on inside the unit. We just hooked it up today and the filter is working perfectly.

We vector cut .118" thick clear modified acrylic sheet about 1 to 2 hours a day and our neighbors from nearby shops were starting to complain about the smell. (The modified portion of the acrylic sheet is the additive of rubber to make the sheets/parts stronger. And also makes it very stinky to cut.)

Here are some pics from along the way.


288286


288287288288288289288290

I hope the pics come through okay. this is my first post. Awesome community you guys (and gals) have here. Lots of good information. ;)

[David Somers]

Brandon,

What kind of fan are you using to move the air. Looks like it is located outside that room somewhere?

Dave

[Brandon Tippets]

Brandon,

What kind of fan are you using to move the air. Looks like it is located outside that room somewhere?

Dave

Dave,

Its a 10" in line fan that is rated at 1000CFM. When we bought the laser it came with it. The exhaust behind the laser goes straight up and through the roof (about 20 feet up). The air is being pulled through the filter and is noticeably slower in removing the smoke from the cutting area, but I have a layer about 3" thick of activated charcoal in there now. My next charge I am going to go 2" and see if that is a better balance.

Brandon

[David Somers]

Thanks Brandon. Looks like a nice job! Good luck with the new Epi too!!!

Dave

[Jacob Davalos]

Brandon,

what you need is a blower with more static-pressure "moving power". While inline fans are rated at 1000 CFM, they have very weak static pressure capabilities.

The filter adds a lot of pressure to a system that the relatively weak inline fan fails to overcome. You also have a lot of running duct. You could buy another inline fan and put both inline. While this will not increase CFM, it will increase your static pressure capabilities. Or you could buy a dust collector type of blower and easily triple your static pressure capabilities. When i say triple I mean that your inline fan will do no more than 2.5" WC while a dust collector does 8" WC. If you look up "atmosphere vortex" doing ye ol' googlefu they have a good graph in their showing you the declining CFM relative to the Static Pressure. For a 12" inline fan that at 0" WC pulls through 1000+ CFM, at 1.5" WC it only pulls around 388 CFM. I do not know how to calculate your static pressure, but there is a way - I am sure you have more than 1.5" WC of static pressure with all that piping and 90* bends and the filter.

You do not want to decrease the filtration, as in making your carbon bed 2" instead of 3" - you want to increase the ability to pass air through as thick a carbon bed as is logical for your given application.

Your design is awesome, and with a better blower, you will be good to go I believe.

[Dann Ernstsen]

Could a vacuum cleaner be used as a fan?

[Brandon Tippets]

Brandon,

what you need is a blower with more static-pressure "moving power". While inline fans are rated at 1000 CFM, they have very weak static pressure capabilities.

Your design is awesome, and with a better blower, you will be good to go I believe.


Thanks Jacob,

I have been skeptical of the inline fan since I started designing this unit. It was already in place so I gave it try (and we own it). Having never built a unit like this I wanted to make it sure it worked before I started modifying ducting and fans/blowers, ect. And I am by no means an expert when it comes to air flow so your information above is very much appreciated. I am confident that we aren't done modifying this set up.

It sounds like with a blower it would be easiest to vent back into the shop?

[Jacob Davalos]

Could a vacuum cleaner be used as a fan?

I believe that a vacuum does not have enough CFM (it does not move enough air) to properly vent a laser.


Thanks Jacob,

I have been skeptical of the inline fan since I started designing this unit. It was already in place so I gave it try (and we own it). Having never built a unit like this I wanted to make it sure it worked before I started modifying ducting and fans/blowers, ect. And I am by no means an expert when it comes to air flow so your information above is very much appreciated. I am confident that we aren't done modifying this set up.

It sounds like with a blower it would be easiest to vent back into the shop?

if you are interested in venting back into the shop, you can bring down the inline fan and hook it as close as possible after the filter, so all that ductwork leading to the inline in your roof is no longer an issue (meaning you have less static pressure in your system) so the inline blower may work a bit better.

But I would still suggest a dust collector for the added power needed to suck air through your filter. You can use the dust collector to vent back into the shop if you wish, or you can simply replace the inline you have now and put the dust collector in its place.

PM me and I can show you the 3 options of dust collector I have narrowed down for my filter design.

[Dan Hintz]

I like the acrylic top, Brandon. One problem I see, however, is you're not holding the carbon captive. Once you go with a stronger fan, the negative pressure will begin to float the carbon, reducing its effectiveness.

[Brandon Tippets]

Thanks Dan,

I have been thinking about building a mesh tray to fit inside the filter box that would make it easier to change out the charcoal. I could incorporate a lid into this tray easy enough. I did lay down cheese cloth in between the furnace filter and the charcoal, but it still seems like a might be pain to change out.

I decided to today to go forward with this set up 'as is' until it is time to change out the charcoal. At that point I can look a new blower/fan set up and put the tray I mentioned in place. I am keeping track of how many hours we are running so I can gauge about how long each charge will last.


Thanks again.

Brandon

[John Warren]

Any thoughts on using a car air filter (or something similar) as a pre-filter? Or maybe two (side-by-side to allow more flow-through area, not in series)? Would this restrict airflow too much? Get clogged too quickly?

I'm planning to build a unit like this and thinking through options that could be used as a pre-filter that might be cheaper to replace and not get clogged as quickly as a HEPA (but still have the HEPA at the end to catch the really fine particles).

[Glen Monaghan]

Check into whole-house filters, the 4" thick kind. You can get a wide variety of sizes and ratings to allow desired airflow and filtration level. I use one as my prefilter, followed by several inches of activated charcoal and then the same sized HEPA filter.

[Glenn Chua]

Finally going to give this build a try tomorrow. Thanks Dan !!

Have my Trotec coming in later this week. Trying to decide on fans/blowers. I have an existing 3HP Cyclone, but that will be dedicated to CNC and standard woodworking shop tools as I've read it is not a good idea to throw a laser into the mix.

Wondering if this Vortex S-Line fan off Amazon will work OK?

http://www.amazon.com/gp/product/B00EIRU2YU?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s01

I have someone local that will be selling a lightly used one to me for $75 so figure I would give it a try unless you guys tell me it won't work.

Thanks,

Glenn

[Dan Hintz]

That's a grow fan, meant for very low SP installations. It is not an appropriate fan for fume collection.

[Roy Sanders]

Hi Dan, you're right, "someone will ask," I am slow. If I understood your post, the dirty air comes in the bottom and exits the top. So my question is, do you cover the top of the trash can? I see a black ring around the top, no statement or pic of a top.

So there we are, a question.

Thank you for your generosity. I exit my 40W to outside, but I still get some fume and smoke, think a modified system then go outside will stop that. I use my machine in the basement of my home.

Roy

[Dan Hintz]

do you cover the top of the trash can? I see a black ring around the top, no statement or pic of a top.

I placed the stock trashcan top on and covered all seams with some duct tape. Relatively easy to remove.

[Raphael Weil]

Hey guys,

I was thinking of going with this design as I have access to a CNC: http://lasercuttinglab.com/diy-laser-air-filter/

Can anyone make sense of why they'd want the stack of 4 filters to be activated carbon ones? I assumed the large tray was going to be my diy activated carbon layer (so draw air in the top, filter through stack of furnace filters, then carbon, then one more filter and then vent out the bottom).

Anyway nice design, thought I'd share here to add to the stuff we can use on the site.

[Dan Hintz]

Can anyone make sense of why they'd want the stack of 4 filters to be activated carbon ones? I assumed the large tray was going to be my diy activated carbon layer (so draw air in the top, filter through stack of furnace filters, then carbon, then one more filter and then vent out the bottom).

Each filter is thin, so they need to stack multiples to get enough air "linger" time. If they made a single, thicker filter, it would accomplish the same goal.

[Raphael Weil]

Thanks Dan. Any idea why they want those to be activated carbon though?

I guess my question comes down to not fully understanding the order of the stack given the variance I've seen. I've seen:

-pre-filter (quality furnace filter)
-hepa filter (or diy versions of it)
-carbon filter (again diy)

In this instance it almost looks like

-stack of 4 carbon filters
-big carbon filter
-fiber glass filter



My understanding is that the pre-filter is for the large particles, the hepa is really to eliminate the bulk of the particles, and then the activated carbon is really to clean/deodorize/filter the last portion before venting. Is my understanding correct? In which case having one last filter after the activated carbon is probably pointless?

[Glen Monaghan]

Yep, what Dan said, they are using multiple thin activated charcoal (AC) filters stacked to achieve better odor reduction.

This design is very similar to what I made, only I'm using 16"x19"x4" filters and, rather than routing slots into the sides for trays, I screwed angle aluminum strips to the sides to create shelves that hold the filters. I have four filter "bays", each four inches deep, with the idea that I'd have a 4" thick whole-house filter for prefiltering, a 4" HEPA filter for final filtering of particulates, and either one or two 4" activated carbon trays for odors (especially acrylic). I found that one 4" AC filter was adequate for wood but definitely needed the 8" to control odors from cutting acrylic. Although 8" of AC has proven adequate to control odors for most of my purposes, it wouldn't hurt my feelings to have even a bit more because I definitely noticed the acrylic odor when I did a job that required over two hours of cutting acrylic.

Also, you'll improve efficiency a bit if you provide a large curved airflow deflector in the bottom of the box to smoothly turn the air 90 degrees from the final filter to the exhaust port. Assuming you are exhausting back into the room rather than piping the exhaust somewhere else, replace that dinky circular exhaust opening with as large of a register grate as fits. Likewise, you'll gain a bit of efficiency if you substitute 6" or 8" ductwork for the 4" inlet ducting, along with the appropriately enlarged inlet hole. Finally, with the inlet at the top, it will likely be above your machine's exhaust port and so will have duct coming up and turning 180 degrees to come back down into the top of the stack. Better to move the inlet to the side of the stack with a single large final 90 degree bend in the inlet duct, and then provide a large curved deflector inside the box to turn the air 90 degrees down onto the prefilter. This both provides a larger, less restrictive bend for that final 90 degrees, and also better expands the intake air across the prefilter.

[Glen Monaghan]

Regular filters simply trap chunks. Cheap see-through fiberglass basically only traps fibers and large dust particles. You can buy high MERV filters that have much tinier pores so that they capture smaller particles, but odors and very fine particles such as smoke will still get through. Your first or pre-filter is the cheapest part of the system and should be checked and replaced the most often to maximize the life of the carbon and HEPA filters that follow it.

The activated charcoal (AC) is used primarily to remove odors, although it also will trap some of the particulates. AC is carbon that has been specially treated to create a monstrously high surface area in the form of an immense number of tiny pits and fissures in the carbon's surface. Carbon will naturally bond with odor causing molecules (adsorb them), and AC's huge surface area allows it to adsorb vastly more such molecules than is possible with untreated carbon's comparatively limited surface area However, covering the AC with particulates reduces its ability to adsorb odor so you use a prefilter to trap the bulk of the (larger) particulates before the AC.

The HEPA filter, having the finest structure, is meant to remove the smallest particulates and it will quickly clog up if you don't have good prefiltering. New AC granules will release fine carbon particles when first installed, so some people put the HEPA before the carbon, but I think it's better to have the most expensive part last. Consequently, I try to protect the HEPA filter by blowing clean air through new AC granules before installing them, then temporarily install a HEPA filter I keep for the purpose and run the unit to catch additional carbon dust released by the process of filling and installing the carbon trays. Then I put back the operating HEPA filter and figure it's good to go.

I see no value in putting a fiber glass filter at the end of the stack. That would be the least effective filter and there shouldn't be anything left that it could catch at that point.

[Scott Shepherd]

I'll ask for some technical help, I made one, put the prefilter, then the AC, then the hepa. Ran black acrylic for about 2 days straight, noticed the air was barely moving. Stopped things, looked at it, the hepa filter was black. I weighed the AC and it was essentially the same weight. My guess is that it sucked up the dust from the AC and clogged the hepa filter. How do you stop the charcoal dust from clogging the hepa filter prematurely?

[Glen Monaghan]

I just looked at the design again and realized that there is no fan in the stack, so they probably are using an external fan after the stack, in which case you'd need the duct hole rather than a register grate in order to connect the stack to the fan. I'd still include an airflow deflector inside the stack to smooth the 90 degree transition, and probably a larger duct with final reduction to fan inlet diameter right at the fan. As the design is drawn, there appears to be enough room that you could simply include an inline fan in the stack, which is what I did, placing it at the bottom to keep the center of gravity lower. There's something to be said, though, for using an upflow rather than downflow arrangement, because then you might be able to eliminate a 90 degree bend on the inlet side and the outlet could be straight up through a grate in the top cover, again eliminating a 90 degree bend, plus really big particles could fall to the bottom of the stack without clogging the prefilter.

[Glen Monaghan]

In another post on this thread, I mentioned blowing carbon dust out of the AC before you install it. Then, after installing it, use a "sacrificial" filter for a few minutes while running the unit to clean out additional carbon dust released by the process of installation. The AC shouldn't continue shedding carbon dust during normal operation. Just make sure you don't do anything like washing the AC since impurities in the water will likely ruin the AC's ability to adsorb odors.

[Scott Shepherd]

Thanks Glen, I guess I'll pony up for another filter and give it a try. Worked good for the first day :)

[Raphael Weil]

Yep, what Dan said, they are using multiple thin activated charcoal (AC) filters stacked to achieve better odor reduction.

This design is very similar to what I made, only I'm using 16"x19"x4" filters and, rather than routing slots into the sides for trays, I screwed angle aluminum strips to the sides to create shelves that hold the filters. I have four filter "bays", each four inches deep, with the idea that I'd have a 4" thick whole-house filter for prefiltering, a 4" HEPA filter for final filtering of particulates, and either one or two 4" activated carbon trays for odors (especially acrylic). I found that one 4" AC filter was adequate for wood but definitely needed the 8" to control odors from cutting acrylic. Although 8" of AC has proven adequate to control odors for most of my purposes, it wouldn't hurt my feelings to have even a bit more because I definitely noticed the acrylic odor when I did a job that required over two hours of cutting acrylic.

Also, you'll improve efficiency a bit if you provide a large curved airflow deflector in the bottom of the box to smoothly turn the air 90 degrees from the final filter to the exhaust port. Assuming you are exhausting back into the room rather than piping the exhaust somewhere else, replace that dinky circular exhaust opening with as large of a register grate as fits. Likewise, you'll gain a bit of efficiency if you substitute 6" or 8" ductwork for the 4" inlet ducting, along with the appropriately enlarged inlet hole. Finally, with the inlet at the top, it will likely be above your machine's exhaust port and so will have duct coming up and turning 180 degrees to come back down into the top of the stack. Better to move the inlet to the side of the stack with a single large final 90 degree bend in the inlet duct, and then provide a large curved deflector inside the box to turn the air 90 degrees down onto the prefilter. This both provides a larger, less restrictive bend for that final 90 degrees, and also better expands the intake air across the prefilter.

I'll say this, if this isn't one of the best forums on the internet, I don't know what is. You guys (and not just you Glen) really provide a huge wealth of info.

Glen is your stack order prefilter -> AC -> Hepa? Also your deflector idea sounds amazing. What material did you use for that, some sort of flexible sheet metal or plastic of some kind?


I just looked at the design again and realized that there is no fan in the stack, so they probably are using an external fan after the stack, in which case you'd need the duct hole rather than a register grate in order to connect the stack to the fan. I'd still include an airflow deflector inside the stack to smooth the 90 degree transition, and probably a larger duct with final reduction to fan inlet diameter right at the fan. As the design is drawn, there appears to be enough room that you could simply include an inline fan in the stack, which is what I did, placing it at the bottom to keep the center of gravity lower. There's something to be said, though, for using an upflow rather than downflow arrangement, because then you might be able to eliminate a 90 degree bend on the inlet side and the outlet could be straight up through a grate in the top cover, again eliminating a 90 degree bend, plus really big particles could fall to the bottom of the stack without clogging the prefilter.

In my case I'm going to vent out a window after all the filtering. Might be a bit paranoid, but I think it's a must in my case. The window is 4-5 feet off the ground, so your upflow idea is exponentially more efficient for me. What I don't completely understand is where you place the fan in the upflow version. Does it have to be inline and elevated? Can it still be on the ground before the stack? You can tell I don't know that much about this. I look forward to learning and then one day being the one to help people on here.

[Tony Lenkic]

Many commercial air purifiers install charcol last (after HEPA). There must be a good reason they do that.
My Quatro unit hase them in this sequence:

[Raphael Weil]

Many commercial air purifiers install charcol last (after HEPA). There must be a good reason they do that.
My Quatro unit hase them in this sequence:

Can I ask what you pay a year to maintain/swap out all the filters?

Any chance they put the Hepa before the AC to make it more expensive to maintain? I know that seems shady, but if the Hepa is expensive they probably don't mind having you swap it out a bit more often than is ideal.

[Tony Lenkic]

Less than $ 500.00 / year but that is relevant to usage.

[Glen Monaghan]

Raphael, yes, I settled on prefilter -> AC -> HEPA. Originally, I put the HEPA before the AC but thought it was clogging too quickly, and it's the most expensive section to replace. With HEPA after AC, I find that a light-colored dusting of particulates accumulates over time throughout the 8" of AC. Not sure what it is specifically, but I wonder if it's mostly dust and solidified vapor from acrylic; regardless, that was probably clogging the HEPA filter.

I intended to bend two or three flexible plastic sheets into arcs, roughly quarters of circles, arranged concentrically in the air stream to more smoothly turn the air through 90 degrees. A quick smoke test showed that simply injecting air into the boxy shape and letting it find its own way "around the corner" created turbulence and dead spots. I started by simply bending a suitably sized thin sheet of plastic and slipping it into the space to create a smooth 90 degree arc from the top of the inlet area to the far side of the filter stack. I never did decide on a good way to install and hold a second or third concentric deflector that would divide the air flow and more smoothly direct it across the full face of the prefilter, so it's still just the one deflector on the inlet and one on the outlet.

In general, it's better to have the fan at the end of the run so that the entire system is subject to negative pressure internally, meaning that any leaks will suck in outside air and contain the exhaust products. If the fan is not at the end, then any part of the system downstream of the fan is under positive pressure internally, meaning that any leaks there will allow exhaust products to escape back into your space. That's particularly unpleasant if it happens prior to filtering, less problematic if it happens downstream of the filters. So, for an upflow version with internal fan, you'd ideally have the fan at the top of the stack just prior to the filter's exhaust port so that only filtered air is in the pressurized filter exhaust duct. Just be careful with stability since putting the fan at the top raises the stack's center of gravity. My stack is on casters and, even with the fan near the bottom, it's a bit tippy if you hit a rough spot or something that the wheel won't easily roll over.

[Dan Hintz]

My understanding is that the pre-filter is for the large particles, the hepa is really to eliminate the bulk of the particles, and then the activated carbon is really to clean/deodorize/filter the last portion before venting. Is my understanding correct? In which case having one last filter after the activated carbon is probably pointless?

I would skip the last charcoal filter in favor of a standard filter between the HEPA and charcoal. Other than that, you have it right.


I'll ask for some technical help, I made one, put the prefilter, then the AC, then the hepa. Ran black acrylic for about 2 days straight, noticed the air was barely moving. Stopped things, looked at it, the hepa filter was black. I weighed the AC and it was essentially the same weight. My guess is that it sucked up the dust from the AC and clogged the hepa filter. How do you stop the charcoal dust from clogging the hepa filter prematurely?

I blow out my charcoal before charging the system to prevent just this sort of issue. There's entirely too much dust in a bag of charcoal, so you need to get rid of as much as possible, else it's just in the airstream the first time you turn it on.

[Dan Hintz]

Many commercial air purifiers install charcol last (after HEPA). There must be a good reason they do that.
My Quatro unit hase them in this sequence:

The idea there is to remove all particulate matter from the stream before it hits the charcoal... sounds good, until you realize he HEPA filter gets jammed up pretty good with particulates that can't be easily removed. Charcoal gets replaced and it's cheaper than a good HEPA, so I now prefer that filter order. To be fair, I ended up ith that order due to poor planning on my part during the original design, and my intention was to "fix" the problem on my next rebuild. After some serious use, however, I saw what was happening and decided to leave well enough alone.

[Zach Browning]

I'm looking to build a similar stacked filter for my laser, which is going to be located in an area where external venting is not a possibility. I also need it to be as quiet as possible, so a dust collector motor is not going to work. I saw another thread where they used two vacuum motors in a sound dampened box, but the last post on that thread was over a year ago. I PM'd the OP of that thread about what model motor he used, but haven't heard anything back. What kind of CFM should I be looking for? Most vacuum motors I've looked at push around 90-100 CFM, but does that scale so that two motors running at half speed would push the same 90-100?

I also found this http://www.supplyhouse.com/Fantech-FG8XL-FG-Series-Round-Inline-Exhaust-Fan-8-Duct-502-CFM
The spec sheet says it does ~500 CFM at 0" SP, but drops to ~100 at 2" SP, not sure what kind of restriction the filter would apply.

All this airflow terminology is new to me, so any input would be greatly appreciated.

[Dan Hintz]

I'm looking to build a similar stacked filter for my laser, which is going to be located in an area where external venting is not a possibility. I also need it to be as quiet as possible, so a dust collector motor is not going to work. I saw another thread where they used two vacuum motors in a sound dampened box, but the last post on that thread was over a year ago. I PM'd the OP of that thread about what model motor he used, but haven't heard anything back. What kind of CFM should I be looking for? Most vacuum motors I've looked at push around 90-100 CFM, but does that scale so that two motors running at half speed would push the same 90-100?

I also found this http://www.supplyhouse.com/Fantech-FG8XL-FG-Series-Round-Inline-Exhaust-Fan-8-Duct-502-CFM
The spec sheet says it does ~500 CFM at 0" SP, but drops to ~100 at 2" SP, not sure what kind of restriction the filter would apply.

All this airflow terminology is new to me, so any input would be greatly appreciated.

Impeller speed versus airflow is much closer to a square law than linear... and combining two motors never works the way people intend (certainly not double the airflow). CFM at 0 SP is a worthless figure as you will never have 0 SP. Expect at least several inches of water SP in your system, and 100 CFM just isn't going to clear the cabinet very fast (lots of smoke will linger).

[Raphael Weil]

Hi all,

I was wondering if I could get one last check up on design, I'm picking my blower now.

My design has a first right angle out of the laser to my filter stack 2-3 feet away. Another right angle into the stack with a deflector to help redirect air upwards (my stack is bottom to top airflow). Then it runs through 4 feet of pre filters/filters/carbon/hepa up into the blower. So this is where I'm currently stuck. Based on everything I've read, it sounds like an 8" blower in the 600-700 cfm range is going to be what gets the job done (I'm assuming louder than I'd like even sound proofed). So my question is, if I am using an 8" blower, should I stick to 8" size throughout the design and convert from 8" to 4" at the laser? Am I negating the benefit of the 8" duct if I convert to 6" at the area that leads to the laser? I don't actually know if 8" -> 4" is a connector that's out there. I had originally planned on 6" to 4".

I have my eye on this, just not sure if it's total overkill, and if I could somehow pull this off with a quieter 6" (based on research on here, there is no 6" blower with enough cfm's)

http://www.hydroshop.ca/en/climate-control/ventilation/air-extractors/atmosphere-vortex-1039.html

[Glen Monaghan]

The smallest opening or duct in the system will be something of a limiting factor, but a duct is more limiting than an opening of the same diameter (due in large part to friction along the duct wall). Ideally, your duct work will be at least as large in diameter as your fan, so 8" duct will be better than 6" duct and much better than 4" duct. Although it would be better to have a smoothly transitioning 4" to 8" adapter (or possibly 4" to 6" immediately followed by 6" to 8" if that were easier for you), a simple step adapter really won't be noticeably worse in this application. I originally created my system with an 8" fan that looks similar to the one you referenced and so used 8" duct between the laser and filter stack. (That said, I wasn't happy with the air flow through my prefilter, 8" AC stack, and HEPA filter and so have since replaced the 8" fan with a 12", the largest that fits my layout.) Where the 8" duct meets the laser's 4" port, I closed the end of the 8" duct with an 8" duct tee cap in the center of which I had cut a 4" hole to fit the laser port. Sealed all the joints with aluminum duct tape. Alternatively you could cut an arc of aluminum flashing and fashion a 4" to 8" funnel shape for what should be a more efficient home made adapter.

[Raphael Weil]

The smallest opening or duct in the system will be something of a limiting factor, but a duct is more limiting than an opening of the same diameter (due in large part to friction along the duct wall). Ideally, your duct work will be at least as large in diameter as your fan, so 8" duct will be better than 6" duct and much better than 4" duct. Although it would be better to have a smoothly transitioning 4" to 8" adapter (or possibly 4" to 6" immediately followed by 6" to 8" if that were easier for you), a simple step adapter really won't be noticeably worse in this application. I originally created my system with an 8" fan that looks similar to the one you referenced and so used 8" duct between the laser and filter stack. (That said, I wasn't happy with the air flow through my prefilter, 8" AC stack, and HEPA filter and so have since replaced the 8" fan with a 12", the largest that fits my layout.) Where the 8" duct meets the laser's 4" port, I closed the end of the 8" duct with an 8" duct tee cap in the center of which I had cut a 4" hole to fit the laser port. Sealed all the joints with aluminum duct tape. Alternatively you could cut an arc of aluminum flashing and fashion a 4" to 8" funnel shape for what should be a more efficient home made adapter.

Wow how many CFM was the 8" fan you used? That makes me a bit nervous. This 10" beast allegedly runs at 52db and cranks out 800 cfm. I'd hope to manage to still draw 450 by the time it makes it to the laser. Maybe wishful thinking.

http://www.aftproducts.com/Centrifugal-CF-10-Model-800-CFM.item

[Dan Hintz]

I can't tell people this enough... stop looking at hydroponics-style blowers. They're meant for practically 0" of SP and only work in rare cases (e.g., short paths). You need a dust collector style of fan, one that has a reasonable SP at a reasonable CFM.

[Zach Browning]

I can't tell people this enough... stop looking at hydroponics-style blowers. They're meant for practically 0" of SP and only work in rare cases (e.g., short paths). You need a dust collector style of fan, one that has a reasonable SP at a reasonable CFM.

It would be nice to know what a "reasonable SP at a reasonable CFM" would be, i.e rough numbers to look at. A lot of us have no experience with airflow, so a simple guideline to look for would really help.

[Raphael Weil]

I can't tell people this enough... stop looking at hydroponics-style blowers. They're meant for practically 0" of SP and only work in rare cases (e.g., short paths). You need a dust collector style of fan, one that has a reasonable SP at a reasonable CFM.

Thanks Dan, I had somehow missed that in all the thread reading on here. Any brands you like in the 10" variety?

[Glen Monaghan]

Wow how many CFM was the 8" fan you used? That makes me a bit nervous. This 10" beast allegedly runs at 52db and cranks out 800 cfm. I'd hope to manage to still draw 450 by the time it makes it to the laser. Maybe wishful thinking.


Hah, surprisingly I was able to locate the specs given for the fans I have, although they are incompletely specified, probably not really something you can use for apples to apples comparison against your fan:



Spec:


**Flange( optional )
4"
6"
8"
10"
12.40" 315mm


Voltage
110-120V


Power
113W
115W
195W
240W
285W


Airflow Rate
190 CFM
440 CFM
720 CFM
780 CFM
1210 CFM


Revolutions
2890 RPM
2910 RPM
2650 RPM
2620 RPM
2500 RPM


Current Flow
0.95 Amps
0.97 Amps
1.65 Amps
2.1Amps
2.45 Amps


Working Environment Temperature
-20 to 40 degrees Celsius


Motor Insulation Class
F (Much Safer, can endure 155 degrees Celsius)


Noise
51db
52db
55db
52db
55db


Overall Dimension aprox
11"x8"x13"
12"x8"x14"
15-3/4"x8-1/2"x16-1/2"
15-3/4"x8-1/2"x16"
17"x16"x10



My 8" fan was rated at 720 CFM (almost certainly at 0" of water) while the 12" is supposed to be 1210 CFM (about 1.68x more than the 8" rating). I would like to measure the actual CFM, in part to help determine when the filters should be replaced, but haven't looked into what's a reasonable way to do that; will probably just settle on measuring velocity at some point in the system.

Anyway, changing to the 12" fan definitely improved airflow, and the noise is about the same as with the 8" fan (in part because it's spinning slower). The fan and filters are inside a 3/4" thick composite wood/melamine case next to the laser, and you can carry on a conversation or phone call while standing in front of the laser, albeit with some hindrance. I can even hear the "super silent" fans on the laser ramping up and down according to tube temperatures, whereas I never heard them at all over the racket of the HF unit I previously used.

Another nice thing about the larger fan diameter is that it more closely matches the size of my filters, which are 16"x19", so the airflow distribution through the filters is more even than with the 8" fan.

[Raphael Weil]

It would be nice to know what a "reasonable SP at a reasonable CFM" would be, i.e rough numbers to look at. A lot of us have no experience with airflow, so a simple guideline to look for would really help.

For the Speedy 300 I was told Minimum 360, ideal 500 cfm





My 8" fan was rated at 720 CFM (almost certainly at 0" of water) while the 12" is supposed to be 1210 CFM (about 1.68x more than the 8" rating). I would like to measure the actual CFM, in part to help determine when the filters should be replaced, but haven't looked into what's a reasonable way to do that; will probably just settle on measuring velocity at some point in the system.



May I ask what brand that is?

Dan is this still considered a hydroponic style blower still? In Canada these are sold as industrial inline blowers. http://www.homedepot.ca/wcsstore/HomeDepotCanada/images/catalog/VORTEXSPECS.pdf

They move a ton of air, the one I'm eyeing is 820 CFM out of a 12" end. I'm just not clear on the difference between that and a dust collector style fan. I'm running through something like 6 filters before it ever hits this fan. I'm in starting at 1210 CFM and I lose 60% of that by the time I make it to the laser, I'm still happy with that.

The harbour freight model weighing in at over 100 lbs is a real killer for my design right now. I'd have to totally scrap my current plan if the fan is to weight that much.

[Glen Monaghan]

May I ask what brand that is?
A sticker on it says MTN


They move a ton of air, the one I'm eyeing is 820 CFM out of a 12" end. I'm just not clear on the difference between that and a dust collector style fan. I'm running through something like 6 filters before it ever hits this fan. I'm in starting at 1210 CFM and I lose 60% of that by the time I make it to the laser, I'm still happy with that.

Maybe a ton of air under no load, but you have to find out how much it will move when loaded with the pressure drops through your ducts, elbows, filters, etc. It can be difficult to obtain CFM vs SP curves for different fans, but an example of the relationship between CFM and SP for a reasonably typical inline fan with 12" inlet/outlet might be:
SP CFM
0.0" 1140
.125 1013
.25 882
.375 762
.5 688
.75 567
1.0 498
1.25 442
1.5 388

So you can see they typically have a steep loss of CFM as the SP increases. It's a bit like a car running in overdrive... running down wind on a level road (low dynamic and static pressures) the car goes fast (high CFM) but, as you try to buck increasing faster head winds (high dynamic pressure) or especially try climbing increasingly steeper hills (high static pressure), the car's limited torque in overdrive causes it to quickly lose speed (drastically reduced CFM).

If you can figure out the losses in each part of your system, you can match that to a suitable fan. The problem is actually determining out those losses, so most people just try one or more fans and empirically determine what works and what doesn't. If you choose a ventilation type fan for the lower noise characteristics they typically provide, you have to be very careful about minimizing restrictions that quickly cut CFMs. The alternative is to go with a fan that is designed to operate at equal or higher SP than you expect to require for your system (again referring to the car analogy, this is similar to running around in 1st or maybe 2nd gear... you can go up hill and into head winds at pretty close to the same speed you go on flat ground, but the engine/transmission noise will be significantly louder than in overdrive, and increasingly more so as you try to go faster (move more CFM)

[Raphael Weil]

A sticker on it says MTN



Maybe a ton of air under no load, but you have to find out how much it will move when loaded with the pressure drops through your ducts, elbows, filters, etc. It can be difficult to obtain CFM vs SP curves for different fans, but an example of the relationship between CFM and SP for a reasonably typical inline fan with 12" inlet/outlet might be:
SP CFM
0.0" 1140
.125 1013
.25 882
.375 762
.5 688
.75 567
1.0 498
1.25 442
1.5 388

So you can see they typically have a steep loss of CFM as the SP increases. It's a bit like a car running in overdrive... running down wind on a level road (low dynamic and static pressures) the car goes fast (high CFM) but, as you try to buck increasing faster head winds (high dynamic pressure) or especially try climbing increasingly steeper hills (high static pressure), the car's limited torque in overdrive causes it to quickly lose speed (drastically reduced CFM).

If you can figure out the losses in each part of your system, you can match that to a suitable fan. The problem is actually determining out those losses, so most people just try one or more fans and empirically determine what works and what doesn't. If you choose a ventilation type fan for the lower noise characteristics they typically provide, you have to be very careful about minimizing restrictions that quickly cut CFMs. The alternative is to go with a fan that is designed to operate at equal or higher SP than you expect to require for your system (again referring to the car analogy, this is similar to running around in 1st or maybe 2nd gear... you can go up hill and into head winds at pretty close to the same speed you go on flat ground, but the engine/transmission noise will be significantly louder than in overdrive, and increasingly more so as you try to go faster (move more CFM)

Ah that's super helpful. I also just found this from here (https://www.cincinnatifan.com/how-to-select-fan.htm) (I'm allowed to link that right? if not sorry mods delete)

Centrifugal fans or blowers use one of seven types of wheels that are enclosed in a scroll shaped housing. The air enters the fan wheel through the housing inlet, turns 90 degrees and is accelerated radially and exits the fan housing. Centrifugal fans are typically used for lower flows and higher pressures.
Axial fans use a propeller, having two or more blades, to move air in an axial direction through a cylindrical housing or formed orifice panel. Axial fans are typically used for higher flows and lower pressures. Do not use an axial fan to convey material.

[Dan Hintz]

If the given spec is at 0" of water, move on to another fan... those are designed for large volumes of air at little to no pressure. Once you've closed your cabinet door, run 20' of piping through multiple 90 degree bends, etc., you will need a decent amount of SP to pull that restricted air through. A reasonable amount for a desktop machine would be several hundred CFM @ 2-3" of SP. For larger units, like a 24"x36" bed, I would raise that to 500CFM+ @ 3-5" SP. These are all rough numbers, of course, but they give you an idea of what to shoot for. I got away with the red Harbor Freight unit with my 18"x24" ULS system... once it pulled through my home-made fume extractor, I would call it adequate, but not awesome.

[Raphael Weil]

If the given spec is at 0" of water, move on to another fan... those are designed for large volumes of air at little to no pressure. Once you've closed your cabinet door, run 20' of piping through multiple 90 degree bends, etc., you will need a decent amount of SP to pull that restricted air through. A reasonable amount for a desktop machine would be several hundred CFM @ 2-3" of SP. For larger units, like a 24"x36" bed, I would raise that to 500CFM+ @ 3-5" SP. These are all rough numbers, of course, but they give you an idea of what to shoot for. I got away with the red Harbor Freight unit with my 18"x24" ULS system... once it pulled through my home-made fume extractor, I would call it adequate, but not awesome.

That's awesome guidance Dan, thanks. I spoke to an aerospace engineer today who actually uses the Vortex ones (the grow room axial), and he mentioned that Vortex specifically does make some axial models designed for far more static pressure that haul through all manner of filters etc... So I'm going to get Vortex to send me some specs to see how they hold up. I do understand why the other typical axial models don't do the job now. Thanks for all the instruction guys :)

The reason I'm so keen on trying to make one of these work is the weight and the wattage. If I can deal with a 30-40 lb axial and it doesn't need a 20A circuit, it's going to make my life way easier. I already have a dedicated 20A for the laser itself.

[Raphael Weil]

I found this interesting, vortex got back to me about if their axials could do the job. Their estimates on the static pressure based on my design (3 ninety degree turns, 9 feet of run, my filters)

The pressure drop for the for the ducting and the 3 90 elbow in 10’’ ducting is 0.08’’ WC
The pressure drop for the carbon filter is between 0.5 ‘’ WC to 0.75’’ WC depending on the brand
The Pressure drop for all other accessories are unowned but I would put at least 0.125’’ W.C.

For a total of0.955’’ WC


That struct me as a bit low,but I think it sounds to be under 2" nevertheless.