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Offlineoderus urungus
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Laminar flow hood build (pics) and a couple ?'s
    #11420469 - 11/09/09 07:15 PM (11 years, 5 months ago)

Here's some pictures of a laminar flow hood build.

"These are some of the supplies that I needed.



I have a 24"x24"x11.5" hepa filter, I will make my box a 24" square. This will give me a plenum that is as deep as the filter is wide, plus with a 24" box I can get away with one sheet of plywood. I cut my bottom piece of ply 24x24, then I glued the middle of the filter and used silicone around the edges to attach filter to the plywood. Once the glue drys it never coming out of there. Make sure you have a solid bead of glue and silicone so air has no spots to get through.





Then I cut my sides 24x24 3/4" tall to cover the bottom piece of ply. Glued and silicone, then nailed into place. You can use screws if you want.





Repeat for the other side.



Then I cut my top 24"x25 1/2" to cover up the sides. I cut in my vent hole before I installed it so that I didn't have to cut above my HEPA. I cut the hole big enough to fit one of my pre-filters which is just a air filter for a car that just happened to fit my exhaust for my blower.(I had to cut 1/4" off the rubber). I cut the hole to fit just the paper of the filter and the rubber went up against the ply on the outside. I also siliconed it into place.




Then I mounted the motor. You can look at my other post to see how to wire the motor. THANKS TO RR!!!!:thumbup: I ended up using the high speed on my blower.

Here is a pic of the inside of the blower, the rubber fits up against the rim of the blower nice and tight. I even put a bead of silicone on the inside edge of the rubber to the blower.






Here is a pic of the cleats getting installed. I glued them and then siliconed after they were installed. They hold the filter in place and stop air from getting through the edges.




Then I installed another pre-filter, it is a 24x24 furnace filter. I also cleated that into place.



Then I installed the back. This is where I realized that I fucked up. I should have put the back on before the motor and auto pre-filter. Now I cant silicone the edges. I just glued the shit out of the ply before I put it together. I glued all edges before I nailed.


Then all I had to do was finish wiring the motor and I installed another pre-filter to the motor. I do have covers for my eletrical boxes I am just messing with some stuff. I put the switch on ther so I can mount my bendable light to the box.





Here's a pic of it in action



I still have a piece of trim I want to cut for the front then attach hinges to a piece of white melemine plywood that I can clean and use as a work space and then close it to protect the filter. I want to polyurathane the whole box or paint it eggshell white so I can wipe down the plywood for cleaning.
Total costs
Blower-free, I scrapped it from a furnace that was going to the garbage, also you can also call HVAC guys and ask for old blowers.
HEPA-$80 from Ebay
Plywood-$15
Plug/boxes/cord end/outlet-$15
Fasteners- already had
pre-filters-$17
Glue/silicone-$10
total= about $140-150.
Not getting contaim floating around= PRICELESS
The one problem I am having is when I move the lighter around I have found a spot in the the dead center of the filter that does not seem to have as good a flow but its just a 4"-6" diameter circle. The lighter kinda flickers and stands up a little, I wonder if I need to take a pre-filter off (but you can see in the last pic how much shit I already have on the pre-filter) or if I should have cut off the plenum a little. What if I put 45 degree angles in the sharp corners. Does anyone have any suggestions or do I need to even worry about it if the center is surrounded by good flow and its above where I am working, kinda. I also wonder if I can put a shelf about 10-12" down from the top, or would this mess up the flow. I would only do this if I can get my flow a little better. I think a shelf would mess up the flow and end up dropping contaims on my lower surface. Anyone ever try putting a shelf in front of a flow hood for extra space?


--------------------
In the name of GWAR, in the name of love
In the name of the blood dripping out of the sun
I call out your God, till before me he stands
But don't send me Jesus, he's only a man



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OfflineRogerRabbitM
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: oderus urungus]
    #11420691 - 11/09/09 07:46 PM (11 years, 5 months ago)

The pre-filter(s) should be on the intake, not the exhaust side of your motor.  At the very least, I'd get rid of the automotive air filter and/or move it to the intake.  You want the exhaust side of your blower to pressurize the plenum in order to get laminar flow.  The furnace filter is not laminar flow, so that might be what's causing the dead spot in the middle.  Try getting rid of them and see if the flow becomes even all over.
RR


--------------------
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"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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Offlineoderus urungus
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: RogerRabbit]
    #11424519 - 11/10/09 09:28 AM (11 years, 5 months ago)

Thanks RR,

  I took off the auto filter first and immediately lost any kinda laminar flow I had. Then I took off the furnace filter and put it back together, now there is too much flow. I cant even put a lighter flame near the area. I tried to block off the intake with cardboard and it still sucks so much air in by the motor that its still too high. I have it on low right now with the red wire. How do you put a pre-filter on the motor side of the intake? I wanted to box in the motor but I am worried about the motor overheating. I have enough plywood that I can do a 24" box around the motor then put in the auto filter or furnace filter. I would think the auto filter would give more resistance but it might be too small of a hole and let the motor overheat. I think a furnace filter would not have enough resistance but it would give good flow the motor so it wont overheat. I read that some people use two auto filter as pre-filters. Thanks again for your help.


--------------------
In the name of GWAR, in the name of love
In the name of the blood dripping out of the sun
I call out your God, till before me he stands
But don't send me Jesus, he's only a man



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OfflineRogerRabbitM
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: oderus urungus]
    #11424684 - 11/10/09 10:16 AM (11 years, 5 months ago)

I'd keep the motor on the outside.  You can see the ghetto method below where I attached the prefilter to the motor with duct tape.

For a 4 square foot filter, you want roughly 500 cfm @ 1" of static pressure.  You can make a homemade manometer easily from clear plastic tubing to test your static pressure.  Here's another one.  All you need is a few feet of plastic tubing and a hole in the side of your case to the plenum to stick the tubing into.  You can make a patch for when you're not testing.

If your motor is still blowing too hard on low, block off more of the intake or get a motor speed controller to slow it down a bit more.  It sounds like your motor is too large for the application.
RR


--------------------
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semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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Offlineoderus urungus
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: RogerRabbit]
    #11427006 - 11/10/09 05:05 PM (11 years, 5 months ago)

Well I took the big motor off and put on a smaller one. The fan is a 10" circle x 10" wide. I cant see the RPM's without taking the motor apart. I am guessing its about 400-600 cfm. It still seems too big of a motor. (on low speed)It wants to blow out the flame on the lighter and it does sometimes. If I put on a motor speed controller will it go lower then low (if that makes sense to you)? I have a sheet of filter that I triple layered and taped to the blower then a furnace filter I cut and made 2 circles out of and taped both of them to the filter. Then I took another piece of the furnace filter and put it over the motor (just let the suction hold it into place) but I still think there is too much flow and if I try to block the intake it just sucks more air in by the motor. I put a piece of cardboard over the intake and it did not help the lighter flame. I still have not heard if you can put a shelf in front of a flow hood either. Thanks so much for your help RR you are the man!:thumbup:


--------------------
In the name of GWAR, in the name of love
In the name of the blood dripping out of the sun
I call out your God, till before me he stands
But don't send me Jesus, he's only a man



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OfflineMigraine
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: oderus urungus]
    #11428846 - 11/10/09 10:43 PM (11 years, 5 months ago)

You are looking for airflow of 100 to 200 ft/min coming off the face of the filter.

Find the frontal area of the filter's face in square inches.  Divide that by 144 to give you square ft.  Multiple that by your wanted air flow in ft/sec (100 to 200) and that will give you the minimum CFM required - NOT TAKING Static loss into account.

Your filter is 24x24.

Calculate to the high side of air flow (200 fpm) so you still have headroom as the filter fills up.

min CFM = ((24*24)/144)*200) = 800 CFM.

You need a blower that will supply a minimum of 800 CFM at 1 inch of static pressure.

A lot of squirrel cage blowers are driven by motor that do not lend them self to being speed controlled.

I used a Vortex inline fan.  This type of fan is great for a flow hood application.  The speed motor can be easily controlled by a "Router Speed Control" from Harbor Freight.

If you install a fan with 800 to 900 CFM and a speed control, you can slow it down to provide the 100 ft/min air flow for the hood with head room to crank up the motor speed as the filter fills up.

Good Luck.


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Re: Laminar flow hood build (pics) and a couple ?'s [Re: Migraine]
    #11429342 - 11/10/09 11:41 PM (11 years, 5 months ago)

800 cfm is too much for a 4 square foot filter.  I like about 100 feet per minute leaving the face, so that requires 400 cfm in a perfect world.  However, add 20% or so for friction, prefilter, etc., and a 500 cfm blower would be about perfect.

Try restricting the intake with a piece of cardboard with only a 1" hole drilled in the middle.  Gradually increase the hole size until you get the flow you want.
RR


--------------------
Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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OfflineMigraine
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: Migraine]
    #11429598 - 11/11/09 12:15 AM (11 years, 5 months ago)

RR.

I humbly agree and disagree.

I like 100 ft/min also - so I agree with your 500.  I suggested the CFM required to achieve the 200 so that 2 years from now when the filter is becoming clogged - the max'ed out 500 cfm blower may only be capable of suppling 70 ft/min through the filter.  With the extra design margin and the use of a speed control, you have the ability over time to increase the CFM output of the fan to compensate for the added restriction associated with the filter.


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OfflinePuma
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Re: Laminar flow hood build (pics) and a couple ?'s [Re: Migraine]
    #11429969 - 11/11/09 01:11 AM (11 years, 5 months ago)

Nice one! I recently built a flow hood using virtually the same HEPA filter and a very similar design. I had to dampen the blower intake a fair bit to get it down to 100 CFM (as RR pointed out to me, a lighter flame should be at a 45 - 90 degree slant at the working face of the filter). I agree that an overpowered filter is preferable because then you can dampen it by using extra prefilters, switching them as they become soiled and thus extending the life of your HEPA filter. I didn't end up with a dead spot, however -- have you solved that yet?

My thoughts on a shelf is that it's a bad ideal, as anything placed in front of the laminar flow disrupts the smooth linear movement of air, creating an eddy like a rock in a river. Why mess with the laminar flow you've worked so hard to achieve? On the other hand, maybe a thin metal shelf wouldn't be so bad. The best way to know I guess would be to do the open petri dish agar test...


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Edited by Puma (11/12/09 11:26 PM)


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Shop: PhytoExtractum Maeng Da Thai Kratom Leaf Powder   Original Sensible Seeds Autoflowering Cannabis Seeds   Kraken Kratom Red Vein Kratom   Unfolding Nature Unfolding Nature: Being in the Implicate Order   Amazon Agar, HEPA Filter, Laminar Flow Hood, Petri Dish

Mushrooms, Mycology and Psychedelics >> Advanced Mycology

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