Sciencemadness Discussion Board

Fume Hood Construction

careysub - 4-7-2016 at 22:12

Working on the design for my own fume hood.

My main reason for posting today is to ask Magpie how his window frame is attached to his fume hood.

I want to copy his approach of using a standard vinyl window for the fume hood face, but looking at the installation instructions for the Jeld-Wen products at Home Depot, they apparently have a "nailing fin" attached to the outside of the frame, and expect you to nail it into a wood frame surrounding the window frame. Undesirable for several reasons - minimizing wood used in construction (I want it to be nearly all metal), adds extra width to the unit, etc.

Magpie has somehow mounted it flush to the (wood?) frame directly behind the window frame.

How he do that?

My own design concept is to make a free standing unit that can be taken apart for moving. I want to base it on this product, which is reasonably priced square aluminum framing that bolts together in modular fashion (80/20 Inc. Ready Tube):
https://8020.net/catalog/category/view/s/shop/id/837/?cat=38...

Painted galvanized steel sheet (cheap, strong) will be screwed on to the sides to make the enclosure.

The 1.5" frame makes a convenient baffle set-up. Attach steel to the outside back, then baffle steel sheet to the inside, using the 1.5" gap as the draft space. Install frame tubes with connector inserts at suitable locations, and you have nice attachment points for mounting stuff on the frame inside the box.

I am puzzling out how a window frame can be best mounted on a Ready Tube frame.

My idea for a work surface (a removable table surface that can be inserted through the window and rests on the frame) is to use bar-top epoxy resin: the stuff that make hard transparent surfaces. Attach aluminum edging to a plywood table, and pour the resin to make the work surface. Epoxy does not dissolve in any solvent, and you can always re-pour a new layer to refresh the surface if desired. It also has the nice property of being self-leveling - it always makes a perfectly flat, level surface.


Magpie - 5-7-2016 at 08:32

Quote: Originally posted by careysub  
Working on the design for my own fume hood.

My main reason for posting today is to ask Magpie how his window frame is attached to his fume hood.

I want to copy his approach of using a standard vinyl window for the fume hood face, but looking at the installation instructions for the Jeld-Wen products at Home Depot, they apparently have a "nailing fin" attached to the outside of the frame, and expect you to nail it into a wood frame surrounding the window frame. Undesirable for several reasons - minimizing wood used in construction (I want it to be nearly all metal), adds extra width to the unit, etc.

Magpie has somehow mounted it flush to the (wood?) frame directly behind the window frame.

How he do that?


Glad to give some details: ;)

The support frame for my Jeld-Wen window is composed of 2x4's on end, so to speak. This does add an extra 1.75" of width on each side.

The window fins are nailed to the 2x4's on the front side. On the back side my 14 ga aluminum hood fins are likewise nailed to these same 2x4's. On the front side the window fins are covered by a molding of 1.75" width, as a cover, and for cosmetic reasons. The inner edge of the moulding strips are sealed to the window using a bead of caulk.

I'm sure you know this but one shouldn't obsess about small leakage gaps and non-perfect seals as small inflows of air are inconsequential.

Will you use a single pane constant flow design?

[Edited on 5-7-2016 by Magpie]

hood construction.bmp - 703kB

[Edited on 5-7-2016 by Magpie]

careysub - 5-7-2016 at 15:35

Thanks! I want to build on your success.

Quote: Originally posted by Magpie  

I'm sure you know this but one shouldn't obsess about small leakage gaps and non-perfect seals as small inflows of air are inconsequential.

Will you use a single pane constant flow design?


Taking the second comment (the question) first:
No, I intend for the sash height to modulate the inflow velocity.

And:
Yes, I do know that. In fact I was contemplating having a non-windowed intake gap at the bottom (between the table and the frame on the side) to create a background inflow rate to reduce the degree of dependence on in-flow with sash height (it would lift an aluminum strip that would drop down blocking the intake when the fan is off). Not sure if I will pursue this idea.

Magpie - 5-7-2016 at 16:10

I know some or most of the professional hoods have a bypass located on top and/or possibly under the hood opening. These are redundant and an over-complication if a constant flow design (like mine) is used.

I'm trying to muzzle myself but I can't over-emphasize the benefits of the constant flow design:

1. Air velocity is constant no matter the sash position. Therefore your fumes will be carried out and your bunsen burner will not be blown out. A closed window allows no airflow and the fumes will just sit there.

2. A blower has an optimum air flow for best performance. The constant flow design provides this unvarying optimum flow no matter the sash position.

3. For maximum body/face protection pull the single window all or most of the way down. Airflow is unchanged as it is now all or mostly all going in over the window above your head.

I don't think I've ever convinced anybody yet but since you are making some effort and expense to do it right I thought I'd try one more time. :D

careysub - 5-7-2016 at 16:14

Well I could always change it to a constant flow design later simply by knocking out the top pane...

Speaking of protection - do you have a film on your glass (or else a special glass) to prevent fragmentation in an explosion?


[Edited on 6-7-2016 by careysub]

Magpie - 5-7-2016 at 16:15

Right....;)

CharlieA - 5-7-2016 at 16:49

from careysub:
I want to copy his approach of using a standard vinyl window



You might want to look into using polycarbonate sheet instead of vinyl. You could make the window from yourself or use the PC sheet to re-glaze an existing window. PC is much safer than a glass window.

Magpie - 5-7-2016 at 17:07

Quote: Originally posted by careysub  

Speaking of protection - do you have a film on your glass (or else a special glass) to prevent fragmentation in an explosion?


The sash is double-pane tempered glass per my order from Home Depot. There's no special covering on the glass.

careysub - 5-7-2016 at 17:38

I am considering this fan, in lieu of a belt driven fan:
http://www.mcmaster.com/#19135k67/=135nfas

It has a "totally enclosed motor", aluminum blades, and a plastic body. An in-line fan is much more convenient for me space-wise, and this is significantly cheaper to boot.


Magpie - 5-7-2016 at 21:33

Whatever fan you select it must be able to deliver enough flow to provide 1.0-1.5 fps face velocity at your hood opening. It also must be corrosion resistant and spark free in the exhausted air environment.

If you don't have a constant flow design your face velocity is going to vary all over the place, depending on sash position.

My squirrel cage fan blades are epoxy coated steel. I have never inspected my fan internals since installation (11 yrs ago). I just know that the fan still works well.

3/8" SP looks a little weak to me but I don't know the diameter, shape, and length of your ducting. My fan delivers 400-500 cfm at 3/4" SP.

All of this guidance I have repeated several times in the hood threads to various posters. In the end I find that people just do whatever they had in mind in the first place. Everybody has their own space and money constraints. As garage chemist said: "any ventilation is better than none." :D

[Edited on 6-7-2016 by Magpie]

careysub - 6-7-2016 at 06:55

I need 285 CFM for 1 FPS with the sash wide open on a 36"x48" window.

The total distance from the 8" x 12" trunk duct plenum on top of the fume hood (I intend to use a slot along the top for extraction) using 8" ducting is 4 feet to the garage side vent with one 90 degree bend. I calculate a pressure drop of 0.01" (rounding up). So 310 CFM at 0.375" looks good.

OTOH, I was also looking at this, and using a carbon filter (static pressure drop 0.5") to reduce odoriferous releases:
https://www.amazon.com/Can-Fan-Inline-6-Inch-Minute/dp/B004C...
which delivers 283 CFM with a filter.

At $100 it could be considered a replaceable item if it fails from corrosion.

Having a carbon filter upstream may provide some protection (I know they do not do much with acid gases), and I would endeavor not to put lots of corrosive gases through it (the hood is after all primarily a safety system, not a chemical disposal system). Proper experiment set-up should try to capture and neutralize such releases, and I do have the option of doing some simple operations outside if corrosive release seems unavoidable.

Getting an indutrial type blower rated as "explosion proof" (is "spark resistant" a suitable substitute?) is a problem, it looks like it multiplies the cost by about 10, pushing it into the "unaffordable" column, and makes units delivering adequate static pressure in my size very hard to find at any price, and many of the units offered in this category are extremely loud.

The only possibly suitable units from McMaster-Carr are $860-$1000 and are 65-70 dB (I would be standing just a few feet away).

Someone on this thread suggest boat bilge blowers. They are "ignition protected, spark proof", and are amazingly cheap - $25-40.

For example this one I can find a static pressure curve for (see attached):
http://www.westmarine.com/buy/shurflo--yellowtail-marine-blo...
Even at 0.5" static pressure the 220 CFM $38 unit delivers about 165 CFM. I would need two of these 4" units, but they are small and I could mount them inside a foam/fiberglass plenum box (helps muffle them too). Requires a 13.6 V, 10.4 A power supply, but I need to drive LED lighting anyway. Looks like maybe the way to go. With an encased motor and a nylon blade sounds like it is corrosion-proof also.


Attachment: 911-723-C.pdf (177kB)
This file has been downloaded 1435 times

[Edited on 6-7-2016 by careysub]

Sulaiman - 6-7-2016 at 07:19

A potential solution may have been invented in 1815 https://en.wikipedia.org/wiki/Davy_lamp
with minor modifications ...

Some reliable simple flame arrester may help ? https://en.wikipedia.org/wiki/Flame_arrester

careysub - 6-7-2016 at 10:23

Quote: Originally posted by Sulaiman  
A potential solution may have been invented in 1815 https://en.wikipedia.org/wiki/Davy_lamp
with minor modifications ...

Some reliable simple flame arrester may help ? https://en.wikipedia.org/wiki/Flame_arrester


Interesting. I knew about the safety lamp, but had not considered this.

Actually the use of the carbon filter, upstream of the fan which is the preferred arrangement, might be an effective flame arrester. The air must pass thought the 2" carbon bed to get to the fan and motor. This should have the same effect in preventing propagation of a flame front back to the hood, especially since the flame front has to move against the air flow which would in the neighborhood of 10 ft/sec, but 25 ft/sec at the throat of the filter.

(This posted before I could complete it.)

Attached in a paper on the flame front velocity of diethyl ether/air, which indicates a maximum velocity of 70 cm/sec. This suggests that it cannot propagate against the duct flow regardless.

Of course a flame arrester (if it works) prevents propagation not ignition, and the flame would probably continue to burn downstream from the motor once the gas mixture was ignited. If this happened just before the external vent this result may not be too bad, if there is nothing combustible right outside the vent.

It would be interesting to set-up an outdoors duct/motor test set up to investigate ignition and propagation.

[Edited on 6-7-2016 by careysub]

Attachment: gillespie2012.pdf (713kB)
This file has been downloaded 523 times


Sulaiman - 6-7-2016 at 10:49

Please take with caution ... an idea, not from experience

Magpie - 6-7-2016 at 10:53

Quote: Originally posted by careysub  
I need 285 CFM for 1 FPS with the sash wide open on a 36"x48" window.


So, you have a 3'W x 4'H nominal window. Mine is a nominal 4'W x 5'H. A few times I have wished my working space was wider, and a few times higher.

So with your window full open you have an opening of of 3' x 1.6', approximately - correct? This will be a good working opening and I assume will give you 1.0 fps face velocity at 285 cfm? When you bring the sash down to half that opening (0.8') your face velocity will double to 2 fps. I predict that will blow out your bunsen burner.

Quote: Originally posted by careysub  

The total distance from the 8" x 12" trunk duct plenum on top of the fume hood (I intend to use a slot along the top for extraction) using 8" ducting is 4 feet to the garage side vent with one 90 degree bend. I calculate a pressure drop of 0.01" (rounding up). So 310 CFM at 0.375" looks good.


I'm really glad to see that you are staying with the 8" diameter duct. So many people go to 4-5" dryer duct, which in my thinking would be terrible due to the corrugation and small diameter.

So you have a run of 4' and 2 ea 90° elbows (counting the one at the hood plenum). Is that correct? As, you say, that won't be much duct pressure drop. I assume you included the contraction loss at the plenum and the louvre loss at the exit vent. I'll do a calculation of my own to provide a check.

Quote: Originally posted by careysub  

OTOH, I was also looking at this, and using a carbon filter (static pressure drop 0.5") to reduce odoriferous releases:
https://www.amazon.com/Can-Fan-Inline-6-Inch-Minute/dp/B004C...
which delivers 283 CFM with a filter.

At $100 it could be considered a replaceable item if it fails from corrosion.

Having a carbon filter upstream may provide some protection (I know they do not do much with acid gases), and I would endeavor not to put lots of corrosive gases through it (the hood is after all primarily a safety system, not a chemical disposal system). Proper experiment set-up should try to capture and neutralize such releases, and I do have the option of doing some simple operations outside if corrosive release seems unavoidable.


I'd forget about carbon filter, scrubbers, etc, if at all possible. They will eat all your lunch in pressure drop.

Quote: Originally posted by careysub  

Getting an indutrial type blower rated as "explosion proof" (is "spark resistant" a suitable substitute?) is a problem, it looks like it multiplies the cost by about 10, pushing it into the "unaffordable" column, and makes units delivering adequate static pressure in my size very hard to find at any price, and many of the units offered in this category are extremely loud.


This is why I advocate the belt driven squirrel cage blower. The motor is not in the air flow. A squirrel cage is a centrifugal blower and can inherently deliver more SP than any axial flow fan such as you are considering.

Noise is a consideration. Some knowledgeable posters here have stated that most of the noise is just due to air rushing through the duct.


careysub - 6-7-2016 at 12:09

Quote: Originally posted by Magpie  
Quote: Originally posted by careysub  

I need 285 CFM for 1 FPS with the sash wide open on a 36"x48" window.


So, you have a 3'W x 4'H nominal window. Mine is a nominal 4'W x 5'H. A few times I have wished my working space was wider, and a few times higher.

So with your window full open you have an opening of of 3' x 1.6', approximately - correct?


I estimated 33" wide. But in that ballpark, I need go look at an actual window.

Quote:

This will be a good working opening and I assume will give you 1.0 fps face velocity at 285 cfm? When you bring the sash down to half that opening (0.8') your face velocity will double to 2 fps. I predict that will blow out your bunsen burner.


When would I need to reduce the sash height by that much?

In college I worked with a fume hood that did not have a variable sash height. I've never worked with one that did, so the necessity of doing that is not obvious to me.

Quote:

So you have a run of 4' and 2 ea 90° elbows (counting the one at the hood plenum). Is that correct? As, you say, that won't be much duct pressure drop. I assume you included the contraction loss at the plenum and the louvre loss at the exit vent. I'll do a calculation of my own to provide a check.


The area of an 8" duct is about 50 square inches, the slot into the trunk duct would maybe be 100 square inches, also the exit vent is a louvered 13"x17" window that would be blocked by a steel sheet and use an 8" x 12" right angle register to exhaust. I assumed no significant pressure loss at either end since there was no constriction, just the right angle turn.

Quote:

I'd forget about carbon filter, scrubbers, etc, if at all possible. They will eat all your lunch in pressure drop.


They introduce a specific, known static pressure drop, 0.5" according to the manufacturer of the one I was looking at. It is the only significant pressure loss in the system. I can see no reason that this cannot simply be factored into the fan selection, as I am doing.

Quote: Originally posted by Magpie  

Quote: Originally posted by careysub  

Getting an industrial type blower rated as "explosion proof" (is "spark resistant" a suitable substitute?) is a problem, it looks like it multiplies the cost by about 10, pushing it into the "unaffordable" column, and makes units delivering adequate static pressure in my size very hard to find at any price, and many of the units offered in this category are extremely loud.


This is why I advocate the belt driven squirrel cage blower. The motor is not in the air flow. A squirrel cage is a centrifugal blower and can inherently deliver more SP than any axial flow fan such as you are considering.


Is there any particular reason why the bilge blower approach would not work? They are rated to be non igniting (they have a UL rating for this), and the pressure/flow rate chart seems to work out.

I did look around for some belt driven squirrel cage blowers, but found none that were small enough. No doubt they exist somewhere, but have proven hard to locate. Yours in larger than what I can use, I haven't found one even as small as that. This general design seems to be reserved for systems with CFMs and price tags both north of 1000.

Magpie - 6-7-2016 at 13:49

Quote:
Quote:
Quote: Originally posted by careysub  

When would I need to reduce the sash height by that much?


I pull my window down when I think there is a potential for an explosion or an implosion. There's always a potential for an implosion when doing a vacuum distillation.

Quote: Originally posted by careysub  

Is there any particular reason why the bilge blower approach would not work? They are rated to be non igniting (they have a UL rating for this), and the pressure/flow rate chart seems to work out.


I have nothing against bilge blowers if they have adequate flowrate. I would not want to use them in parallel due to the likelyhood of push-pull oscillation of airflow. Also there is the issue of running on 12vdc. I would not want to have to monkey with that.

In regard to noise my blower is rated at 46db at 5 ft.

In regard to corrosion I think this may be less of a concern than we think. Most of the airflow is just that, air. I have given my system extended service with Cl2 and HCl and other likewise corrosive gases. The vent louvre shows no signs of corrosion. It is most likely made of aluminum or steel and is painted with acrylic house paint. I have not inspected the fan blades or fan housing internal surfaces however. My fan has been in service for 11 yrs and continues to work well. I haven't even had to tighten or otherwise adjust the belt. Zero maintenance.

addendum 1:

Here's a possibility for you at $251 for the blower only. You would have to add your own motor, direct drive or with a belt. My motor is 1/4 hp and runs at 1725 rpm. The blower runs at 1000 rpm. My guess is that this would be a good match for this blower to give you the SP and airflow that you need. blower

I'll continue to look for a blower.

[Edited on 6-7-2016 by Magpie]

[Edited on 7-7-2016 by Magpie]

Magpie - 7-7-2016 at 19:26

I did the head loss calculation. Assuming a flow of 285 cfm, 6 ft of smooth 8"pipe, 2-90° ells, 1 protruding pipe exit, and 1 protruding pipe entrance, I came up with 0.12" H2O pressure drop. So I have to concur with you that a blower capable of 3/8" H2O SP seems adequate.

I crawled up in the rafters and inspected my blower today. Everything looks solid although the pipe hanger right before the blower was slightly loose. There are signs of corrosion around some of the edges of the SS plenum and around the blower shaft bearing.

Here's some pictures:

blower inlet.jpg - 96kB
blower inlet


blower drive end.jpg - 120kB
blower drive end & bearing


blower motor & belt.jpg - 110kB
blower motor & belt


Magpie - 8-7-2016 at 13:58

In the vein of Mark Twain, my earlier reports of "no findings" for my 11 yr old blower were greatly exaggerated. Further inspection has revealed heavy deposition on the inside of the blades as shown below:

rubber boot pulled back.jpg - 127kB
rubber boot pulled back


blower forward-curved blades.jpg - 148kB
forward-curved blower blades

I will likely remove the blower wheel so I can clean it properly.

As can be seen the end of the steel shaft is heavily rusted but the epoxy coated housing, also steel, is not. The blades look to be somewhat rusted, however. I'll be able to tell more after I clean them.

The inside of the 8" duct has only a light coating of dust.

This inspection was prompted by a performance drop I detected today as determined by a tissue streamer compared to what I recall when the blower was first installed.



[Edited on 8-7-2016 by Magpie]

[Edited on 9-7-2016 by Magpie]

[Edited on 9-7-2016 by Magpie]

careysub - 9-7-2016 at 05:47

Very interesting Magpie, thanks!

But first I have to clean out the area of the garage where the fume hood would go. That is a bit of a project in itself!

Plans of course will continue to be refined until it comes time to actually build, e.g., I am now considering the American Craftsman 37.75 in. x 56.75 in. 70 Series Double Hung window at Home Depot for a minor price increase (whole project cost considered), slightly larger, and gives me maximum flexibility with flow and shielding.

Looking at the Dayton blower you linked to, that is actually a direct drive - not a belt drive model. It appears that all of the belt drive units are larger than what I need. But
I am considering the direct drive version, perhaps with the totally enclosed motor, as I don't really want to mess with the belt anyway. This also has the motor out of the air flow, and perhaps a metal screen - a la the Davy safety lamp - could be installed between the motor and the blower.

[Edited on 9-7-2016 by careysub]

Texium (zts16) - 9-7-2016 at 06:14

I went ahead and split this discussion of fume hoods into its own thread and stickied it.

Magpie - 9-7-2016 at 09:09

Quote: Originally posted by careysub  


This also has the motor out of the air flow, and perhaps a metal screen - a la the Davy safety lamp - could be installed between the motor and the blower.


I believe that a direct drive motor would be safe as it is out of the exhaust path. Also the area around the shaft is sealed by 2 ball bearings. And due to its location at the center of a centrifuge is at a vacuum condition. A Davy flame arrestor certainly wouldn't hurt anything, however. I've seen these on some carburetors.

My motor is a split-phase, sleeve bearing, 1/4HP (Grainger 5K907). All this time I thought it had sealed ball bearings! I will definitely oil the bearings before putting it back in service.

Right now I'm in the middle of my millwrighting. The wheel is ready to pull off the shaft. But it's not going to come off without a fight. I'm soaking the hub/shaft interface with penetrating oil.

careysub - 9-7-2016 at 16:38

BTW - I've dropped the idea of the carbon filter. Nearly all of the time it would be a waste.

If I contemplate a procedure that is especially odoriferous, I would probably set up a special apparatus to deal with the fumes.

Texium (zts16) - 9-7-2016 at 17:08

I have a squirrel cage fan from my old AC unit, and it's a direct drive, so the motor is inside of the cage. Would this be inappropriate to use as an exhaust fan, even if I were to give the whole thing a good coat of epoxy? I was thinking that if I have to, I could remove the motor and set it up as a belt driven fan like Magpie's, but I'd of course prefer to keep it the way it is if possible.

I've read that the motors in these things have to be sparkless because of the possibility of igniting dust in AC ducts, so I'm not concerned about it starting fires, I just want to know if the motor will hold up in that environment.

Magpie - 9-7-2016 at 17:44

I think the motor wouldn't last long in the corrosive exhaust stream.

I wouldn't trust that sparkless claim, not with a duct full of ether fumes above the LEL. :o

I took a look at my old furnace blower and decided its performance characteristics were not matched to the needs of my hood. It provided high flow at low SP where my hood needs medium flow at high SP.

[Edited on 10-7-2016 by Magpie]

Texium (zts16) - 9-7-2016 at 17:48

Quote: Originally posted by Magpie  
I think the motor wouldn't last long in the corrosive exhaust stream.

I wouldn't trust that sparkless claim, not with a duct full of ether fumes above the LEL. :o
Ok, thanks. I'll see how feasible it would be to change the configuration of that motor then.

Magpie - 10-7-2016 at 12:24

Quote: Originally posted by careysub  
Very interesting Magpie, thanks!

You are welcome.

Quote: Originally posted by careysub  

But first I have to clean out the area of the garage where the fume hood would go. That is a bit of a project in itself!
Amen.


Quote: Originally posted by careysub  

Plans of course will continue to be refined until it comes time to actually build, e.g., I am now considering the American Craftsman 37.75 in. x 56.75 in. 70 Series Double Hung window at Home Depot for a minor price increase (whole project cost considered), slightly larger, and gives me maximum flexibility with flow and shielding.
Good idea. I'm sure you will appreciate the extra space.

Quote: Originally posted by careysub  

Looking at the Dayton blower you linked to, that is actually a direct drive - not a belt drive model. It appears that all of the belt drive units are larger than what I need. But
I am considering the direct drive version, perhaps with the totally enclosed motor, as I don't really want to mess with the belt anyway. This also has the motor out of the air flow, and perhaps a metal screen - a la the Davy safety lamp - could be installed between the motor and the blower.


Totally enclosed fan cooled (TEFC) motors are the favorite of industry where there can be wet environments. Such as an outside area with no roof. Also picture an operator with a high pressure hose cleaning up a big spill of pulp slurry. These are not spark proof and IMO are a waste of money for our application. Instead I recommend a "drip-proof" motor - which is what I have.

While on the subject of motors I feel the "split-phase" is adequate, which is what I have. We don't have high starting torque or high cycling on and off which might require the more expensive motors like "capacitor start," etc. We also don't run continuous duty which could justify a more expensive motor that draws fewer amps.

Also the sleeve bearings that came with my motor seem to be adequate vs spending more money for ball bearings.

I'm certainly not an expert on the subject of motor selection, these are just my studied opinions. If anyone wants to add to this discussion I welcome that. ;)

Texium (zts16) - 10-7-2016 at 12:44

Well you probably know more about them than most people on here, so your studied opinions are greatly appreciated!

Magpie - 11-7-2016 at 08:44

I'm still in the middle of fume hood maintenance. Here is a picture of the outlet louvre. It is discolored after 6 years of use (house was painted 6 years ago).

outlet louvre.jpg - 113kB

This morning I cleaned it with dish soap and hot water using a long-handled scrub brush. It looks like new now, almost. I will give it a coat of paint in a few days.

I'm anticipating that the blower wheel will be pulled today after I buy a hub puller.


Loptr - 11-7-2016 at 12:42

Nice find with the 80/20 erector set!!!

This will be taking my fume hood construction in a new direction.

How expensive do you expect this to turn out with 80/20 pieces?

Magpie - 11-7-2016 at 13:18

There is a pressure loss we have been forgetting, ie, that of the hood itself. Kewaunee shows that for a 100 fpm face velocity, 4' hood with 8.1ft^2 open area this pressure drop is 0.25" H2O. Be sure to take this into account.

http://kewaunee.com/uploadedFiles/Main/Home/Laboratory/Manua...

Note that Kewaunee does not recommend a face velocity less than 100 fpm (1.67 fps)!

I am preparing a tutorial/instructable for calculating pressure drop for fume hood systems. I should have it ready in a day or two.

[Edited on 11-7-2016 by Magpie]

careysub - 12-7-2016 at 06:48

Quote: Originally posted by Loptr  
Nice find with the 80/20 erector set!!!

This will be taking my fume hood construction in a new direction.

How expensive do you expect this to turn out with 80/20 pieces?


As a basic design, a hood made with four 7' tall pieces, four 30" deep side pieces, four 36" wide front/back pieces, the necessary connectors, and four economy leveling feet comes to $276.

I intend to add a few more pieces though - two side pieces and a free side-to-side piece that can be attached to these two side pieces as a way of supporting frames and equipment. With proper planning using the perforated version of the square tube (pre-positioning threading inserts in the frame, etc.) you can easily think vertically - attaching things to the frame suspended above the work table surface (at extra cost).

Other options that can increase price - the use of their flush mounting pins on the sides where sheet metal attaches. This is not essential though since you can simply drill holes in the sheet where bolt heads are. I intend to attach to galvanized steel sheet by simply drilling into the aluminum frame and using flange head screws with washers.

[Edited on 12-7-2016 by careysub]

MrHomeScientist - 12-7-2016 at 07:09

Quote: Originally posted by Magpie  
I am preparing a tutorial/instructable for calculating pressure drop for fume hood systems. I should have it ready in a day or two.

That would be extremely valuable Magpie! I'm looking in to making a hood in the near future so this will be a great help. Definitely let us know when that's up. Worth a separate topic here IMO.

Magpie - 12-7-2016 at 09:20

Quote: Originally posted by MrHomeScientist  

That would be extremely valuable Magpie! I'm looking in to making a hood in the near future so this will be a great help. Definitely let us know when that's up. Worth a separate topic here IMO.


Thanks. I'm planning on placing it in Prepublication. But I will place a link in this thread.

blower maintenance continuation

Magpie - 12-7-2016 at 12:46

The blower wheel was removed this morning using a hub puller, a 12", and a 15" crescent wrench, and the help of my strong son.

The following pictures show the results after 11 years of hobby use:


9 inch blower wheel cleaned with water.jpg - 215kB
9 inch blower wheel washed with water


blower wheel outer edge.jpg - 205kB
blower wheel outer edge


blower shaft and inner bearing.jpg - 113kB
blower shaft and inner bearing


My plan is to remove the rust on the blades and repaint with epoxy paint.



[Edited on 12-7-2016 by Magpie]

Magpie - 13-7-2016 at 13:37

FYI I have posted a procedure for calculating the pressure drop in a fume hood system in Prepublication here


Loptr - 14-7-2016 at 10:47

Quote: Originally posted by careysub  
Quote: Originally posted by Loptr  
Nice find with the 80/20 erector set!!!

This will be taking my fume hood construction in a new direction.

How expensive do you expect this to turn out with 80/20 pieces?


As a basic design, a hood made with four 7' tall pieces, four 30" deep side pieces, four 36" wide front/back pieces, the necessary connectors, and four economy leveling feet comes to $276.

I intend to add a few more pieces though - two side pieces and a free side-to-side piece that can be attached to these two side pieces as a way of supporting frames and equipment. With proper planning using the perforated version of the square tube (pre-positioning threading inserts in the frame, etc.) you can easily think vertically - attaching things to the frame suspended above the work table surface (at extra cost).

Other options that can increase price - the use of their flush mounting pins on the sides where sheet metal attaches. This is not essential though since you can simply drill holes in the sheet where bolt heads are. I intend to attach to galvanized steel sheet by simply drilling into the aluminum frame and using flange head screws with washers.

[Edited on 12-7-2016 by careysub]


I went ahead and ordered the books they offer for free. They shipped out yesterday, so I should have them soon and have some idea of how all this fits together.

The books were free, so I figured why not.

careysub - 14-7-2016 at 11:23

Quote: Originally posted by Loptr  


I went ahead and ordered the books they offer for free. They shipped out yesterday, so I should have them soon and have some idea of how all this fits together.

The books were free, so I figured why not.


Books? I saw a bunch of PDF downloads, but what books?

Magpie - 20-7-2016 at 16:20

My fume hood maintenance is still in progress and will be for another week or two.

The blower wheel was sand blasted to remove rust and then spray painted.

painted blower wheel.jpg - 179kB
painted blower wheel

Today I removed the upper baffle and hosed it down in the backyard. Visibly there was only a layer of dust above the angled part.

upper baffle removed.jpg - 120kB
upper baffle

The ss floor pan was removed for cleaning underneath where there was a surprising amount of loose dirt.

ss hood floor pan.jpg - 110kB
ss floor pan

With the pan in place I flushed the plastic duct from both ends with a garden hose/nozzle, catching the wash water in the pan.

Here's a couple pictures of the hood with the upper baffle and pan removed. You can see the slight yellowing of the epoxy painted walls. I believe this is due to exposure from my 400w UV light when making CCl4.

hood outlet (8 inch).jpg - 95kB
8" hood outlet

hood with upper baffle removed.jpg - 100kB
hood w/upper baffle removed


CaptainPike - 23-7-2016 at 10:08

WOW – you guys are like – have your SHITE TOGETHER!!

I thought my idea of putting an old box fan in the upper part of the window at my table was my being really responsible and innovative.

Has anyone had any luck constructing an articulating duct with a funnel end which can be lowered and placed above and near the source of fumes? (like some college labs have)

There've only been a few times when I had to exit the building under duress because the ether fumes or the HCl gases were choking me.


Magpie - 28-7-2016 at 08:43

This morning as I went out to weed my garden I noticed a band of dead grass about 4 feet long. I then remembered that it is in the spot where I washed off the angled part of my hood upper baffle. Hopefully it will grow back green.



grass affected zone.jpg - 332kB

careysub - 28-7-2016 at 12:31

I hope you resisted the temptation to lick it!

(Probably just killed the foliage. I doubt it poisoned the earth.)

[Edited on 28-7-2016 by careysub]

Magpie - 1-8-2016 at 10:40

It was a little cooler today so this morning I reinstalled my blower wheel. All that is left now is to connect the duct to the blower. By noon it was too hot in the attic so I quit for the day.

Below is a picture of the outlet plenum, something I really hadn't shown before:



outlet plenum.jpg - 114kB

Loptr - 1-8-2016 at 10:53

Quote: Originally posted by careysub  
Quote: Originally posted by Loptr  


I went ahead and ordered the books they offer for free. They shipped out yesterday, so I should have them soon and have some idea of how all this fits together.

The books were free, so I figured why not.


Books? I saw a bunch of PDF downloads, but what books?


I believe that I requested the books through this page.

https://8020.net/requests

I didn't see the books were available as PDF at the time, but they sent me print outs of everything without costing me a penny. Besides, I prefer books to PDFs, anyway.

[Edited on 1-8-2016 by Loptr]

Magpie - 3-8-2016 at 09:42

My hood maintenance was completed this morning. The first picture below shows airflow with the upper baffle still removed. The second picture is at the hood face with the baffle reinstalled. The paper is a strip of facial tissue paper (Kleenex).

Performance shows some improvement, IMO.

dangleometer at hood outlet.jpg - 100kB dangleometer at hood face.jpg - 127kB

BTW, here's a very useful site that I stumbled upon:

http://www.centralblower.com/index.html

[Edited on 3-8-2016 by Magpie]


[Edited on 3-8-2016 by Magpie]

JJay - 28-12-2016 at 02:29

I've been giving some thought to building a benchtop fume hood. I was thinking about constructing it out of drywall and sealing it together with plaster of Paris, making the floor a flat basin. That way, it could withstand some pretty large spills of nasty materials like concentrated sulfuric acid and could resist flames. Drywall is pretty brittle, though, and it's really not that lightweight... I wonder how hard it would be to work fiberglass into the construction....

There is a lot of appeal to using a small diameter exhaust, but with a 4 inch fan and a 4 foot wide fume hood, I'd only have 4.5 inches of working height at 60 fpm face velocity (assuming a 100 CFM fan). I haven't used a fume hood since high school and have never used one with complex apparatus... how much working height is really necessary?

[Edited on 28-12-2016 by JJay]

aga - 28-12-2016 at 09:37

A decent fan/blower is certainly a hard-to-come-by item (here at least).

Mine ended up being a standard bathroom ventilator, which is pretty crap, but works.

It chugs away and removes nasties from the hood <i>just fast enough</i> when the sashes are closed.
Sash open = face full of honk.

So far it's handled NOx and Cl2 and is still chooching.

In the end, the capabilities of the extraction system have to be known, and the hood used within those known limitations.

i.e. there will definitely not be any bromine made in my 'hood until the fan system is upgraded.

[Edited on 28-12-2016 by aga]

Corrosive Joeseph - 28-12-2016 at 10:39

Seeing as this is the sticky thread, I'll drop these here......................



Attachment: Chemical Fume Hood Guide 1.pdf (78kB)
This file has been downloaded 531 times

Attachment: Chemical Fume Hood Guide.pdf (772kB)
This file has been downloaded 2710 times

Attachment: Chemical Fume Hood Handbook.pdf (201kB)
This file has been downloaded 472 times

Attachment: Fume Hoods - Design, Construction, Maintenance and Use.pdf (298kB)
This file has been downloaded 510 times

Attachment: Fume Hoods - Ventilation.pdf (98kB)
This file has been downloaded 519 times

Attachment: How to Select the Right Laboratory Hood System.pdf (322kB)
This file has been downloaded 412 times

Happy f%@king commercialized religious holiday................ :D


/CJ

[Edited on 28-12-2016 by Corrosive Joeseph]

charley1957 - 16-7-2017 at 09:26

Quote: Originally posted by Magpie  
Whatever fan you select it must be able to deliver enough flow to provide 1.0-1.5 fps face velocity at your hood opening. It also must be corrosion resistant and spark free in the exhausted air environment.

If you don't have a constant flow design your face velocity is going to vary all over the place, depending on sash position.

My squirrel cage fan blades are epoxy coated steel. I have never inspected my fan internals since installation (11 yrs ago). I just know that the fan still works well.

3/8" SP looks a little weak to me but I don't know the diameter, shape, and length of your ducting. My fan delivers 400-500 cfm at 3/4" SP.

All of this guidance I have repeated several times in the hood threads to various posters. In the end I find that people just do whatever they had in mind in the first place. Everybody has their own space and money constraints. As garage chemist said: "any ventilation is better than none." :D

[Edited on 6-7-2016 by Magpie]


That last line, any ventilation is better than none, is a good one. Years ago I was part of a forum of Robert Bruce Thompson's before he changed it all and it became a home schooling forum. There was a member there who called herself Xylene, and she often posted pics of her workups. Her fume hood was a piece of round rigid tin duct, about 3" diameter, with a computer fan taped to the end of it closest to the reaction, and the other end was poked out of the nearby open window. Seemed to work just fine for her.

Texium (zts16) - 16-7-2017 at 10:59

I'm continuing to look at fans for the fume hood that I want to build and today I found this one on Amazon. I think it looks pretty promising. $90 including shipping, 265 cfm, and the motor is out of the airflow. It looks like it should be easy to hook up too since the intake and outlet are already flanged and should be easy to connect to any sort of duct that I would use.

Any input on it from the resident fume hood experts? Just want to make sure it's good before I buy it.

JJay - 20-7-2017 at 13:11

I don't know much about that fan.... I've been putting a 2'x4'x4' enclosure together for my hood and am super tempted to use a box fan for ventilation. I am going to use vinyl for the sash (at least initially) since it is cheap, easy to work with, fairly chemically resistant, and hard to ignite. But in a perfect world I'd build it out of fiber-reinforced concrete panels with a squirrel cage fan and a glass/polycarbonate laminate sash.

[Edited on 20-7-2017 by JJay]

Geocachmaster - 20-7-2017 at 17:07

I just ordered the 460 CFM version of that fan, zts. It's supposed to arrive on Saturday and I should get my fume hood built this weekend. The plan is 4 feet long, 42 inches high on the inside. My dad is actually a carpenter so it should be built pretty well. ;)

When it gets done I'll post pictures here and tell you how the fan is.

JJay - 21-7-2017 at 17:04

I've been doing some reading in NFPA 45. It gives specific requirements for laboratory fume hoods in fire codes that have been adopted pretty widely in the U.S.. This is the 2004 edition, so some updates have probably been made since then, but it contains a few requirements that I found surprising:

1. A fume hood is supposed to be able to contain a 2L spill.
2. A fume hood is supposed to have a flow sensing device permanently installed.
3. Many box fans cannot be used for ventilating a fume hood. There is a requirement that the motor and controls be out of the usual flow of air unless approved for use in a fume hood. This surprised me mainly because I've used box fans that were permanently installed in a professional environment for ventilating corrosive and toxic gases before, but those box fans were clearly designed and manufactured for that purpose.
4. An automatic fire protection system is required for handling flammable liquids in your fume hood unless it is constructed of materials with a Class I flame spread rating: http://sfm.dps.louisiana.gov/doc_flamespread.html So it looks like drywall and fire retardant plywood are ok, but most plywood is not sufficient.
5. Flammable duct materials are not to be used except with "special local exhaust systems." I am planning on using aluminum, but it is interesting that there is an exception for flammable duct materials.
6. The [optional] sash shall be "glazed" with materials designed to protect the fume hood's operator.

I'm planning on coating the inside of mine with gypsum, and my fan has a disc covering the motor and keeping it out of the flow of air, so I think it be permitted to handle flammable liquids and just barely avoid the requirement of an automatic suppression system, although I will consider another fan....

I'm not really sure what to think about the requirement that the sash be glazed. No specific glazing requirements are given, but a reference is made to Annex C, an optional part of the standard on explosion protection. I think I will be ok with a rollup vinyl sash?

The part I'm not sure about is the permanent flow sensing device. Does anyone know what form that should take? Also, does anyone have a more up-to-date version of NFPA 45?

Attachment: NFPA 45 2004 (1).pdf (3.2MB)
This file has been downloaded 241 times

[Edited on 22-7-2017 by JJay]

Geocachmaster - 22-7-2017 at 15:57


We got the main part of the hood built today and installed the blower in the window. Tomorrow we will install lights, sash, water and power, and we will hook up the duct work.


As for the fan on amazon zts, I would say it's okay for fume hood. Not ideal though. The motor is partway in the path of the air. It also has air intake of the opposite side of the flange. I will have to cover over this with tape. There are holes in the motor casing to allow air to pass through and cool the motor. I'm not too worried about this though because the air current should keep corrosives out of the internals. This is for the 465 CFM version so the 260 one might be different.


IMAG0016.JPG - 1.5MB

JJay - 22-7-2017 at 16:51

That looks quite sturdily constructed. Is that a baffle in the back?

I attached some vinyl to the front of mine with Velcro. I'm not 100% ready to recommend vinyl sashes for general use, but so far so good....

IMG_20170722_163741.jpg - 72kB

JJay - 22-7-2017 at 17:10

Oh and while researching glass glazing, I learned that "glazing" is simply the process of mounting a see-through panel. So a glazed sash is one that contains a pane, and an unglazed sash would have an empty space. I guess probably everyone else knew that already, but it was new to me....

Geocachmaster - 22-7-2017 at 17:27

It is sturdy indeed. When it's finished I estimate the total cost to be $200, including the fan. If my dad charged me for labor then the cost would be more like $800, but luckily he's working for free this weekend ;). There is in fact a baffle in the back. 7 inch gap at the bottom, 1 1/2 inch gap at the top. I don't know what the best configuration is but I figured that most of the air should be drawn over the work surface and some air out the top to get rid of less dense gasses. This baffle configuration just looked right to me.

JJay - 22-7-2017 at 17:38

I think the baffle was an excellent idea.

Magpie - 23-7-2017 at 09:52

nice work, both of you


macckone - 23-7-2017 at 10:39

Useful book if you don't want to buy a fan:
http://gingerybookstore.com/product36.html

This is relatively expensive for what it provides but could
be useful for someone that can't find exactly the right fan.

There are various baffles that can be used to keep a bunsen
burner from getting blown out by the air flow.
The simplest one is simply a U shaped piece of
sheet metal that is oriented away from the face.

macckone - 23-7-2017 at 10:44

Also someone asked about air flow indicators.
The simplest air flow indicator is simply a ribbon
located near the sash opening. I have seen
these in labs to meet the NFPA requirement.
The other option is a pitot tube. The book I
mentioned contains instructions for constructing one.

JJay - 24-7-2017 at 09:29

I checked my local laws, and there's no specific NFPA requirement that I have to meet, but there is an IFC 2015 requirement:

5003.8.5 Exhausted enclosures. Where an exhausted
enclosure is used to increase maximum allowable quantity
per control area or where the location of hazardous materials
in exhausted enclosures is provided to comply with
the provisions of Chapter 60, the exhausted enclosure shall
be in accordance with Sections 5003.8.5.1 through
5003.8.5.3.
5003.8.5.1 Construction. Exhausted enclosures shall
be of noncombustible construction.
5003.8.5.2 Ventilation. Exhausted enclosures shall be
provided with an exhaust ventilation system. The ventilation
system for exhausted enclosures shall be
designed to operate at a negative pressure in relation to
the surrounding area. Ventilation systems used for
highly toxic and toxic gases shall also comply with
Items 1, 2 and 3 of Section 6004.1.2. The ventilation
system shall be installed in accordance with the International
Mechanical Code.
5003.8.5.3 Fire-extinguishing system. Exhausted
enclosures where flammable materials are used shall be
protected by an approved automatic fire-extinguishing
system in accordance with Chapter 9.

Chapter 9 mainly discusses sprinklers but also has reference to "alternative" automatic fire suppression systems and prescribes specific NFPA sections.

Geocachmaster - 26-7-2017 at 17:51

I finished the fume hood on Monday night. I can't take good pictures, but I can take good video!

https://youtu.be/wijigT7xVIk

I'm very happy with it and it got its first use tonight. I did some smoke tests and everything looks good so far but I'm going to do something with chlorine next week which will really test the fume hood.

JJay - 27-7-2017 at 09:31

Very cool. Mine needs some sort of baffle to ensure that both lighter than air and heavier than air gases are eliminated.

Reboot - 12-11-2017 at 10:33

I've started work on what I hope will be a small ductless hood eventually. I started with a nice heavy-duty professional kitchen table with a 12 gauge 304 stainless top. Stainless comes in a lot of grades; for a lab counter (or kitchen counter) you want either 304 or 316 (surgical stainless.) Most other grades (like 430) aren't suitable; they corrode too easily from chemical exposure. 304 and 316 stainless is non-magnetic; you can't stick a magnet to it. Cheaper grades are magnetic, so that's the easy test if you're wondering what something is.

hoodtable.jpg - 89kB

I'll be installing a number of panel-mount switches and gauges, which can give a very professional custom look with surprisingly little effort.

To start, carefully decide where you want the control to be and mark the center of the location.

hoodbuttonmark.jpg - 73kB

Next, take a narrow ('centering') punch and put it on the mark. Give it a good whack or two with a hammer, just enough to put a small indentation in the metal. This keeps the drill bit from wandering off in the next step.

hoodtablepunch.jpg - 62kB

Chuck a hole saw into a decent drill (corded or more powerful cordless ones will work well.) The switch I want to install fits a 19 mm (3/4") hole, so I'm using a 3/4" hole saw. The drill bit in the center of it guides the hole saw itself; start drilling with this bit in the indentation you made with the punch. This is an easy process; just take your time and keep it strait.

hoodtabledrilling.jpg - 64kB

Once the hole is cut, the panel mount switch slides in from the front and a nut gets tightened onto it from the back to hold it in place. (This switch is waterproof and has an o-ring on it to seal it to the panel. It can also light up when on, if you wire it that way.)

hoodtablebutton1.jpg - 52kB

The wiring is a subject for another day. The system will use 12 volt DC for the switches (for both safety and due to power limits on these switches.) The switches in turn will run relays that turn 120 volt AC power on and off to a number of items (hood fan, vacuum pump, coolant pump.)

The (already installed) red knob is an emergency kill switch; whack it and it will kill power to the whole apparatus. You can find these for about $10. If you want something more glamorous/capable, Eaton makes a super-sexy $200 version. :-)

hoodtablebuttondone.jpg - 49kB

The plan is to eventually also install a vacuum regulator and some panel-mount vacuum/pressure gauges into the top of the table to one side. The process for a gauge is similar, you just need a much bigger hole saw. I'd like to have at least one hood suction gauge (to verify good airflow) and a big old 4" analog vacuum gauge at the least. The fan and filter system will be under the table (with some sort of enclosure for appearances) There are still a lot of interesting design decisions to make before this comes together, but I'm having fun!

aga - 10-1-2018 at 10:50

Today i found a small-ish industrial extractor at the scrap yard - 3.50 euros.

It verks !

Now to build a box so it can replace my feeble 'hood extractor.

Maybe then i'll have the guts to use that fume hood again in anger.

It's not been used much since i ended up inhaling a few lung-fulls of dioxane.

zed - 8-6-2018 at 11:25

Whenever possible, I've worked my chemistry in a hood.

That being said, the high-tech, state of the art, hood that I mostly worked under, in college... Failed very reliably, whenever someone happened to open one of the doors from the outside courtyard, into the lab. Especially so, on breezy or windy days.

Kind of like a fireplace, it would abruptly lose its "draw". In fact, despite perfect design, and a powerful fan, my fancy hood, would generally blow "backwards".

The only remedy was to keep sharp ears, schedule experiments for quiet times, and when the outer doors were unexpectedly opened, to quickly lower the glass and close the hood.


Texium (zts16) - 8-6-2018 at 12:16

My fume hood blows out the rear wall of my garage, so I simply open the garage door about 6 inches to allow airflow to enter the room from the opposite side.

Corrosive Joeseph - 8-6-2018 at 14:39

Quote: Originally posted by macckone  
Useful book if you don't want to buy a fan



'How to Design Centrifugal Fans for the Home Shop' - David J. Gingery

"Build Inexpensive Powerful Blowers For Many Uses. . .

Build a dust precipitating cyclone, design sheet metal transition pieces, balance a dust collection system, build a static balancing stand and more.
Learn how to build a simple manometer and pitot tube and actually measure and fine tune your custom air system.
This book will show you how to take pillow blocks, shafting, plywood, sheet metal and other common materials and build a dirt cheap blower that outperforms any make-do blower you might fine on the surplus market.
Let Dave show you how easy it can be to design a fan that will provide the volume and pressure you need for the system you're building."


http://libgen.io/book/index.php?md5=68E57ED8AEBDACEA7B372C4C...



/CJ

MJ101 - 17-6-2018 at 13:42

#macckone: Yes. A pitot tube is what you'd use, but there are also electronic devices.

https://www.epluse.com/en/products/air-velocity-instrumentat...

And of course, DIY. :)

https://forums.ni.com/t5/LabVIEW-Interface-for-Arduino/Measu...

Of course you'll have to vett the sensor housing to make sure it will survive in the widest range of reaction.

Abromination - 16-7-2018 at 16:51

Well I built my own for under 30 bucks from a plastic bin, a PC fan and some vinyl laundry duct. Not ideal for really dangerous fumes although its great for everything else. If you have a budget and really need a good one, by all means follow magpie but this works well for small projects. I uploaded it to instructables and will attach the link.

https://www.instructables.com/id/Fume-Hood-for-Under-30/

CouchHatter - 30-12-2018 at 17:40

Does anyone have any experience with or knowledge of air foils? I've searched the forum and there's very little talk of them apart from airplane ones.
They can reduce air rolls and turbulence in the hood, it seems like a good feature. Anyone have one on their hood?

The best documentation I've found is this file someone posted previously here. Not sure what book it's from, but I'd love to read the whole thing.

My hood design is a bit atypical and would struggle to integrate the air foil as is shown in the book. Maybe I need to redesign it.

Corrosive Joeseph - 30-12-2018 at 19:04

Quote: Originally posted by CouchHatter  
Not sure what book it's from, but I'd love to read the whole thing.


Laboratory Fume Hoods: A User's Manual
By G. Thomas Saunders

/CJ

[EDIT] - https://www.wiley.com/en-us/Laboratory+Fume+Hoods%3A+A+User%...

[Edited on 31-12-2018 by Corrosive Joeseph]

CouchHatter - 31-12-2018 at 14:44

You are like Beetlejuice, CJ. Thank you very much! I've got a copy on the way.

I'll be posting some photos soon too!

raffike - 24-6-2019 at 06:56

My simple hood. 150mm tube and almost 200 watt ventilator(not seen in picture. Stainless steel seems to handle everything just fine and pipe is plastic. Have been in use for years and you can see,steel is like it just came from shop.

IMG_0095.JPG - 2.8MB

CouchHatter - 27-6-2019 at 17:45

Here is my completed fume hood. I finally installed the stack on the roof and it is functional! I am done painting for a while, something like 10-15 sessions to get all the parts covered. Ugh.

Sometime I'll make a thread to showcase all the bells and whistles and its construction.

DSC_0179.JPG - 523kB

Ubya - 28-6-2019 at 03:18

@CouchHatter pretty cool, and big! but what about that horizontal sash? never seen a fumehood using this type of design, is it effective?

Abromination - 6-7-2019 at 14:44

Nice hood, but strange sash design.

Anyways, I am working on my own hood right now and would like to know what y’all would suggest I do for baffle dimensions. My hood is 30 inches wide, 28 tall and 18 inches from the front of the actual opening to the very back. Sorry for using inches, I would have preferred not too.
I am using a 500cfm fan.

I’m not sure how much it matters with such a strong fan but it would be nice to have them anyways.



88A81255-07DF-4FEF-A934-3BBB081105FF.jpeg - 2.8MB

CouchHatter - 7-7-2019 at 17:39

It's 5' x 5' x 2'. No one ever said "I wish I made it smaller!":D I haven't seen a horizontal sash in use either, but it was addressed in Laboratory Fume Hoods: A User's Manual. I already owned the tempered window panes and simply cut another frame I had to size. So even if it goes in the bin I'm not out much... I can work around the large panes without sticking my head in, but qualitative testing will determine if it gets replaced with a more conventional solution, or not.

That was only one of the resources I used to design my hood. It was written in 1993 and I didn't really cross-check the horizontal sash thing with other books, so I will surely test it before using it much. Water is pulled 3/8" through a 3/16" ID tubing though, and the face velocity seems to be excellent. It completely removed the smoke from a tiny smoke bomb ~8 inches outside the hood. Now that firework season is over, I have a supply of bigger smoke bombs to really put it to the test. Just need some extra time.

Abromination, how wide is your duct? Look at page 21-22. The only dimension I would change would be the middle Slot B, to make it more close to the bottom third of the hood.

back baffle design p16-23

sash varieties p22-27


I made the pages barely too big so I'm just linking them in lieu of the 8MB attachment limit here.

Abromination - 8-7-2019 at 12:57

Quote: Originally posted by CouchHatter  
It's 5' x 5' x 2'. No one ever said "I wish I made it smaller!":D I haven't seen a horizontal sash in use either, but it was addressed in Laboratory Fume Hoods: A User's Manual. I already owned the tempered window panes and simply cut another frame I had to size. So even if it goes in the bin I'm not out much... I can work around the large panes without sticking my head in, but qualitative testing will determine if it gets replaced with a more conventional solution, or not.

That was only one of the resources I used to design my hood. It was written in 1993 and I didn't really cross-check the horizontal sash thing with other books, so I will surely test it before using it much. Water is pulled 3/8" through a 3/16" ID tubing though, and the face velocity seems to be excellent. It completely removed the smoke from a tiny smoke bomb ~8 inches outside the hood. Now that firework season is over, I have a supply of bigger smoke bombs to really put it to the test. Just need some extra time.

Abromination, how wide is your duct? Look at page 21-22. The only dimension I would change would be the middle Slot B, to make it more close to the bottom third of the hood.

back baffle design p16-23

sash varieties p22-27


I made the pages barely too big so I'm just linking them in lieu of the 8MB attachment limit here.


Here are the two real blower options I am looking at:
https://www.amazon.com/Fasco-A455-Centrifugal-Blower-Bearing...

https://www.amazon.com/gp/aw/d/B01MTFZSP5/ref=cm_cr_arp_mb_b...

I probably wont get the seaflow one, and the first fasco one doesn’t give me the input or output diameters.


The information on the baffles was super useful, that will be the next step after I install the sash.
Thank you, mate

Abromination - 19-7-2019 at 09:55

The first baffle and lighting has been installed and I have decided on what blower I want. I know that in professional labs that the blower is connected directly to the outside plenum, but is this better then installing it directly onto the hood body?

I put some regularly used equipment in to get a better feeling about space inside of the hood.

Next project is the sash and the control panel.

86597E17-CA31-4840-87F9-EAFC755C0748.jpeg - 2.2MB

CouchHatter - 20-7-2019 at 09:16

Looking good Abromination! Though I fear for that sep funnel's life, never seen one held that way:P

There is a chapter about duct work... I think ear comfort, multiple hoods, and vibration are why it's done that way professionally. The most important reason I can think of, though, is so that there's no positive pressure in your duct.

Having the blower directly after the hood means that any tiny hole or crevice in the duct after the blower will push air into the room and not be exhausted.

Having the blower as close as possible to the end of the duct means that everywhere before the blower is under suction, and that even if there are small gaps in your duct, it will only imperceptibly lessen your air velocity.

As long as you're certain that everything after the blower is airtight, and are certain the dB levels won't be an issue for constant use, and don't set loose things in the hood that might vibrate around, I'd say it's an option.


Abromination - 20-7-2019 at 13:54

Quote: Originally posted by CouchHatter  
Looking good Abromination! Though I fear for that sep funnel's life, never seen one held that way:P

There is a chapter about duct work... I think ear comfort, multiple hoods, and vibration are why it's done that way professionally. The most important reason I can think of, though, is so that there's no positive pressure in your duct.

Having the blower directly after the hood means that any tiny hole or crevice in the duct after the blower will push air into the room and not be exhausted.

Having the blower as close as possible to the end of the duct means that everywhere before the blower is under suction, and that even if there are small gaps in your duct, it will only imperceptibly lessen your air velocity.

As long as you're certain that everything after the blower is airtight, and are certain the dB levels won't be an issue for constant use, and don't set loose things in the hood that might vibrate around, I'd say it's an option.



Don’t worry, it’s quite stable and easier to manipulate with the clamps I have, there is a wide joint at the bottom :)
I will be putting the blower on the end of the duct, which will also help with noise. Thanks again for your help!