Vince Pitelka on wed 4 jan 06
Charan wrote"
"Now I am thinking of making my spray booth 2x2x2 feet and attaching the
suggested high cfm fan on its side (with the furnance filter to catch the
glaze) and attaching the outlet of it with a "T" junction to the kiln vent.
"
Charan -
Sorry, but this is a very bad idea. There is too much chance of kiln fumes
bleeding back through the spray booth, or spray dust coming back through the
kiln vent. And besides, a 3" vent will never be enough for any kind of
spray booth. For any sort of effective spray booth, you need a high volume
of air moving easily. Generally, a spray booth fan has a self-closing
shutter on the outside of the wall (opens by the pressure of the fan, closes
by gravity) to keep the winter winds from coming in, and the hole through
wall is at least 12" square.
For a spray booth, you are best using a vane-type snail-shell or axial
blower rather than a squirrel-cage blower, because the latter gets clogged
too easily. I am away from my office and my Grainger catalog, so I do not
have access to information about the specific blower. You might want to
just call Grainger and talk to them about it. Tell them that you want a
blower that won't clog from overspray. Use a furnace filter at the
spraybooth outlet (before the blower) and change it frequently, but you
should STILL avoid using a squirrel cage blower.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Charanjiv Sachar on wed 4 jan 06
Hi all,
I have been trying to send this message since last week of December but because of problems at the clayart server it hasn't gotten through. In case this is a repeat, I apologize.
I have been researching on making a spray booth in my studio. Currently I use a HVLP Harbor freight spray gun that works like a charm and I plan to continue using it.
Also I glaze outside wearing a mask with proper filters and placing my pieces in a big plastic tote box (sitting on its side) so that I don't get glaze every where else.
The problem I am facing is that I live in Washington State where it rains a lot. My schedule for glazing is always getting thrown off because of rain and I am tired of it. So time to build a spray booth.
From all the archives that I read reagrding this, I see a 400cfm to be sufficient for a 2 feet by 2 feet booth. I am still very confused on squirrel cage vs the other fans. On Grainger.com I saw a fan model number 4C445 with 495cfm,.. is this the one to buy?In size it seems small as the inlet diameter is just 5.75inches. Would this be sufficient to capture the overspray glaze for a 2x2x2 feet spray booth? Any clarification on that will be very helpful. If anyone could suggest model numbers from the Grainger catalog that will be great.
My other question is regarding venting it outside. I already have a hole made in the wall where my L&L kiln vents out (3" round). I do not wish to make another hole in the wall for the spray booth. The current set up is the vent goes from the bottom of my kiln towards the wall, turns up 90 degrees and at 4feet turns 90 degree again going to the fan (~130cfm) mounted on the wall exiting outside.
Now I am thinking of making my spray booth 2x2x2 feet and attaching the suggested high cfm fan on its side (with the furnance filter to catch the glaze) and attaching the outlet of it with a "T" junction to the kiln vent. There might be a way for me to either have the spray booth vent open when I spray or the kiln vent open when I fire. So essentially when I spray I will have the spray booth fan on and the kiln vent fan on and the vent section going down to the kiln closed. And when I fire the kiln, I close the vent going towards the spray booth and have only the kiln vent fan on. I will be doing either firing or spraying at a time which is fine.
Does this all make sense?
In my mind i think it should work fine. Has anyone else tried something like this? Does anyone have suggestions why this will work or will not work? Also are there somethings to close and open the vent sections? Haven't found anything at Home Depot.
Thanks everyone
Charan
Creative with Clay
Federal Way, WA
Tel: 253 241 2245
Email: creativewithclay@yahoo.com
www.creativewithclay.com
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Kathi LeSueur on wed 4 jan 06
Charanjiv Sachar wrote:
> Hi all,
> I have been trying to send this message since last week of December but because of problems at the clayart server it hasn't gotten through. In case this is a repeat, I apologize.
>
> I have been researching on making a spray booth in my studio.>>>>>>
>
The absolutely best spray booth I've ever seen is one designed by Bill
Campbell. He had an article on it in Ceramics Monthly years ago and I'm
sure it would be possible to get the plans. If Bill is still monitoring
the list he could probably tell us all the issue it was in.
Kathi
Dave Finkelnburg on wed 4 jan 06
Charan,
You have obviously thought this through and have some good ideas. Good for you for venting your kiln and using a good dust mask with filters!
Your blower seems OK for size but your 3-inch duct is really too small for what you want to do. You want to design for about 100 cubic feet/minute (cfm) face velocity on the booth, as you have, but about 4,000 feet/minute (fpm) conveying velocity in the duct. If you use a 500 cfm fan you'll have more than 10,000 fpm!
Actually, what will happen is you'll have excessive pressure drop and lose flow and you won't achieve the face velocity you want. Depending on the sort of fan, you my have less than half the air flow you want. :-( A small duct will be very noisy besides cutting air flow. By the way, if I misuse the words blower and fan here, please forgive my ignorance...I'm no mechanical engineer.
I prefer the squirrel cage type fan. It is designed to move air even against a higher pressure drop. Axial flow type fans (look like a boat propeller) are inexpensive but are very sensitive to pressure drop. They are designed for clean air that will be unrestricted (by a duct or a plugged filter, for example). Also, with the squirrel cage fan the motor sits out in the clean air, and usually the bearings do also, and only the cage (fan) is in the duct. An axial flow fan needs to work with very little or no duct at all.
Good potting!
Dave Finkelnburg
Charanjiv Sachar wrote:
From all the archives that I read reagrding this, I see a 400cfm to be sufficient for a 2 feet by 2 feet booth. I am still very confused on squirrel cage vs the other fans. On Grainger.com I saw a fan model number 4C445 with 495cfm,.. is this the one to buy?In size it seems small as the inlet diameter is just 5.75inches. Would this be sufficient to capture the overspray glaze for a 2x2x2 feet spray booth? Any clarification on that will be very helpful. If anyone could suggest model numbers from the Grainger catalog that will be great. I already have a hole made in the wall where my L&L kiln vents out (3" round). I
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Maurice Weitman on wed 4 jan 06
At 4:35 PM +0000 on 1/4/06, Kathi LeSueur wrote:
>The absolutely best spray booth I've ever seen is one designed by Bill
>Campbell. He had an article on it in Ceramics Monthly years ago and I'm
>sure it would be possible to get the plans. If Bill is still monitoring
>the list he could probably tell us all the issue it was in.
Bill's article is in the November 1992 Ceramics Monthly.
I agree with Kathi that the design is elegant and preferable to a dry
filter "booth," but it's too much engineering for my Phase I booth,
details of which will be forthcoming shortly after it's together.
Dave "I'm no mechanical engineer" Finkelnburg gave good advice, as
usual, and despite his superior reasoning and all the facts
supporting his opinions, I chose an axial fan with no ducting.
Details at 11.
Regards,
Maurice
Vince Pitelka on fri 6 jan 06
Charan -
A portable spray booth is a good idea, but ducting the exhaust only five
feet outside the studio door is not adequate if the rest of the door is
still open, because the negative pressure created by the spray booth (or any
little breeze outside) will draw the overspray back into your studio. You
really want to avoid any chance of breathing ANY of the overspray or letting
it settle on any surfaces inside your studio. As I see it, the only way to
use a portable spraybooth vented through the doorway would be to have it
ducted through an opening in the door, with the door otherwise still closed.
It would be a simple matter to make a closeable opening in the door - far
easier than making an opening in the wall.
Your exhaust fan should be located right at the spray booth. It will push
air much better than it will pull it in a duct. Also, your reasoning about
putting the fan at the end of the duct doesn't make sense. If there were
holes in the ducting, you would loose your suction through those holes, and
the spray booth efficiency would be compromised.
If you do any appreciable amount of spraying, it really is worth it to have
a permanent built-in spray booth. You want to make SURE that the spray
booth is very efficient. It really is not such a big project to cut a
proper opening in the wall. If you are worried about the space, my January,
2003 Tooltimes column in Clay Times explains how to make a spraybooth that
folds out of the way when not in use.
Keep in mind that any spraybooth exhaust fan requires what is called
"make-up air." In order for the exhaust fan to efficiently exhaust the
overspray, there must be a corresponding amount of air entering the studio.
In cold weather this is a serious issue, and usually requires a heater
working on overtime while you are spraying, but that's preferable to working
outside.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Charan Sachar on fri 6 jan 06
Thanks everyone for your responses. Thinking about it further I sure think
it is not a good idea to have a 495cfm fan blow into a 130cfm fan. I think
because the 130 cfm will not be able to handle the high velocity it will
eventually burn out.
Because I don't have any window in my studio except for sliding doors I
think I will need to fabricate a portable spray booth which is on wheels.
I could slide it to the open door and direct the exhaust 5-6 feet away
from my door to avoid the spray coming back in. It will take some set up
time everytime I want to spray but atleast I can get some work done.
One thought crossed my mind based on the vent-sure venting system I got
with my L&L kiln. Would it be wise to have the ehaust fan at the end of
the duct rather than at the booth? I know many designs say to have it as
close to the booth. But wouldn't it be a better idea to have it away, in
case i have holes in the duct which might bring the exhaust back in the
room. Would the suction drop significantly if the fan was.. say 5 feet
away?
Thanks
Charan
www.creativewithclay.com
Jennifer Boyer on sat 7 jan 06
Are you sure the correct cfm for a 2 ft sq booth is 495? I researched
this about 5 years ago on Clayart. I was making 2 spray booths for a
Steven Hill workshop I was helping organize.
I may have been using the following post from the archives as a
guideline:
is a much better choice for a spray booth than the attic fan. The attic
fan looks a little like a boat propeller. It moves a lot of volume, but
if there is any restriction to flow, such as a filter to remove glaze
particles, and the filter begins to plug, then the flow drops off very
dramatically! :-( The squirrel cage blower, on the other hand, will
tend to be able to move almost as much volume even as the filter plugs
off some. This ability of the squirrel-cage blower to move volume
despite an increase in system pressure drop is why the blower is the
better device in this application. For a great, simple explanation of
this see Figure 2 at this site:
http://ianrpubs.unl.edu/farmbuildings/g1243.htm You do need to know,
however, whether you have enough capacity with the blower for your
particular spray booth. To tell that it would be best if you could get
a blower curve for the particular blower. In the 15th Edition of the
book, "Industrial Ventilation" by the American Conference of
Governmental Industrial Hygienists, the recommended flow rate for a
spray booth is 150 to 200-cubic feet per minute per square foot of open
area. That means the velocity of the air being pulled in across the
open face of the booth should be 150 to 200-feet/minute, even if the
filters are dirty. The higher figure is for openings up to 4 square
feet, the smaller figure for larger openings. All the best, Dave
Finkelnburg
>
Anyway I came up with 1000-1200 cfm as the "going" rate of cfm for a 2'
by 2" by2 ft booth using a propeller type fan. Other posts discouraged
the use of squirrel cages. I found a fan in
http://www1.mscdirect.com/cgi/nnsrhm with a closed motor housing made
for dust and fumes. My booths had 4 sq foot openings so 4 x 200 is 800
cfm needed and I added 200-400 cfm to make up for any inefficiency from
adding a furnace filter to the booth in front of the fan.
Hope this helps
Jennifer
On Jan 4, 2006, at 12:12 PM, Charanjiv Sachar wrote:
> Hi all,
> I have been trying to send this message since last week of December
> but because of problems at the clayart server it hasn't gotten
> through. In case this is a repeat, I apologize.
>
>
> From all the archives that I read reagrding this, I see a 400cfm to
> be sufficient for a 2 feet by 2 feet booth. I am still very confused
> on squirrel cage vs the other fans. On Grainger.com I saw a fan model
> number 4C445 with 495cfm,.. is this the one to buy?In size it seems
> small as the inlet diameter is just 5.75inches. Would this be
> sufficient to capture the overspray glaze for a 2x2x2 feet spray
> booth? Any clarification on that will be very helpful. If anyone could
> suggest model numbers from the Grainger catalog that will be great.
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Charan Sachar on sun 8 jan 06
Hi Jennifer,
I came to my cfm value by hearing 100 cubic feet velocity. So in my case
it was 100x2x2 = 400cfm. Thats why I thought 495cfm should be sufficient.
Also seeing that several ready spray booths like Sugarcreek had 400cfm fan
for a slightly smaller 2x2 feet booth, I assumed it should be sufficient.
Like you there is a good chance I will go for a much higher cfm fan like
800+. As for the kind of fan, the archives and the emails I received are
either supporting the propeller kind fan or the squirrel cage, for the
reasons Vince mentioned in his post and like the one you mentioned in your
post.
I have start from scratch now...
Thanks
Charan
www.creativewithclay.com
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