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Attn all homemade spraybooth builders; need blower motor advice

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  • Member since
    December 2002
  • From: Modeling anything with "MARINES" on the side.
Attn all homemade spraybooth builders; need blower motor advice
Posted by AH1Wsnake on Monday, January 9, 2006 1:26 PM
Hi guys, I have seen quite a few good designs posted in this forum, and I know that there are some very knowledgeable people here when it comes down to airbrushing and airflow. I'd be in your debt to get some advice on this topic...

I'm looking for some advice on selecting a blower motor for my home-made spraybooth.
It is a cross-draft design with an interior of about 30" wide x 25" tall x 20" deep. The basis for fume extraction is a 20" x 25" furnace filter installed in the rear of the booth. It is very similar to the design specified on this website (click). I just increased the dimensions a little.

I am also using the CFM and static pressure values that the author uses. The trouble is, I really don't know what these values mean, since I have no experience with them. He states 100 cubic feet per minute through the booth as an industry standard. Is this correct? Is this a noticeable airflow?

Back to my specs and the author's guide for calculations.....
Using the 20"x25" furnace filter as the interior size and multiplying by 100 CFM, I come up with a value of 347 CFM that needs to move through my booth (1.67'x2.08'x100). Secondly, I anticipate using around 20 to 25 feet of vent tube, once all the angles are taken into consideration. By using 4-inch duct, I would apparently have a value of around 1.2 static pressure in the ductwork. 5-inch duct calculations yeild a static pressure value of around 0.4 in the ductwork. So, I think I will be using the 5" duct, since I have not seen any motors with specifications beyond 0.8sp.

Ok, boring calculations aside, here's my dilemma. I'd like to purchase a Dayton blower to use as the extraction motor. The author of the article recommends 4C444 and 4C445, as they are listed in the Grainger catalog. Truth be told, I am really stuck between the two. At the 0.4sp I calculated, the 4C444 seems underpowered, and the 4C445 is overpowered when I use the 347 CFM value of airflow. I'd hate to get too small of a motor and have my booth be essentially useless. On the other hand, I'm afraid of getting too powerful of an airflow, and having some sort of swirling vortex inside my painting area.

I'm looking for suggestions from people here who have built their own booth, or from those who have experience with airflow requirements in painting. I'm leaning toward the 4C445, but am just unsure. As far as the blower motor goes, what course of action would you recommend?

 

"There are only two kinds of people that understand Marines: Marines and those who have met them in battle. Everyone else has a second-hand opinion."
  • Member since
    March 2003
  • From: Commerce Twp., MI
Posted by Klaus Raddatz on Monday, January 9, 2006 8:44 PM

AH1Wsnake, the 100 FPM (rather than CFM) airflow through the booth is barely noticeable. Since I wrote the article I've upgraded to the 4C444 blower and 5" duct to get 100 FPM airflow. It works great.

With the limited choices  for blowers a dilema such as yours is not uncommon. Buy a small bower and risk poor clearing of the booth, or go with more power (Rrrr) and risk finish problems. If it were me, I would choose the larger blower and add an adjustable vent to the plenum area of the booth. Try painting with the plenum vent closed first, and if the airflow is causing problems, open the vent a little to reduce the airflow through the booth. IMHO, it's the least risky of the two choices for blowers.

Hope this helps. Feel free to contact me off the board as well (dadsworkbench@msn.com)

Klaus

  • Member since
    July 2003
  • From: Redmond, WA
Posted by bwr1 on Monday, January 9, 2006 9:58 PM

I have a homemade booth similar in dimensions to what you're planning.  My ducting is shorter - probably 10' equivalent.  I have the 4C445 blower, and I find it works just fine with ample flow but no funny vortex action.  I'm also running through a furnace filter (forget the exact size).

For what it's worth, due to location and size constraints I have an updraft venting system, and in contrast to the website mentioned I have never had a problem with it, and it greatly simplified the construction of the booth (the blower just sits on top of a rubber gasket on the top of the booth - its weight forms a fine seal, and if I ever need to get it off for maintenance it just lifts off).

 

  • Member since
    December 2002
  • From: Modeling anything with "MARINES" on the side.
Posted by AH1Wsnake on Monday, January 9, 2006 11:06 PM

Klaus and bwr1, thanks very much for the replies. (Great article by the way, Klaus...I used it extensively)

I will probably go with the 4C445 now. I was a little worried about overpaying and getting too much power; but having the larger motor will as you say, Klaus, allow some variation of the airflow with a plenum vent. The larger motor will probably even give me some leeway as to the length of my exhaust duct, should I ever need to change the position of the booth.

Klaus, I may even email you with some specifics later.

Thanks

 

"There are only two kinds of people that understand Marines: Marines and those who have met them in battle. Everyone else has a second-hand opinion."
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