Fredrick Paget on tue 11 may 04
>. Does anyone know if a squirrel cage
would pull air out of a spray booth better than an attic fan? Thanks,
>
>Paul B
The squirrel cage fan will put air through a back pressure or
constriction such as air filters or small ductwork better than a
propeller fan. Propeller fans' air delivery curve drops off fast if
there is back pressure. However if given a good clear path to the
outside air they typically pump more air at the low pressure than an
equivalent power squirrel cage fan.
If you use an attic fan keep the ductwork as large as the fan
diameter or close to it and use a very open type air filter. There is
a washable plastic one that is good. The discharge air will contain a
little spray and the motor of the fan will pull it into the motor
coils so you need to rig a separate clean air duct to the motor. I
found that a 2 pound coffee can fitted the motor and a 4 inch duct
from the bottom side to clean air allowed a good supply of clean
cooling air for the motor.
Fred
--
From Fred Paget, Marin County, California, USA
fredrick@well.com
Paul on tue 11 may 04
i have been using a attic ventilation fan for my spray booth with good
results, but I am going to modify the set up a little, and I recently
acquired a couple squirrel cage blowers which are fairly large and seem
to really blow a lot. They seem to blow air much stronger than the fan I
am using, but it is hard to tell if they will really draw any more air
out of the booth than the other one. Does anyone know if a squirrel cage
would pull air out of a spray booth better than an attic fan? Thanks,
Paul B
Dave Finkelnburg on tue 11 may 04
Paul,
In general, if the squirrel cage blower has enough capacity, it 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
----- Original Message -----
From: "Paul"
Sent: Tuesday, May 11, 2004 3:30 PM
i have been using a attic ventilation fan for my spray booth with good
results, but I am going to modify the set up a little, and I recently
acquired a couple squirrel cage blowers which are fairly large and seem
to really blow a lot. They seem to blow air much stronger than the fan I
am using, but it is hard to tell if they will really draw any more air
out of the booth than the other one. Does anyone know if a squirrel cage
would pull air out of a spray booth better than an attic fan? Thanks,
WHC228@AOL.COM on wed 12 may 04
Use a tubeaxiel fan. This is what is used in professional spray booths.
This is a fan with good suction, and volume.
Squirrel cages are good at supplying air, but poor at suction. It is a lot
easier to blow air than to suck it.
You can get the tubeaxiel fans from the Grainger catalogue.
Bill Campbell
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