John Bolding
Joined: 23 May 2006
Posts: 281
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 Posted: Fri Aug 11, 2006 6:57 am Post subject: Homemade paint hood/booth |
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| Quote: | From: LarryMcFarland <larry(at)macsmachine.com>
Subject: Economical Low Pressure Air System
Hi guys,
Ive been painting with Hangar 21 AFS water borne system and was getting
along very confidently with a 3M dual filter organic charcoal
respirator, but I made a mistake that could have gone very wrong. I
turned on the exhaust fans in my booth, but due to interference with am
radio reception, Id earlier unplugged the fans at the wall. I sprayed
the trim color on my stabilizer, which took no more than about
5-minutes. Over spray build up was such that I was seriously worried
about effectiveness of my respirator. It has limits for heavy
concentrations. I couldnt smell the paint or fumes, but did feel a bit
dizzy later. That did it! I decided to put an air system in front of my
respirator. After checking what others have done, I made up a hood and
mask system that fits over the 3M Respirator that guarantees fresh air
is the only thing my respirator would have to deal with.
A hood was cut and sewn from a disposable Tyvex paint suit. The legs
were cut off in a radial pattern from the crotch to the armpits and sewn
shut. The zipper was oriented to place the shut-end at back center of my
head. I bought a new face shield and put 1/2-inch Velcro on the outer
edges of the clear shield and across the solid top edge. The Tyvex
face was placed tightly against the sticky side of the Velcro and the
Tyvex inside that perimeter was cut out. Integration of the mask and the
hood only took an hour and a half and the cost was well below equivalent
commercial parts. I also purchased a small portable vacuum and ordered
50-foot of air hose. The hood combination face shield fits over the
respirator and inside the neck of my other Tyvex paint suit. An
accessory hose-fitting relieves excess pressure and reduces to a
3/8-inch hose for inflating things. The small hose extends into the hood
and is supported at my belt. I use Saran wrap on the face shield and its
replaced as needed. The apparatus is comfortable, easily maintains
visibility and still allows a good range of motion for spraying in the
booth. Should have done this in the first place.
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Couple of points before we get to the "meat" of this post.
I'm sure that a lot of you will be using some sort of paint "booth" for your
projects and I'll throw in my nickels worth of experience here in the hope
that it might save someone's bacon. I've made this same post before a
couple yrs ago but most folks don't go back thru the archives and we've a
lot of new listers so hang with me for a min.
To preface this let me first state that in my 35 yr career in the spray
equipment industry I sold/ designed/ installed/ moved/ repaired over a
thousand spray booths along the Texas Gulf Coast. They ranged in size from a
bread box to the largest which housed a C5A. Not trying to impress anyone,
I'm too old for that , just stating this ain't my first rodeo and it isn't
"my opinion", you can take it to the bank.
I have seen HUNDREDS of homemade booths , some of which were the equivalent
of factory made but most scared the hell out of me. (I've also looked at a
LOT of the remains of some of those after a fire/explosion and have
testified as a witness during civil trials)
The overwhelming number of homemade booths use some sort of fan designed for
something BESIDES paint booth operation. A booth exhaust fan has a tunnel
drive which puts the motor(no, it does NOT have to be explosion proof)
outside the airstream, it also has a non sparking blade,usually alum but
sometimes brass.
Think about this , if you use a direct drive fan (with the blade mounted on
the motor shaft)to EXHAUST your booth you are drawing the vapor laden fumes
DIRECTLY over/thru your SPARKING motor. The ONLY reason it doesn't explode
more often is it's too lean a mixture. BUT if you drop your gun or turn over
a paint container or spray a LOT in a small area, or inadvertently point the
gun in the fans direction you are asking for trouble, it makes a BIG
explosion, trust me I've seen the aftermath lots of times. Oh yeah, it
usually kills you.
I'm sure that some of you will argue that you are using a Totally Enclosed
or Explosion Proof (Explosion Proof means something different than what you
might think)motor direct drive and you haven't had any problem and it works
"fine". Yep ,it does 'till the outside of the motor reaches temp over
ignition temp of your paint. It doesn't happen very often as everything has
to be just right but it makes an impressive bang when all the stars line up.
To get an idea how much air is required on a code rated booth to SAFELY keep
the levels down please realize that an automotive booth
(26'longx14'widex9'high)has a fan that completely changes the air every 15
SECONDS. 12,000 Cubic feet per min. plus or minus a little.
To build a SAFER booth, keep ALL the lights outside the walls shinning thru
the plastic (the surface of the bulb is WAY over the ignition temp of the
paint ,unless TOTALLY waterborn) but MOST importantly install the fan to
blow INTO the booth, forcing the dirty air out an opening that is floor
level (nearly all solvents are heavier than air) at the other end.
Every time that Kitplanes or SportAviation publishes an article on homemade
booths I give them this missive and they pee down both legs when they
realize what they wrote, then in a couple yrs they publish another, crazy.
On the paint hood issue I use one a lot now that the paints are so
obnoxious.
Used to when you started to smell the solvent (if using a mask)it was time
to change the cartridges but now a lot of the nasty stuff has poor or no
warning qualities so change them OFTEN. I sold a hood for many yrs that had
no eyeshield, all the air spilled out the front opening ,better view, no
contamination as the overspray wasn't going to swim upstream and enter the
hood but OSHA killed it, typical "Big Brother" mentality. Easy enought to
make one however.
OK ,I've stirred the pot enough in the last 2 weeks, back to lurking.
LOW&SLOW John Bolding
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