Hey All,
I’m in the process of building a dedicated finishing room in my shop (gloat), and I’m still deciding on how to ventilate it.
My first thought was to use an intrinsically safe axial fan to exhaust the room via a hood. This is the system that I’m most familiar with, and the way things are usually done at most large spray booths I’ve encoutered (like automobile shops). The incoming air is filtered passively.
My next though was, since I often wanted a downdraft sanding table, why not duct the filtered exhaust air from the downdraft table into the finishing room? Provided I can supply enough air, it seems to me that a positive pressure room would be less likely to have contamination problems.
Any advice out there?
Tom
Replies
Positive pressure if you want to keep things out. Negative pressure if you want to keep things in.
Nuclear power plant containments run at negative pressure. (keep any stray radioactive particles from escaping.
Semiconductor clean rooms run at positive pressure. (Keep the dust out...)
Your application sounds like positive pressure.
Mark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
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Most commercial booths run negative pressure and filter the supply air. While positive pressure will keep dust out it won't eliminate the dust created inside the booth by touch up sanding and just walking around. By definition there is no such thing as an intrinsically safe motor. Intrinsic safety means energy limited to the point that bare wires won't arc. If you're going to spray solvent based finishes you need an explosion proof blower motor and a non-sparking blower. Otherwise you're safer sparaying outdoors. And don't forget about the lights too. They have to be explosion proof and operate well below the flash temp of the vapor.
John O'Connell - JKO Handcrafted Woodworking
The more things change ...
We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.
Petronious Arbiter, 210 BC
it won't eliminate the dust created inside the booth by touch up sanding..
Just me... Why would anyone spend all that money for a spray booth and THEN SAND INSIDE OF IT...
I'm missing something????.. Yes,,, time to move it out for sanding... BUT.....
In the (decidedly old school) side-draft automotive spray booths I've been around (25-30 years ago) it was common to touch up primer with a little lacquer putty, wait a few minutes and feather it and shoot more primer. Ditto on fixing little boogers in the base coat. Every time you move a door or a fender you risk dinging it somewhere in the shop, so you end up working in the booth when you get close. This is all usually done by wet sanding, but there will be dust no matter what, even from overspray. Thats why they always wet down the floor with water before spraying and wipe down the piece with lacquer thinner or tack rags right before spraying. This is the big advantage of downdraft booths. When I spray enamel or other slow setting finishes I wet the floor down too.John O'Connell - JKO Handcrafted Woodworking
The more things change ...
We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.
Petronious Arbiter, 210 BC
In the (decidedly old school) ..
I had two helpers working the old Leather Bellows... LOL
lacquer putty! I forgot about THAT! Ya got me!
Edited 6/7/2005 3:55 pm ET by Will George
Well, it does depend on what you plan to use for materials.
Other questions:
1) Where do you live (i.e. climate considerations).
2) Is this spray booth part of an outbuilding, or part of your residence?
3) How heavily will you use the space -- occasionally, every day, etc.
I know nothing about positive/negative pressure, so I can't even ask questions about all that.
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"I tend to live in the past because most of my life is there."
-- Herb Caen (1916-1997)
positive pressure in a spray room will cause contamination to areas outside the room. Neg pressure with passive filters works best for that application, Aloha, Mike
Tom,
About 2 years ago I made a spray room (not for the first time), and used both applications this time. The exhaust fan is set behind a false wall of paper baffles to catch any airborn paint particles before they get blown outside. The vacuum created by this fan is quite strong, in fact it is impossible to open the door to the room if it is running. But I also set up a second unit that sends air into the room. The entire room has a false ceiling of filter material and the second fan positively blows clean air into the room via this ceiling. With both units running the net effect is still a slight vacuum in the room. There is a steady and predictable flow of air down from the ceiling and towards the baffle. I might add that the adjoining room is also "clean", and I use it as a station for what goes in and out of the spray room. Since we spray a large quantity of stuff it is essential to have a clean area for drying what just got done while new material goes into the room.
For huge sums of money there are professional set-ups available, but I am getting excellent results from this homemade room.
DR
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