Spray Booth Blower Motors?

[hooknladderno1]

Hey Guys,

Yes, another question... I had built a simple spray booth several years ago using a range hood. It worked okay, but wasn't powerful enough. Eventually, the fan became frozen from the paint going through it. The opening of the booth is 30 inches by 20 inches.

I am now looking to replace the blower motor with something more powerful. I have read that some booths removes between 100-150 cfm, and others recommend 300-500 cfm. I have looked on-line at the Grainger catalog http://www.grainger.com/Grainger/categorie...rifugal-blowers , there are so many choices... I don't have a lot of mechanical knowledge. I know that I should look for a 115 volt power supply, but am confused by the variable listings for the CFM such as "cfm@ 0.000 - IN SP" Also there are several other terms such as "shaded pole, psc, forward curve", etc. Any suggestions and ideas that you may have. Thanks.

David

[niart17]

most of the specs on blower motors are going to be way more information than you need for a spray booth. a lot of the specs are for commercial applications where precise control over suction is required and the performance band showing different values at different rpms is important. the main number you want to look at is the overall CFM. all the stuff about static pressure at so many lb/cu. ft of air density is just baseline numbers letting you know where they came up with their CFM rating. it will change based on air pressure in your area, but that's not that important to you as long as you aren't buying one that just barely moves as much air as you are requiring. where i work, we use a 1.5 safety factor. we take the maximum required CFM and multiply time 1.5 to insure no matter where it's being used it will pull that much. that may be a little high for your needs but it's something to thing about.

i would recommend a blower with the motor outside of the airflow. that's the reason your kitchen vent fan seized up more than likely. we use a company called twin city fans. they are pricey though, at least the commercial grade. i haven't priced a consumer version yet but i will need to soon. hope that helps a little.

Bill

[Aaronw]

I built myself a paint booth this summer, it is a bit smaller than yours 18x24" opening but I also went with a larger than minimum fan for the size. I used a cheap 14x20" furnace filter to catch the paint particles.

The fan I got was a 485 CFM squirrel cage blower from Grainger. The part # was 1TDR7, and it cost $144, plus another $8 for a cord. There was a similar capacity blower for $112, # 1TDR9 at 463 CFM but it has a larger rectangular discharge that seemed like it would be harder to work with.

I found Graingers service to be great, I had my fan delivered to me door step 24 hours after ordering it.

For estimating CFM for a booth it is recommended you have 100 feet per minute for a cross draft or 50 feet per minute for a down draft. You just divide your fan by the sq feet of the opening to determine your feet per minute. I noticed many of the commercial hobby booths fall well short of the recommendation as do many home built booths. The size booth you have should be fine with a 400+/- CFM fan so either of the fans I listed should work.

The different ratings come into effect when you add ducting, if you just have a short straight metal duct for exhaust you are good for the full rating of the blower. If you use flexable ducting, have multiple bends and / or have a long run then there are calculations to figure out what the true CFM is.

I had a good link to an article about building a paint booth that had all this info in it, I'll post it if I can find it again.

[niart17]

aaron is right about adding duct work. then you have to take in to account static pressure. i'll see if i can find the chart we use to find the static pressure for various diameter piping. if you use flexible pipe, the SP values increase approximately X3. the less duct work you can get by with the better you are. of course then the noise level can increase since the motor is closer to you.

another thing you want to be careful of is pulling too much air. i know that sounds contrary to what you want, but if you pull too much then the chance of pulling dust into your paint work increases. the trick is to get just enough to get keep the air flow smooth and consistent.

good luck and i'll try to find those calcs.

Bill

[BOC262]

I built a spray booth based on an article that appeared in FSM. The article compared about a half dozen commercially available booths, ranked them from best to worst, and published their technical specifications. I based my booth on the winner. The original was made of sheet metal, I made mine from plywood. The blower used was a Dayton shaded pole type. Two commonly available furnace filters are used to filter out most of the paint. The booth has been in use for over 15 years now and is one of the best investments I ever made for this hobby. Here's a picture:

Edited October 17, 2009 by BOC262

[Aaronw]

Here is a link to the article I used to help make my booth.

http://www.briansmodelcars.com/tutorials/t...p?TutorialID=23

I built a booth from 3/8" plywood, 24" wide, 20" deep (plus a 4" plenum space) and 18" tall. Bought a clamp on light, a sheet of 1/8" plexiglass to make a closing door for the booth, and the motor I mentioned above for about $200 and a day of work. I used a scrap piece of 3/4" plywood for the back to better secure the motor and painted the inside of the booth with some leftover white latex paint. I angled to front opening so I could paint downward as well as from the front but plan on using the plexiglass and some 1x2" strips of wood to make a folding door so I can adjust the size of the opening as needed.

I've only used it a couple of times so far but it seems to do a good job of sending the fumes outside.

Edited October 18, 2009 by Aaronw

[don weixl]

I built my spray booth using plywood and an exhaust fan that I bought surplus at Princess Auto supply for about $50. I believe it was an exhaust unit from a DC-9! It has an electric motor the size of a furnace motor and sucks like crazy, although it is noisy as a Harrier in a hover (very noisy).

Don Weixl