Axil Flow Fan & booth design questions

S

Senile Old Fart

I bought a new slightly freight damaged 30" axial flow belt driven fan. As you can see in the photo one of the flanges was bent a little bit, nothing 30 minutes wont fix :) $250 cash w/ receipt :)
It was shipped with a 1 hp motor which I will be replacing with a 3hp before it is installed.
It was intended for use on a new Rohner paint booth.
The specs on it are: 1hp 1 ph, 240v.
8000 CFM at .3" SP
IF 3hp
12300cfm@.3" SP





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This will be my exhaust fan, what I am wondering is positive pressure or negative pressure preferd. If positive pressure is the cats meow I will continue to look for a pair of 8000 cfm intake fans.

2nd question, down flow booth, Which is best a pit or "basement" where the floor is lifted 6 inches off the slab . Is the pit type worth the effort of digging and forming or is the basement the easy way with just as good of performance?

Cost difference is not an issue, they are both comparable in that respect.

I am leaning towards the basement type as it would be a heck of a lot easier to remove from the structure someday in the distant future when we push up daisys .
 
Slightly positve pressure-just enough to keep any dirt from being pulled in past the door seals but not enough to cause fumes to go out. If you could design your doors to seal with positive pressure that would be best. What diameter fan is that? I've cleaned some pit booths for regular maintenance and it ain't no fun, I don't have any experience with the elevated floor type. Is your heating system going to keep up?
 
Bob Hollinshead;24343 said:
Slightly positve pressure-just enough to keep any dirt from being pulled in past the door seals but not enough to cause fumes to go out. If you could design your doors to seal with positive pressure that would be best. What diameter fan is that? I've cleaned some pit booths for regular maintenance and it ain't no fun, I don't have any experience with the elevated floor type. Is your heating system going to keep up?
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Hi Bob, it is a 30" diameter.
I have been giving a bit of thought to the door seal and am thinking of ham & egging up an inflatable seal.
Kind of like we have installed in level 4 bio labs, but not $100 a foot!

More on the $.10 a foot price level. Something like a bicycle innertube surrounding the door, then inflate. Need to do a bunch of searching for a "gasket" that would work.

Heating system will be mother nature, will only use it a couple times a year and just plan on summer time. I have a heated garage to do priming in. Booth will be a storage area unless there is a need to paint. I just figure for a bit of extra cost up front I can build this storage shed to be multi purpose.

What was the pit cleaning issue? I would have thought a hose and a small pump set into a sump would make short work of this, what am I missing?
 
crash, the air will enter from outside just above roof top level. (probably use a couple roof top restaurant kitchen exhaust fans feeding into the building instead of exhausting out.)
They will feed into an overhead filter bank app 4' wide x 24' long.

I am thinking about discharging the exhaust air a few feet above ground level after it passes thru a wet wash box which would be mounted on the end of a horizontal run of duct.

All opinions and ideas are appreciated.

I never have had the opportunity to paint in a down draft booth, but the videos and the concept sure look like the way to go. I am designing this by the seat of my pants and hopefully it will work great on the first git go.

While this really isnt practical for the amount of use it will get, it will be nice to have when I want to use it and will provide a much needed storage area the other 360 days a year,lol.
 
Well, even though you propose to use the booth only in summer, it would be much more versatile if some heat could be brought to bear when needed, though with the kind of flow you are planning I suppose the kind of setup I employ would not really work. In my shop, the booth draws air from the shop floor. In the winter, setups like this are intake flow limited by the fact that the shop is sealed up against the cold. This can even pull flue gases the wrong way if the draw is strong enough. My solution was to jerry rig the electric heating element out of a residential air handler over the outlet of an old swamp cooler that is mounted through the wall of the shop The cooler has been retrofitted with spray booth filters and only acts as a blower to lessen the negative pressure in the shop. The element is able to raise the temp of the incoming air by around 40°, which really helps in the winter.
 
SOF, keep us updated on your project. I know of one booth in my area that had water filtered exit air but they converted it to a conventional booth recently. The maintenance cleaning issue in the pit booth I mentioned earlier had more to do with not enough regular exhaust filter changes mostly but the pit sure was a mess and it created a fire hazard with that much paint in the ducts for the bake cycle.
 
Hello SOF, Positive pressure for a paint booth sounds good, but any more than the slightest bit of positive pressure and you lose your laminar flow. Air that is suppose to be going in one side and out the other will be forced in with no place to go but every which direction. The end result is overspray that floats around the booth, drys and lands on the car as dirt specs. My booth (Spray Bake) has two fans....one pushes air in and other sucks it out. A movable flap tunes the pressure. If I forget to adjust for a different car, I see it right away.

I think a booth with intake filters on the ceiling/high on the wall on one end, and the exhaust down low on the other end would give you a "semi" down draft. Alot of intake filter area will help in keeping the dirt from being sucked in in other spots i.e., under the door. If you do put filters on the ceiling, they need to have some kind of cover above them to keep shop dirt from filling them up.

Scott
 
Hi Scott, what to you set the delta p for in your booth?

Dmattingly runs their booths at .2 +/.3 +
dmattingly;23557 said:
they have both. every where I have worked the booths set between .2 and .3 positive pressure on the gauge. some booths the pressures are controlled manually with dampers. computer controlled booths usually have variable speed fan motors
Click to expand...
The fan I just purchased is rated at 8000cfm @.3sp or 12300 cfm @ .3 cfm with a 3 hp motor. That sounds like it should work well in a booth with pressures such as you suggest :)

I am thinking about a damper for pressure control as a freq drive is out of the budget unless I score a freebie.

Would you mind taking some pictures of the system you are using ? thanks!


The air will be drawn in from outside and when not in use there will be gasketed caps on the 2 inlets. I might mention this booth will be used for storage for the greatest part of the year, just painting in it in the summer time.


Crash, it would be nice to be able to afford heat and the cost of running it to paint anytime of the year, but a 1M btu heater is $$$.I can paint in my garage year around . I can heat outside air at the rate of 2600 cfm with a temp rise of 90f (name plate rating, never been real world tested) with the current system I have .

Bob, thanks for the heads up on pit maintainence. I am going to slope the floor of the pit to one end and have a sump at the low corner. Small sump pump will connect to piping to direct the discharge to the outside, either into a 55 gal drum, or if only wash water onto the soil. I was planning on pressure washing the pit after usage and before storing stuff over it so it is ready to go for the next time .





How about lighting, what are the opinions here? horizontal vs vertical ? vertical corner lights? thx.
 
Senile Old Fart;24374 said:
The fan I just purchased is rated at 8000cfm @.3sp or 12300 cfm @ .3 cfm with a 3 hp motor. That sounds like it should work well in a booth with pressures such as you suggest :)
Click to expand...

If that fan is rated at 0.3" s.p. that does not mean that you will have 0.3" positive pressure in the booth. The s.p. refers to the total amount of pressure that the fan can overcome at a given cfm. For instance, your hvac unit at home is circulating air, let's say your house has neutral pressure (0.0"). That does not mean that the fan is seeing 0.0" s.p. It has to overcome the pressure drop across the filters, ductwork, coils, grilles, etc. Same in a paint booth. There will be some amount of pressure drop across each feature of your booth: filters, ductwork, grilles, etc, that must be taken into account.
 
SOF, My booth has a simple analog needle that shows a "good zone". (a little above neutral) The damper is a round plate on shaft in the exhaust duct and it is set manually with a cable like is used on small aircraft throttles. Close it off a little to raise the booth pressure and vise versa. The lower I set the pressure the better the paint job. BTW, my booth uses 2, 7.5 HP moters...one intake, the other exhaust

Scott
 
Slowly coming together :)

Ordered a phase convertor/vfd yesterday.

Now I need to place a call to an acquaintance that works for Trane.
He said once I had the freq drive, then he would know if he has any pressure differential transducers on the used shelf /take out stuff that will talk to my vfd.

Pit is poured and bar grate is here and waiting to be fit, but I need the grandson to help with all the lifting.

Next on the schedule is wiring. :encouragement:
 
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