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Old 03-17-2013, 06:10 PM
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Spray booth pit preference?

Single 4" wide grate, or 2' wide grate/2' solid panel/ 2' grate?

Cement being poured this week and I gotta decide very soon.

Thanks.
l_ _ _ _l or l_ _ l l_ _ l

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Old 03-17-2013, 07:22 PM
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I've installed and used both, I prefer the dual pit design with a 2' X 2' H connector (I've boxed in the H connector and used a culvert design, both work) in the center versus the single pit. I seem to get better, more even air flow using the dual pit and with the single pit design it seemed a lot more difficult to balance the booth as far as turbulence goes. With the single pit it seemed I could get rid of air turbulence in 1 or 2 corners and then they would appear in the other corners of the booth. The booth's with the dual pit with respect to balancing, it seemed that the dual pit version stayed balanced longer as well. I've used the smoke test to see how fast the booth clears out, they both seem to be equal to a degree but, as I mentioned, I would seem to get swirls of lingering smoke in 1 or 2 corners and the H pit minimized this problem. The last 3 booths I installed all went with the H pit design and had excellent results with happy customers and clean paint jobs.

It seems people get better, more even exhaust flow and back pressure on a car with an H pipe, why not a paint booth.

Hope this helps

Ray
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Old 03-17-2013, 08:43 PM
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Just curious..Are you guys using upflow or downflow in your booth..

Sam
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Old 03-17-2013, 09:23 PM
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Every booth I've been involved with that has a pit has been a Down Draft Booth. I haven't ever installed or painted in an upflow booth. I've done several semi-down draft booths but a pit wasn't required.

Ray
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Old 03-18-2013, 06:53 AM
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Quote:
Originally Posted by 69 widetrack View Post
I've installed and used both, I prefer the dual pit design with a 2' X 2' H connector (I've boxed in the H connector and used a culvert design, both work) in the center versus the single pit. I seem to get better, more even air flow using the dual pit and with the single pit design it seemed a lot more difficult to balance the booth as far as turbulence goes. With the single pit it seemed I could get rid of air turbulence in 1 or 2 corners and then they would appear in the other corners of the booth. The booth's with the dual pit with respect to balancing, it seemed that the dual pit version stayed balanced longer as well. I've used the smoke test to see how fast the booth clears out, they both seem to be equal to a degree but, as I mentioned, I would seem to get swirls of lingering smoke in 1 or 2 corners and the H pit minimized this problem. The last 3 booths I installed all went with the H pit design and had excellent results with happy customers and clean paint jobs.

It seems people get better, more even exhaust flow and back pressure on a car with an H pipe, why not a paint booth.

Hope this helps

Ray
IF I did a single pit 6' wide and installed a center divider out of sheetmetal down the center with an opening in the middle to form the "h" do you think it would be the same difference as your suggestion?
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Old 03-18-2013, 08:15 AM
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A lot would depend on how much air you have coming into the booth. Think of it as an exhaust system of a car. A car's engine needs back pressure to run properly. When a cross over pipe or H pipe is installed it evens out the back pressure. If you run to large an exhaust pipe or pipes you don't have any back pressure even if you have an H pipe installed and the engine won't run to maximum efficiency.

The amount of air coming into the booth will determine how large your exhaust pit should be in order to have positive pressure in the booth. You want positive pressure inside the booth so that if you open the booth door, air will escape from the booth. A booth is set up this way so that in the event that there are any openings, ie. seals between the booth entrance doors, the man door going into the booth etc., the air is being pushed out of the booth and air is not being sucked into the booth. If air is sucked into the booth, or in other words the booth has negative pressure, the air coming in could have dust and air born dirt particles which in turn could land in your fresh paint job. The larger the exhaust pit the more difficult it is to get positive pressure, the other variable that controls pressure is the amount of air that is being moved by your exhaust fan. The exhaust fan needs to move slightly less air out than is coming in. That's why dampers are installed in the exhaust system in order to balance the booth to a positive pressure mode. There needs to be a balance between the amount of air coming into the booth, the size of the exhaust pit (system) and the exhaust fan.

So in answer to your question, if your running a 6 foot wide pit first of all, it would probably be to large for maximizing positive pressure and the sheet metal divider wouldn't allow enough space for evening out the exhaust flow. In the H pit design, again depending on the amount of air coming into the booth, should be about 2 to 3 feet. In what you described, it would be less than 1/16 of an inch and you wouldn't get the benefit of an H pit design balancing the exhaust flow. One thing that hasn't been discussed is how deep is your pit...this isn't as important as the width, but does have relevance.

If you can give the air flow numbers as to amount of air in versus the amount of air out, I could give you pit dimensions that would suit your specific needs.

I know it can be confusing, but I hope this answers your question. If this is still confusing, let me know and I'll try and explain it in a way for you to better understand.

Ray
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Old 03-18-2013, 04:55 PM
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Ray, I appreciate the help
IF i were to do the 6 ft wide pit, I would use sheet metal screwed to the supporting legs holding the center 2 feet of floor up, there would be a 2' seperation of the legs of the H.

My pit is 36" deep from top of floor of pit to top of floor of booth.
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Old 03-18-2013, 05:21 PM
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The depth is fine, as I mentioned in a previous post, the depth isn't nearly as important as the width. I've read your post several times and I think I understand what your planning on doing. If I'm correct your planning on pouring a 6 foot wide pit...period. Then instead of pouring walls for the H pit design your going to have the H pit made out of sheet metal with metal legs supporting the center section. Is that correct?

If it's OK with you, I'll send you a PM and perhaps we can discuss this further. Just for anyone else that may be reading this thread, I should mention that a water drain at the bottom of the pit would also be recommended.

Ray
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Old 03-18-2013, 07:25 PM
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Quote:
Originally Posted by 69 widetrack View Post
The depth is fine, as I mentioned in a previous post, the depth isn't nearly as important as the width. I've read your post several times and I think I understand what your planning on doing. If I'm correct your planning on pouring a 6 foot wide pit...period. Then instead of pouring walls for the H pit design your going to have the H pit made out of sheet metal with metal legs supporting the center section. Is that correct?

If it's OK with you, I'll send you a PM and perhaps we can discuss this further. Just for anyone else that may be reading this thread, I should mention that a water drain at the bottom of the pit would also be recommended.

Ray
I can either pour a 6 ft wide pit or a 4 ft wide pit, the excavation will allow either.
You are correct about making the pit an H design with the use of tubular steel and sheet metal.
I am going to have a sump cast into the floor, with both the main floor and the pit floor having slope. Be really nice for washout, wet sanding, etc.
I am leaning towards the single 4 foot grated pit due to nothing else but time limitations, 14 hrs until the concrete guy is here .

This is a dream in progress, hope to be able to have it complete by this fall. But that all depends on the ol' wallet

Thanks for the help, OF.
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Old 03-18-2013, 07:50 PM
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Glad to help and yes, both designs work and I understand the cost difference and the H pit is a more costly pit design, metal or concrete. The only thing I disagree with what your planning on doing is .... sanding in the booth. Sorry, I cringe when I hear sanding in the booth...lol.

Ray
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