Downdraft pit opinions?

Downdraft pit opinions?

  • yes double pit is the way to go

    Votes: 0 0.0%

  • no, save the money the single will be fine

    Votes: 0 0.0%
  • Total voters
    0
S

Senile Old Fart

Single pit 4' x20' or double pits 2' x 20' w 2' of seperation between pits (actually a single 6x20 pit with a supported 2'x20' slab poured down the middle). I need to figure out which way to go, the concrete guy is ready to do his thing.

Anyone have an opinion if the double pit is really worth the $$.

Thanks.
 
I went with a single 4'w x 3'd x 20' lg pit with a 3' x 3' side exhaust. IF I had more money I would have went with a double row, but I didn't - don't - and have what I have :)
 
I'm not so sure two is better then one but either way, you have a nicer set up then most of us!
 
Could you post a couple pics? I have been wanting to see how to build a booth.
 
Paul;28237 said:
Could you post a couple pics? I have been wanting to see how to build a booth.
Click to expand...

So have I!

I am just winging it from info I can gleen off the web.
15 wide, 27 long , 9.5 height.
4'w x 3'd x 20'l pit covered with 3/16 x 1 3/16" W4 steel grate, exhausting out the center side.
Exhaust filter fits full length 3 inches under the grating.

30" axial fan will draw air from the pit. 3 ph motor with a vfd controlled by a delta P transducer.

Intake air will be supplied by ??? . I havent found a suitable fan at a decent price yet.

Ceiling will have full grid 2'x2' filters.

Lots of lights, and then a few more, LOL.

Sorry I don't have any pictures showing anything of interest .

Here is a link to a guy building a cross flow booth. http://www.hotrodders.com/forum/home-built-paint-booth-extreme-231177.html
 
It sounds like you have a good handle on it. I have been playing with the idea of building a booth for a long time. Just a matter of money now. Please keep us posted on how you do it. Those leasons learned you will have are priceless. And thanks again for sharing.
 
So SOF, how did the booth turn out? Did you get everything situated the way you want so air flows well? Any pics?
 
No it is not finished, the pit is grated over and there are 3 cars in storage setting in there now. This year the intake ducting and lighting will be going in and hopefully the wall coverings.
Its only a matter of $ and time, LOL.
I do now have the fans (3), 1 motor and 1 vfd, 2 more motors to go and maybe 1 more vfd. Then a whole bunch of light bulbs :)

Here is a pic of the concrete guy finishing the floor. He is standing in the pit, just to his left is where the tunnel from the pit to the outside is located. thicken slab with a lot of rebar in that area.
The floor is poured with 1/8" per foot grade towards the pit.
The pit has a sump poured in one end for water collection . a sump pump will be located in the sump and pump out through the tunnel to get out of the building.
0409131102.jpg
 
You have it looking good. i haven't even started... i need to stop guying cars and invest the money in a booth. Keep us updated with pics. you're doing great!! thanks for sharing.
 
I bought a 5hp single phase 220v motor today for the sweet sum of $100 from a guy on Craigs list. He had bought it for his metal lathe but then he never removed the 3 phase motor is has ,and then bought a convertor for it.

Motor is used, but sure doesn't look like very much, no bad smells in the winding hole. Bearings are smooth and quiet. This puppy will make the 30" axial fan move a lot of air, around 12500 @ 1.0 according to the manufacturer.

Was going to use a 3hp with vfd on the axial fan, but since I acquired a pair of centrigual fans I am going to use 3hp's and vfd's on the intake air and let the pressure transducer tell them what speed to run.
Theory is the 2 fans have a greater output than the axial fan.
IF theory proves out then I will be to go positive or negative in a couple seconds notice, like when someone opens the door while the booth is in use and is a bit negative.
Bam- vfd's speed the intakes up and air is pushed out the open door instead of sucked in
.
2 motors down, 1 more 3hp 3ph and another vfd to acquire.

Worst case scenario the axial draws more than the intakes can put out, a simple recirc duct from the discharge back into the intake with a dampener cures that, and gives the option to add an actuator to the dampener and control it with the vfd brains.

Sure a good thing I have friends that work in the commercial hvac bidness. No way I would know how to program it :)
 
Being able to power the fans on and off from inside and outside the booth makes it easier to get in and out without dirt flowing in through the man door. One home made booth I seen had the main fan switch outside with a simple mechanical linkage rod through the booth wall to operate the same switch from inside with no sparks.
 
Running intake and exhaust fans allows for the pressure differential between outside and inside to be calibrated so that very little inrush will occur when a door is opened. I worked at a place that even allowed the booth to run very slightly positive, which is not legal, but they claimed it kept the jobs cleaner.
 
My intent is to run slightly positive as that seems to be the "best" way from all the reading and talking with peoples. What I have yet to find how much is a "little positive" I m thinking 0.5"wc. That is the same as we ran the office and computer rooms at wastewater treatment to keep the acidic atmosphere from corroding all that expensive stuff up. It was barely noticeable when opening or closing a door.
Opinions ??
 
In my opinion you want the positive pressure to be barely measurable, just enough so that stuff from leaks or door opening isn't going the wrong way into your paint. But I think you know more about it than I do.
 
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