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spray booth

2/7/17       
Jeff

i use a 27x13x10 shop built ( not a bought auto booth) spray booth with a Chicago AVS 122 1450 rpm exhaust fan for my woodwork spraying. I have added a make up air unit how does this change the fpm pull and requirements of the exhaust fan? Can some one explain this please. I have horrible turbulence and overspray landing all the way back on the floor to the make up intake. Airflows down both walls with reverse flow in the centre off the booth
Jeff

2/7/17       #2: spray booth ...
rich c.

We'll need some numbers of air flow and size of make up unit to be accurate. Also no idea where the make up unit is located, and if you have internal ducting in the booth to get the exhaust drawing off the floor or just the end of the booth. It sure sounds like you don't have enough inlet to match your exhaust fan.If you have 3 phase on the exhaust fan, you can add a VFD to get variable speed and tune accordingly.

2/7/17       #3: spray booth ...
Jeff

Thanks Ric. The MUA is used so can't read any markings other than it is a ICG 208v single phase. I have the MAU entering the wall on one side of the both at chest level into 20x20 internal ducting that came with multiple register type vents. i have done hours of blocking off restricting partial and have now gone to plugging all and cutting a 20x20 on the right and 20x20 on the left. Exhaust is on the opposite wall of the booth boxed into a 6'x3'x20" filter box chest level.i was told variable speeds on these were not doable . Sorry don't have any other info.

2/8/17       #4: spray booth ...
Bart

Open some doors. You need more air, plain and simple. What is your 1450rpm fan rated for cubic feet per min? To stop the turbulence (negative pressure) you need more available air than outgoing. Gentle is good.

good luck

2/8/17       #5: spray booth ...
Jeff

thanks for your reply. I have a H-Vac guy coming to check it out hopefully soon.

2/8/17       #6: spray booth ...
Leo G

If the airflow is going through the 10x13 area you need a 13,000 CFM fan.

If the airflow is going through the 27x13 area you need a fan that can move 27,000 CFM.

Either way, both are big fans. I have a 18x9 area I'm moving air through and have 17,000 CFM.

2/8/17       #7: spray booth ...
Jeff

Hi Leo Happy New Year to ya. I believe the exhaust is maxed out at 3300cfm and the MUA is at 2500 max i have pulleyed up and down and back and forth to get were it is now . I have heard more than once that over spray is going to happen nothing you can do>> I can't except that .. I spray 5-6 feet away from my exhaust filter bank in what looks like a open booth and the over spray is still getting pulled back over the whole booth????

2/8/17       #8: spray booth ...
Jeff

on line Virtual Air Flow Calculator..CSG Net work.com. So 3510 cubic feet x 45 air exchanges per hour=every 1.3 min. shows 2632 cfm fan required? i think i have the fpm figure of 10x13x100=13,000 but it still list a 3500cfm fan??

2/8/17       #9: spray booth ...
Leo G

100 feet per minute will keep the overspray to a minimum. Some of the corners will have turbulence in them, just the nature of the beast.

2/9/17       #10: spray booth ...
Bart

Velocity of the air is what is killing you. You don't have to spray in a wind tunnel. "If" you had an open back you would empty your booth roughly every minute. You're essentially trying to suck 3000cf of air through 5.5sqft of opening (130sqft back wall if I figure right). That won't ever work. You'll also have to consider your exhaust ducting. Is it impeded or is it a straight shot. If impeded that can create back pressure as well. Expand your intake and spray closer to your exhaust filters. I use the 20x20x2.5 fiberglass filters which grab a lot of the overspray before it has time to bounce. If the overspray is not bouncing violently off the walls it will fall harmlessly to the floor.

good luck

2/9/17       #11: spray booth ...
Bart

PS, If you really want to get into it (I built surfboard sanding rooms in another life) you can get a smoke tester or improvise one to check airflow. A nice even/gentle flow in the right direction is what you want.

I'm done :-0

2/9/17       #12: spray booth ...
Jeff

Thanks Bart i will make the exhaust bank bigger it is the cheapest thing to try .

2/10/17       #13: spray booth ...
Scott

What Leo is saying is the correct design for an open face spray booth. You want 100 cfm per square foot of the opening size to your booth. What diameter is the fan on your exhaust air from your booth? A 24 inch diameter fan is approximately 7000 cfm depending on how fast you have it running. Your Air Makeup has to have larger cfm than your exhaust fan, so for this example you would need a 7500 cfm makeup air.
You want your booth to be in a slight positive pressure. According to the numbers you are using your makeup air unit is to small for your exhaust fan.

2/10/17       #14: spray booth ...
Jeff

Thanks Scott and yes in the perfect world positive pressure would be great but this unit came as a set and used so it was still more than i could afford but the seller got it installed for me and now i'm trying to tune it. I will try and send a video of what is happening . I like the air flow that is moving over the door racks it is a excellent drier just seems the air flow is all intake then when it gets to within 8 feet of the exhaust it just runs out and the exhaust does not take over and grab it to pull it out. I spray right in front of the filters about 5-6 feet away and have built a roof and tapered walls to simulate a open booth in order to help the exhaust grab the flow and keep it moving out.

2/10/17       #15: spray booth ...
Jeff

I spent all day yesterday just baffling the MUA to give me what is now on the video hope you can see it.I will build the exhaust bank bigger today. Then i will do a black spray test with new white sheets to see what the overspray is doing.


View higher quality, full size image (3264 X 2448)

2/10/17       #16: spray booth ...
Bart

Looks like a nice set up. Off the top I'd say some of your intake air is bouncing off the angled walls and swirling a bit. Personally I would extend the fiberglass filters to the floor and to the sides of the exhaust to catch more of the overspray. Mine go floor to ceiling. You'd be surprised how much gets collected. You could put 1/2"x 2" ribs 20" on ctr and staple filters to the walls inside the angled wall in your booth.

cheers

2/10/17       #17: spray booth ...
Jeff

So you can see the video. Shows not available on my screen ? Yes i do love my job but having a more productive booth would make my life a lot easier. I will make the filter area the full size of the wall and the H-Vac guy is coming out today to get real time cfm.....then discuss options. really want to keep that airflow over the the dry racks-fingers crossed.

2/11/17       #18: spray booth ...
chris

buy yourself a dwyer vaneometer. very cheap about$35 measures air speed. very useful.

2/11/17       #19: spray booth ...
Jeff

Thanks Chris i do have a gauge that i have used plus a light piece of thread taped to the end of a stir stick. These are showing me my turbulence i just don't know how to tune it? I have a good demo on video that i have it tuned to now but can't figure out how to get it posted.

2/12/17       #20: spray booth ...
The Staff at WOODWEB

Jeff - if you can send the video file to us or let me know where the file is located, we can try to put it up for you. If it is on You Tube, for example, I can easily put it up here.

The Staff at WOODWEB

2/12/17       #21: spray booth ...
Jeff

sent..fingers crossed

2/12/17       #22: spray booth ...
The Staff at WOODWEB

Here's the video -

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2/14/17       #23: spray booth ...
Jeff

Thank you Woodweb Staff that was a lot of work to get it to work...what a great bunch of awesome people to be apart of .
Jeff
PS. Did a spray test with the setup as is and have some overspray going down half way along the non dry rack wall. Almost there.

2/14/17       #24: spray booth ...
chris

in the photo it shows your table with ducting under it. Is this hooked up to an exhaust fan also?
might be better with a simple stand and the exhaust filters all the way to the ground.

2/14/17       #25: spray booth ...
Jeff

Chris the metal duct is the MUA unit the table is there to hold the quart cans on white paper to show overspray . This baffling on the MUA gives me flow down the wall and also down the centre of the booth up until the edge of my spray test sheet. the air flow at the table on the string shows 2.2mph- then the middle shows 1.2 and then at the entrance door and beginning of exhaust goes to.2mph. The MUA comes into the wall towards the left of the duct at the 20x20 square then deflects left and right. The top ducts and bottom is what gave me air flow down the centre of the booth.. which was completely reversed going right back to the MUA unit with out them.

2/14/17       #26: spray booth ...
Jeff

Sorry Chris thought you were responding to the video. The table is hooked up to a 4000cfm dust collector . I use this as a down draft table to catch any bounce back to the under side of the doors..works perfect. Yes i will take the exhaust filters to the floor.Had a chat with the H-Vac guy and will upgrade to a 6000-8000 cfm exhaust fan with a adjustable speed... wow what a journey to fix what seems as easy as Air In Air Out !!!

2/14/17       #27: spray booth ...
chris

your table with the dust collector doesn't sound too safe to me.
I would do something with your lights too.
Get hold of NFPA code 33.
will give you guidance on spray booth set up and safety requirements for lighting and fire safety.

2/14/17       #28: spray booth ...
Jeff

The table if filtered at multiple places and shows no dust what so ever at the blades at 15 feet away or the plumbing. It was a attempt on grabbing over spray which will not be a issue with a new exhaust fan set up...so i hope

2/14/17       #29: spray booth ...
Bart

Wow that is a loud environment. Not sure what your ducting options are but I would look into a belt driven variable speed fan (30-36" w/sealed explosion proof motor ). Move lots (8-12Kcfm) of air quietly. After watching the video I still think you have a static-negative pressure situation ie..you need more air.

good luck

2/14/17       #30: spray booth ...
Jeff

It sounds a lot louder on the video than real time. I spray with a full fresh air Sata hood setup so all i hear is the hiss of the fresh air.

2/14/17       #31: spray booth ...
chris

determine what size you exhaust filter bank will be. multiply this by 100. This will be the cfm needed for your exhaust.
your air make up needs to be about 10% more.
100 CFM is the required air speed for a booth across face of booth.

2/14/17       #32: spray booth ...
Jeff

My new filter bank will be 6'x6' x100= 3600 exhaust H-Vac figures with filters and piping i'm at 2800-2900ish. Filter bank right now is 6'x3'x100=1800..?I wish it was that easy. I do welcome the reply i'll be damned if this booth isn't going to get fixed!!


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