Powder Coating Painting Booth Extraction

[DiamondDave]

Hi All,


I've been working on an extraction problem with a powder coating booth.

What is meant to happen is the fan should create strong air flow through 3 concertina filters, where the filters trap excess dust and the air just goes to atmosphere.

What is happening is there is a very low air flow and thus very little "suction" I've checked the duct and it looks clear, I've checked the direction of the motor, tightened the belts to make sure its not slipping and checked the fan and motor for lift and bearing wear. I Don't know what else to check that would cause such a massive reduction in suction.

The operators said after I tightened the belt it seemed marginally better but still not the norm.

The only other things I could think of was reversing the motor anyway incase its not marked correctly and I ordered a new double filter instead of only a single but on sliding the filter out of the way and creating an opening you still don't feel any kind of suction.

There also seems to be a bit of turbulence within the booth which the operators said only started happening recently.

Cheers, Dave

 

[hydroman247]

Surely if the motor was spinning the wrong way, it would blow the air the other way?

Do you have a leak somewhere along the extraction chamber?
Can you see any signs of slippage on the belt?

 

[DiamondDave]

Hi Hydroman thanks for replying


I think if motors turn the wrong way a lot of flow is lost but I do believe they still move air in the right direction(just very badly)
. I think this is due to the shape of the blades. This is whats making me think that changing motor direction might work however it would be going against the direction that is marked on the fan blades.

I can't see any leaks and the fan(axial type) is pretty much above the area of extraction most of the ducting is on the discharge side. The pulley looks very shiney so i'm thinking there has been slippage and wear and I am going to order new pulleys. The belt itself doesn't look cracked or shiney i'm not sure when they were last changed. I've turned it on and looked at the fan in motion and its going so fast you can't see it, Also there doesn't sound like there is any screaching when its running.

 

[berkshire]

Have you checked the filters?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[DiamondDave]

Filters were ordered by myself mate and another engineer changed them a couple of days ago. The operators said thats when they noticed the sharp decline however having moved them back to leave an open space flow is still pretty poor.

 

[HowDidYouBreakThat]

Is it possible that an adjustable baffle was inadvertantly adjusted while changing the filters, or one of the old filters was dropped into the duct?

Terry

 

[DiamondDave]

Hi Mate, THere was a baffle/throttle system but it has been removed as it was apparently causing too much restriction in flow. There is no chance a filter could have dropped into the duct i'm afraid . Is it possible I've overlooked something i've already checked?

 

[HowDidYouBreakThat]

most of the ducting is on the discharge side

If the air the fan is trying to move has nowhere to go, you won't get any suction. Check for obstructions in the discharge path. I've seen birds and other critters nest in roof vents. Since the sharp decline was noticed after changing the filters, it leads me to think that something happened, i.e. moving a baffle, dislodging an internal support, or even dislodging a large quantity of accumulated dust at one time and plugging a screen on the discharge point outside the building. I had something like that happen once, except the fan was running and the top half of my body was in the discharge path.

Terry

 

[Compositepro]

It sounds lie the "wrong" kind of filter was installed. Axial fans have very low pressure capability and therefore are rarely used with filters. I've never seen an axial fan used on a paint booth. Normally centrifugal blowers are used to overcome the higher pressure drops caused by filters. Blowers will blow the same direction but with greatly reduced flow if they are reversed. Blowers can also be packaged to fit in-line in a duct so they look like axial fans. If you do, in-fact, have an axial fan then you can only use very open filters that will capture very little dust.

Solving your problem would be extremely simple for anyone who knows what they are doing and knows what they are looking at.

 

[berkshire]

Composite Pro,
Axial fans are used in spray booths because they give very high volume flow, however they do not create much static pressure, the filters used are either a very low drag type called " Paint Arrestors" or the very deep, also low drag Concertina filters, which can hide dirt and dust. One of the tests with a concertina filter is to lay it inlet side down, and Shine a light up through it from underneath. If you cannot see light it is plugged, An alternative lower maintainence item is the non woven roll up screen activated by a differential pressure switch.
Dave,
You said that on sliding a filter screen aside, you did not feel any extra flow, that either means your filters are super clean and the filtered area is more than adequate for the fan , or you have a blockage downstream ,as How Did you Break that said. Do you have a differential pressure guage like a Dwyer Magnahelic between the booth and the plenum to see what your actual differential pressure is?
B.E.


The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[DiamondDave]

Hi Again guys, thanks for replying


HDYBT- The ducting is about 3 foot wide at least and I had alook up it to see if it was clear, it has a slight angle in it but I could see that half was clear and there is nothing for anything to land on beween the discharge and the fan itself. I will need to get onto the roof itself and look down to see that the whole thing is clear.(i'm on backshift just now so that wont be for another week I'm afraid)


Berkshire- I'm afraid we don't have anything like that my department isn't very well equipped. I'll try to check the ducting again for a blockage when i'm back on the dayshift. The only other thing I can think of is its because I ordered a filter with two layers of felt material instead off one as the operators said that the single didn't catch enough powder. However as I said it didn't seem to improve after sliding it out the way.

composite pro- all our powder coating plant and spray booths are equipped with Axial fans fitted by manufacturer.

 

[HowDidYouBreakThat]

There also seems to be a bit of turbulence within the booth

If I understand correctly, the air flows from the booth to filter to fan to duct to outside. Where does the booth air supply come from? I imagine it is filtered as well. What happens to the air flow when you prop open the booth door?

Terry

 

[DiamondDave]

The booth has 2 open doorways at either end so that a conveyer can bring the jobs through there is also a door directly opposite the filters that is shut.(this door was a modification to the set up put in by a new shop manager without consulting our department) I've tried opening that door to see if its restricting air flow but there is no difference. There is no filter or mechanical air supply to the booth.


I've done a drawing but i'm not sure how to upload it onto the site. You are right what you are saying though air at atmospheric pressure should be drawn through the filters which should catch the dust the clean air should then go through the fan/ducting to outside.