Spray Booth Extraction

[wirey33]

Has anyone had experience of exhausting a spray booth using a wall mounted external fan?

 

I’m looking at the widely available fold-out spray booth and it’s quoted as 3 m3 per minute (180 m3 per hour) and a typical bathroom fan shifts about 85 m3 per hour.

 

I’m assuming that the booth will only be on for short periods of spraying, so this discrepancy in flow rates wouldn’t cause an issue.

 

Clearly I don’t want to overpower the spray booth fan otherwise I’ll end up with no paint on the model and a lot in the filter !!

 

So is this going to be OK? Do I need to find a more powerful fan? Do I even need to extract directly or would the end of the hose placed adjacent to the wall fan be sufficient?

 

As ever, the thoughts and experience of the RMWeb collective would much appreciated.

 

Thanks.

[Paul W]

I use said same foldable spray booth/extractor and I have the end of my booth outlet pipe right against an 85m3 wall extractor, but with about an inch gap between them.

 

By not having it directly connected to the wall extractor this allows for the difference in air movement volume between the 2 fans without over working one of the fans.

 

So far I have had very little noticeable spray mist escape into the room.

 

Hope this helps.

 

Paul

[wirey33]

I use said same foldable spray booth/extractor and I have the end of my booth outlet pipe right against an 85m3 wall extractor, but with about an inch gap between them.

 

By not having it directly connected to the wall extractor this allows for the difference in air movement volume between the 2 fans without over working one of the fans.

 

So far I have had very little noticeable spray mist escape into the room.

 

Hope this helps.

 

Paul

 

Thanks Paul, that's just the kind of info I was looking for. 

 

I'm assuming that the filter on the booth will take out any paint mist and a small amount of fumes would be the only thing coming out of the end of the hose.

 

I would like the the fan extracting air from the room as well as the spray booth hose and your 1" gap clearly does exactly that.

[polybear]

Be very careful with types of motor used, as well as switchgear etc.  Spray booths use brushless motors and enclosed switches in order to prevent (a very real) risk of explosion with (paint) solvent fumes.

 

One reason why they advise you not to use any electrical equipment, light switches etc. in the event of a gas leak

[johnb]

Thanks Paul, that's just the kind of info I was looking for. 

 

I'm assuming that the filter on the booth will take out any paint mist and a small amount of fumes would be the only thing coming out of the end of the hose.

 

I would like the the fan extracting air from the room as well as the spray booth hose and your 1" gap clearly does exactly that.

Watch the air balance in that case, if you are pumping out 180m3/hr from the booth and the wall fan is doing 85m3/hr then I would suggest that with both running, the booth is pumping a net 95m3/hr into the room as the wall fan is only taking part of the output. Obviously it does depend on how long the booth runs for any session but as a rule of thumb I would suggest that the wall fan needs to run around at least three times as long as the booth, to have any chance of clearing some of the excess fume laden air.

 

Air distribution and fume dissipation is a complex subject, so please be aware that the excess booth output is unlikely to stay around the outlet and wall fan, it will 'squirt' in all directions for some distance, whereas the wall fan only draws in air immediately adjacent to itself. Pockets of fume laden air could hang around in places.

 

You might wish to consider to either doubling up on the wall fan, or getting a more powerful one, or ducting the booth output direct to outside. The last option would be my personal choice and recommendation.

 

John

[N15class]

You have to watch an extractor with an inline motor, if your volatiles in the atmosphere become to high the motor could ignite them. I did have a motor on my system a few years back catch fire due to build up on it. 

 

When working we converted our spray booth and room to a positive pressure, much better than extracting through the booth, but rather expensive for domestic use.

[ColinK]

I have the portable spray booth and I used the extractor unit on Sunday for the first time. I simply stuck the end of the pipe out of a part open window. Spraying with acrylics for two one hour sessions and there was no paint smell in the room.

[wirey33]

The room will be in the cellar of a new-build house, so I'm going to specify an extractor for general ventilation and a plain duct through the wall for the spray booth extraction.

 

The general extractor will be switched on when the lights are on, so little or no chance of fumes finding their way back into the room.

 

It's a hobby set-up so I don't see myself spending hours and hours spraying models. It's likely I’ll spend longer cleaning the airbrush than spraying with it !!

Thank you for your input regarding my output :-)

[johnb]

Good planning there. There will be little natural ventilation in a basement, so a full time fan is a very good idea. Even with no spraying going on it will keep the place a bit fresher.

 

John

[wirey33]

I have the portable spray booth and I used the extractor unit on Sunday for the first time. I simply stuck the end of the pipe out of a part open window. Spraying with acrylics for two one hour sessions and there was no paint smell in the room.

 

Could you confirm the inside diameter of the hose? I'll need a plate to mount on the wall to attach the hose to and they come in various sizes.

 

Thanks

[Paul W]

I, like yourself, spend about an hour at a time using the spray booth, maybe on the odd occasion more.

 

Although the output of the booth is rated at 180 M3 per hour, most of this is likely to be "clean air" as I do not continuously spray for the whole hour. I guess this allows the wall extractor to play catch up on the removed vapours via the booth outlet.

 

I accept that there will be some escaping vapour but it is virtually undetectable even without a face mask. I do always use a face mask when spraying and continue to do so for an hour after spraying when I stay in the room just to be on the safe side, as care now will hopefully be rewarded later with no ill health effects due to breathing in vapours. With this set up there is NO smell what so ever when spraying so it seems to be doing what I want it to.

 

This set up works well for me and SHMBO has commented how little smell there is now when compared to before I used the wall extractor.  Basically the only smell is of thinners I have used to clean the airbrush.

 

Just putting the end of the pipe out of a window was my first set up but this is fine on a still day, although I found on a breezy day a lot of the fumes found their way back in through the open window.

 

Also I have found that placing the item you are spraying as far as possible into the booth will reduce the amount of escaping vapours out of the front of the booth.

 

Good luck with your set up.

 

P.S.

 

The inside diameter of the hose from the back of my spray booth is 10cm.