Extractor fan for spray booth Heeeelp?

[Boatfixer]

Do you really need to be using an electric fan at all? Many years ago I used to apply solvent based coatings in confined areas and we used to use venturi blowers for ventilation. These have no moving parts or motors so are safe for use with explosive fumes. You would need a compressed air supply but if you are spaying anyway.... It may well be possible to make one that would work well enough for your small booth using the exhaust from a shop vac to provide the air source thus saving your compressor for the spraying.

I would post a link to the sort of thing I am thinking of but as a first time poster (but long time lurker!) it would only get caught in the dreaded spam trap. Try googling venturi blower though and you will find examples of the kind of thing I am talking about.

Regards, Graham

 

[seaco]

Hi Graham

It's another idea but if they are like these http://www.esafetyinc.com/index.aspx?Co ... oupID=1454 again they are an expensive option...

 

[Boatfixer]

I was more thinking along the line of making one out of scrap mdf..... If I get a few mins spare today I'll try knocking up a model to see if the principle works. They are only a cone with air being blown along them from an airbox round the thin end. Those on your link are capable of shifting huge amounts of air. Something a lot less efficient should still be good enough for your requirements.....

 

[Boatfixer]

A very quick experiment with old scrap to see if the principle works..... An airbox made from an ice cream tub with a bit of waste pipe through the middle as the air intake for the spray fumes and an old cardboard postage tube as the outlet chamber. The moving air is provided by the outlet from my shop vac. I think the holes in the lid of the airbox are too large and it would be much more efficient with a tapered outlet chamber (and everything sealed up much better than with old masking tape) but it did work! It pulled shavings through the plastic waste pipe so air was definately being pulled through the device. If you were to spend more than a couple of minutes cobbling it up I'm sure with a bit of experimentation a working extractor could be home made using a venturi.

 

[seaco]

Boatfixer first thing I forgot to say welcome to the forum next thankyou very much for taking the time to make the prototype of the blower it looks really interesting and I'm back over my friends on Monday and we'll see if we can find the bits about to try a prototype our selves!

 

[9fingers]

Lee,

I've been following Boatfixer's suggestion with interest. I've a gut feel that this input of lateral thinking might well suit the application and be a nice low budget solution. Using a shop vac could be a bit noisy but you are only going to be spraying for a few minutes at a time I would imagine.

If you end up dedication an old shop vac to the project then you can strip away all the vac filters and the drum perhaps to reduce all possible drag in its air inlet to maximise air flow rate.

Hat's off to Boatfixer for knocking up the prototype and welcome to the asylum too!

Bob

 

[ivan]

One further thought. The 1.5 Hp trunking fan above will pull enough air for something like 4 sq M of filter, if your booth is muich smaller than this you would have to slow the fan down either by electronic controller or pulley size. Because the belt runs in a tunnel (part of the explosionproofing) possible pulley sizes may be limited.

One or 2 types of garden vac use their blower + venturi for the vac function. However, bear in mind that if you want a booth face of just 3x4 ft you need to move 1440 cu ft min through the 3x4 ft filter to give you 2'/sec, and that needs a low pressure air mover capable of about 2880 cu ft min in free air, which is quite a lot.....A 14" plate fan is about this powerful, and in free air, indoors, will move anything in the room that's not screwed down. Good luck with your experiments, but it's hard to imagine the pictured device moving enough air.

 

[Boatfixer]

As shown the blower would certainly not move enough air - I was surprised it worked at all! This was just a very quick mock up to try the principle and given that none of the joints were sealed and the expansion chamber was just a straight bit of tube it was surprising how well it did work. I have used commercial versions that pulled 4000 cfm but these did run off a compressor and I'm not sure the small booth pictured would need one quite that efficient......

I too am not sure that this is the answer but it could be fun to find out and is potentially a very cheap way of providing intrinsically safe ventilation. After all these sorts of devices are used to clear mine gases and vent underground fuel tanks.

Graham

 

[ivan]

Hmm, food for thought, then. I can remember seeing one in a boating magazine years ago, designed to vent and cool a pleasure boat engine space. The venturi, about 200mm dia. and 900mm long surrounded the vertical exhaust stack, and the exhaust gasses provided the "air" blast to drive the extraction.

Checked out a V.B.sample by googling: to move about 1500cu ft/min through a filter (3x4 ft booth face) the venturi blower has 1" connection for a 40psi air supply.....looks like a lot of air from a 3hp compressor, could stall the spraygun.... Keep us posted!