# Extractor fan for spray booth Heeeelp?



## seaco (19 Jan 2009)

Hi All

Today we have been mostly making this small spray booth with an 8" extraction fan, we tried the fan before fitting and it worked trouble is now it's finished and run for longer the fan starts slowing down to a crawl so we think it's kn*ckered...

now I've read up on fans it seems that we need something that is explosion proof eeerm, yep makes sense does anyone have any ideas what we may be able to use in place of this fan I have looked and can only find an explosion proof fan at WAIT FOR IT £652 yep £652... :roll: 

There must be a cheaper way, gentleman over to you?... :wink: 

My mate showing how pi**ed off we both are... and yes he is trying to shoot it with a drill???







Closed up...


----------



## bluezephyr (19 Jan 2009)

I dont know much about explosion proof fans, But if a mist of paint is running past electrics it cant be too good for it. That fan wont really pull alot through it and without a filter it will get caked up in no time.

The chaps in the unit next door to me use a machine mart cheap extractor with ducting and welding hoods to get rid of welding fumes, This might be the way to go, Good suction and the mist/fumes dont go over the electric bits, Just over the vanes.


----------



## Chems (19 Jan 2009)

In this the guy just puts a cardboard box with holes in over the fan to stop the main spray getting into the fan.


----------



## seaco (19 Jan 2009)

Hi Chaps

Sorry forgot to say we will be putting a filter of some sort over the fan but this of course doesn't stop the fumes?


----------



## Digit (19 Jan 2009)

Use a centrifugal fan with the motor outside the duct.

Roy.


----------



## seaco (19 Jan 2009)

Hi Roy

Just had a look and there's so many versions could you send a link of the type you mean please?


----------



## CHJ (19 Jan 2009)

Seaco, as roy says you need a fan unit with a metal impellor housed in its own casing with the motor outside the casing, therefore not in contact with the fumes.

Look at cheap chip extractors or cyclone centrifugal fans for construction method.


----------



## Digit (19 Jan 2009)

They are snail shaped Lee, size depends on how much air you want to move. If the fan you are using moved enough air an old fashioned car heater blower or similar would do it.
Quite often booths are/were lined with thin polythene that was discarded when heavily coated so extraction was/is limited to preventing blow back at the operator. A curtain will also do that.
But as I said, how much air do you want to move?

Roy.


----------



## seaco (20 Jan 2009)

Well Roy, it needs to keep the area shown clear I have no idea what I'd need to do that?

Also I haven't found prices yet but proper ones look as though they are going to be pretty expensive, I can't tell from pics I've seen were the fan would be sited the fan in our picture vents through a 7.5" concrete wall to the outside?


----------



## Digit (20 Jan 2009)

Did the existing fan keep the finish from blowing back? If so that is the fan size you require.
If you go too large and suspend a panel in the booth it will start to swing back and forth, not good when spraying.
Take a look at commercial booths for fan size.
If you have a small chip collector try that out.

Roy.


----------



## mailee (20 Jan 2009)

I might be teaching you to suck eggs here Lee but have you considered a pressurised booth? In a full size spray booth as we use at work there is a slight positive pressure to help keep out dust and contaminants from the booth. The incoming air is at a higher pressure and thus no extractor fan is required as such. Air exiting the booth goes through a smaller vent and the incoming air is forced through a filter. In a small set up it may work by using a large fan pushing the air in and a smaller vent to let out the air. Just a thought to ponder on?


----------



## seaco (20 Jan 2009)

Digit":3bj5tk83 said:


> Did the existing fan keep the finish from blowing back? If so that is the fan size you require.
> If you go too large and suspend a panel in the booth it will start to swing back and forth, not good when spraying.
> Take a look at commercial booths for fan size.
> If you have a small chip collector try that out.
> ...



Roy unfortunately we didn't get to try the fan shown as I said it only ran a short time before slowing to a crawl, I will have to look at other booths to see but I'm still unsure where the Centrifugal fans fit is it inside the shop or out?

Wouldn't a chip collector soon clog up?







mailee":3bj5tk83 said:


> I might be teaching you to suck eggs here Lee but have you considered a pressurised booth? In a full size spray booth as we use at work there is a slight positive pressure to help keep out dust and contaminants from the booth. The incoming air is at a higher pressure and thus no extractor fan is required as such. Air exiting the booth goes through a smaller vent and the incoming air is forced through a filter. In a small set up it may work by using a large fan pushing the air in and a smaller vent to let out the air. Just a thought to ponder on?



Mailee no sucking eggs here mate I'm new to making these booths although I can and have sprayed a fair bit but the company I did it for was very Heath Robinson!

We need to keep the costs down as much as possible, Roys idea of the Centrifugal fan seems good but I'm unsure how it would fit into the setup we have, does your idea mean we would have to almost completely enclose ourselves in the booth some way to produce the positive pressure if so this would be difficult to impossible due to available space?


----------



## Racers (20 Jan 2009)

Hi,

You need to strip the fan down and clean and re-oil the bearings its probably an induction motor with a couple of oil impregnated bearings at each end, if you can't strip it down might just be able to get a drop of oil on them.
I do this with my bathroom extractor and it goes twice as fast afterwards.
Pete


----------



## 9fingers (20 Jan 2009)

Going back to the original question, if your fan has an induction motor then there is no sourch of ignition. keep all the switching well away from paint fumes in a sealed box and you should be OK. In the unlikely event of the fan motor coils burning out there could be a spark but this is pretty unlikely.

Make sure there is not an over temperature cut out swithc burried in the motor somewhere - that could spark.

There is some hope for your vent-axia but a snail blower with enclosed motor would be better.

Good Luck

Bob


----------



## Inspector (20 Jan 2009)

Here are a couple booths you might get some ideas from. These use centrifugal fans mentioned earlier.

http://www.grizzly.com/products/g0532

http://www.grizzly.com/products/g0533

If it were me I would put one of those axial flow barn fans with the self closing louvers in a window with some filters in front and only use water based finishes. Like the one below only bigger.

http://www.princessauto.com/_osn.cfm?CT ... TING%20FAN


----------



## Digit (20 Jan 2009)

If the fan is placed some distance from the the booth any paint will tend to settle in the ducting rather than on the blades, so I would use cheap tumble dryer hose and throw it away went loaded with paint. That way you can position the extractor away from the booth.

Roy.


----------



## seaco (20 Jan 2009)

9fingers":35kcga3v said:


> Going back to the original question, if your fan has an induction motor then there is no sourch of ignition. keep all the switching well away from paint fumes in a sealed box and you should be OK. In the unlikely event of the fan motor coils burning out there could be a spark but this is pretty unlikely.
> 
> Make sure there is not an over temperature cut out swithc burried in the motor somewhere - that could spark.
> 
> ...



Hi Bob

I am completely green when it comes to motors how would I tell if it's an induction motor and as for a over temperature cut out switch, I wouldn't know one of those if I saw one?





Inspector":35kcga3v said:


> Here are a couple booths you might get some ideas from. These use centrifugal fans mentioned earlier.
> 
> http://www.grizzly.com/products/g0532
> 
> ...




Inspector

Those look excellent bits of kit but are going to be well out of our price range!


----------



## seaco (20 Jan 2009)

Digit":29zlhv9k said:


> If the fan is placed some distance from the the booth any paint will tend to settle in the ducting rather than on the blades, so I would use cheap tumble dryer hose and throw it away went loaded with paint. That way you can position the extractor away from the booth.
> 
> Roy.



Hi Roy

Thanks for that info I'm just a bit worried now about giving myself instant sunburn using the wrong type op fan?


----------



## Jake (20 Jan 2009)

What are you going to be spraying? Solvent, or just water-based?


----------



## seaco (20 Jan 2009)

Jake":195jbjr9 said:


> What are you going to be spraying? Solvent, or just water-based?



Hi Jake

It will be both but water based until we can get a proper fan I think!


----------



## Jake (20 Jan 2009)

Hi Lee, - does make it easier and cheaper!


----------



## RobertMP (20 Jan 2009)

I extracted using a plate fan in the wall when I did my spraying and it worked really well. In front of the fan I mounted a filter frame which had the innards from an old sleeping bag as a filter. Nothing at all got through to the back of the filter even when it was near to being fully loaded on the face.

Pictures are in my kitchen thread here about halfway down page 2. The filter isn't pictured though.

The first link I turned up on google for the fan was this one -
http://www.mathews.co.uk/acatalog/Single_Phase_Fans.html

Though mine is black it colour it looks similar. I also have the louvre flap cover / guard on the outside.

The filter worked so well I would think allowing the air to stay in the room would not be a problem. I've seen similar filter sold for spraying on ebay.


----------



## 9fingers (20 Jan 2009)

seaco":2k0nxser said:


> Hi Bob
> 
> I am completely green when it comes to motors how would I tell if it's an induction motor and as for a over temperature cut out switch, I wouldn't know one of those if I saw one?



The easiest way of spotting a non induction motor is the presence of brushes - carbon blocks pressing on the a section at the end of the motor shaft.

As for the cut out switch, this would be another device with two wires mounted on the iron of the static (stator) part of the motor in addition to the coils. These could appear on a brush or an induction motor. 

The reason to avoid brush motors is that under normal operation there are a steady stream of small sparks generated.

hth

Bob


----------



## seaco (20 Jan 2009)

RobertMP":j1e6c4wv said:


> I extracted using a plate fan in the wall when I did my spraying and it worked really well. In front of the fan I mounted a filter frame which had the innards from an old sleeping bag as a filter. Nothing at all got through to the back of the filter even when it was near to being fully loaded on the face.
> 
> Pictures are in my kitchen thread here about halfway down page 2. The filter isn't pictured though.
> 
> ...



Hi Robert

I have seen these for sale are they safe to use with spirit vapours as obviously they will get past the filter?




9fingers":j1e6c4wv said:


> The easiest way of spotting a non induction motor is the presence of brushes - carbon blocks pressing on the a section at the end of the motor shaft.
> 
> As for the cut out switch, this would be another device with two wires mounted on the iron of the static (stator) part of the motor in addition to the coils. These could appear on a brush or an induction motor.
> 
> ...



Thanks for the info Bob I'll have to have a look when I'm next there (Monday) and report back!


----------



## 9fingers (20 Jan 2009)

Lee, 

Having thought about it, I'm pretty sure the vent axia will be an induction motor.
Another couple of characteristics of brush motors are high speed and relatively noisy. Neither of which would be desirable for a domestic fan.

Bob


----------



## Digit (20 Jan 2009)

Most vent fans are induction motors in my experience.

Roy.


----------



## Ironballs (20 Jan 2009)

Lee - let me know what you end up doing, I had a brief look into this a couple of months back. I'm considering spraying a guitar myself with nitrocellulose and in the interests of not killing myself with fumes was looking to build a small booth with extractor, came unstuck when trying to find an explosion proof extractor fan that wasn't part of a multi thousand pound booth installation

Reckon if you do it and do it we, there could be plenty of interest on here as a spray booth build how to for spraying solvents

Cheers

Damian


----------



## seaco (21 Jan 2009)

Ok Damian will do...


----------



## BradNaylor (21 Jan 2009)

Possibly too big for your application but my advice to anyone contemplating a spraybooth is to look for a complete second-hand set-up.

I have bought and sold several over the last 25 years or so and have never paid more than £300 for a complete spraybooth including fan and motor. 

Machinery dealers who specialise in buying the entire contents of bankrupt factories are often glad to give the sprayshop equipment away to anyone who will dismantle and clear it.

This is my set up - £300 all in.







Cheers
Dan


----------



## RobertMP (21 Jan 2009)

I'm only a hobbyist now so I don't have to worry about factory inspectors and regulations. The fan I use is not rated for anything more than extracting air. The terminals and motor are fully enclosed though not to zone 2 or whatever the spec should be for flammable vapours.

We had a spray booth in my business though it was for powder coating not wet spray. The fan on that was back behind the filters and was a centrifugal fan (like on a basic dust extractor blower but larger) with the motor external to the booth enclosure. We bought the booth second hand along with the rest of the powder coating plant. The booth was scrapped when we closed the business so I'd agree you might find something cheap at a dealer( or ebay as we sold off most of our surplus stuff on ebay!).


----------



## seaco (21 Jan 2009)

Lovely setup you have there Dan but it's just to big for the workshop we have, I'm wondering if a Vent Axia/ Expelair will draw enough air to do the job?


----------



## Digit (21 Jan 2009)

If your fan will spin freely by hand Lee the motor's knackered, if it won't then the bearings probably need oiling. If that's the case you should be able to try the existing fan.

Roy.


----------



## seaco (21 Jan 2009)

Hi All

Just an update Jake kindly sent me a link to an extractor fan going on Ebay it was bought for a spray booth but never used what do you all think will it be ok I only had a couple of hours to decide so went for it and got it for £27...


----------



## Oryxdesign (22 Jan 2009)

Dan Tovey":tmharof9 said:


> Possibly too big for your application but my advice to anyone contemplating a spraybooth is to look for a complete second-hand set-up.
> 
> I have bought and sold several over the last 25 years or so and have never paid more than £300 for a complete spraybooth including fan and motor.
> 
> ...



Dan do you have an active carbon filter on the back of your booth to remove odours, have you ever had any complaints about smell? Thanks Simon


----------



## Jake (22 Jan 2009)

Why not call Air Vent Technology and see what they say?

Due diligence, as it were.


----------



## seaco (22 Jan 2009)

Jake":nih04jbb said:


> Why not call Air Vent Technology and see what they say?
> 
> Due diligence, as it were.




Just done that Jake and the news wasn't good...  


"Sorry to disappoint, but our fans are not ATEX certified, and therefore unsuitable for extracting potentially flammable vapours.
We don’t supply such equipment, but can point you in the right direction if need be".

Regards

Oliver Behegan


----------



## Jake (22 Jan 2009)

Aaargh, sorry for my part in that, Lee...


----------



## big soft moose (22 Jan 2009)

lee - i'm after an extractor fan to power a home built dust collector. If you dont want that one i'll buy it off you for the 27 notes you paid. I'm in wiltshire so i could probably pick it up depending where in zummerzet you are.

pm me

Pete


----------



## Jake (22 Jan 2009)

Phew, BSM, it sounds like you might salve my guilt for bringing the listing to Lee's attention. 

If not, I think I'd complain to the seller about misdescription if I were you, Lee - but it's borderline - whether by ignorance or design.


----------



## Jake (22 Jan 2009)

In fact, BSM's idea is fantastic, so if that doesn't work out between you and him, I'll step in and do the same (been meaning to make a dust filter for ages).

There are definitely ATEX rated fans listed in the same category (albeit with 3 phase motor, so you'd need a little inverter, presumably).


----------



## seaco (22 Jan 2009)

Jake":g256hu82 said:


> Aaargh, sorry for my part in that, Lee...



No problem Jake mate you weren't to know...


----------



## seaco (22 Jan 2009)

Pete you have mail!


----------



## seaco (22 Jan 2009)

Ok I have found another with an external motor so would be fine but it's 3 phase how easy/hard would it be to convert to 240v?


----------



## Inspector (22 Jan 2009)

big soft moose

Before you or anyone tries the "rejected" blower for a home made dust collector, you may want to check with the maker (as seaco did) to see if it will handle that kind of application. I looks like it is for moving lots of air and would be good in a big air filter for the whole shop but won't have the static pressures needed to move shavings and dust through the duct work from a machine.

Sorry to be a wet blanket.


----------



## DaveL (22 Jan 2009)

I would think you could use this to power an air filter, like this one I made some years ago. 
It is still working collecting the air borne dust in the shop. 
The filters are before the fan so the dust does not get to the motor. 8)


----------



## seaco (22 Jan 2009)

This is the one that will do the job I, think I will have to swop out the motor from 3 phase to 240v though?


----------



## Jake (22 Jan 2009)

Is that the one from a garage?

I'd get a little inverter, the motor won't be huge and they are relatively cheap. Someone was advertising one on here not long ago, dunno if it was the right size or has gone.


----------



## seaco (22 Jan 2009)

Jake":2u1nx9l0 said:


> Is that the one from a garage?
> 
> I'd get a little inverter, the motor won't be huge and they are relatively cheap. Someone was advertising one on here not long ago, dunno if it was the right size or has gone.



Hi Jake I'll have to look into that... as you may have guessed I'm completely green when it comes to motors/electrics


----------



## big soft moose (23 Jan 2009)

lee has apparently managed to reject it with the buyer so I wont be buying this one as my motivation was more to help a forum member out than an urgent need.

on inspectors point I already have a record two fan chip extractor which does all i need in that respect - my extractor fan issue was to power a homemade fine dust extractor like that on some thread or other here. but thats a back burner project for as and when.... (sometime, never  )


----------



## ivan (24 Jan 2009)

The best bet is a second hand booth; but like you I don't have enough room, and as a result have done a lot of research.

A good home made and fold away design can be found at the web site of the US dealer Highland Woodorking's info section. Mine is based on this. The airflow over the whole face of the booth needs to be no less than 2ft/sec. If your (small) booth is only 3x4ft, that's 2x3x4= 24cuft/sec or 1440 cu ft min. Bear in mind the resistance of the filter media will reduce the airflow. For a cheap fan and the folded concertina (see pic above) type filter, the fan will need to pull about twice 1440 cu ft min = 2880 cu ft min in free air (ie. no load)

A 14 inch Clarke plate fan is near this figure, but is not explosion proof. It is an induction motor, but single phase motors have a capacitor which will get hot and smoke (virtually ignite) when it fails. If the blades are steel, an accidental spark may be caused, and organic vapour/air mixtures explode. Your insurance company won't like what you have been doing (the firemen will find you out) and the cost of repair will be all yours, if you survive the bang. Better use waterbased finish, or pressurize your booth _with the fan *outside the room* in clean air_

My folding booth has a face of 2Mx1,8M abd I was lucky enough to find a second hand explosion proof booth fan for 100 quid. However this is 3 phase, like all the other s I have seen.


----------



## seaco (27 Jan 2009)

Me back again, I'm still looking for this bl**dy extractor fan I have come across this one the chap says he's used it for 2 pac paints and laquers etc. and that it's flame proof I'm not so sure it apparently says IP55 on the label and on looking that up it seems to state that IP55 means dust and waterproof, what do ya recon?

It says Sifan I think on it, and on looking them up I can't find any info on this fan!






Label


----------



## 9fingers (28 Jan 2009)

IP ratings and being flameproof/intrinsically safe are not the same thing; although high IP ratings will be associated with safer motors generally.

IP55 is not particularly sealed anyway and the motor has an internal overload protector which means there is a switch inside hence a source of ignition.
There is also a possibility that being single phase, it will have a second switch for the starting winding.

I suspect that certified explosion proof motors will mainly be 3 phase and you will need an inverter to run it on single phase. This is not rocket science and we can help with selecting one once you have the motor. It also will give you variable speed (up and down from nominal) with which to control the airflow should the fan not be well matched to your needs especially one that is too big.

If you want to take a pragmatic approach, then look at motors that are at least ip66 and are not in the path of the paint fumes e.g. a snail blower. Make sure they are also the type that have the capacitor in circuit all the time. i.e. when they switch off you do NOT hear a click of the centrifugal switch.

hth

Bob


----------



## seaco (28 Jan 2009)

Thanks bob

What do you think of this one seems to fit the bill but is 3 phase surely converting it to run on 240v and making it variable speed is going to add considerably to the cost, we are only hobbiests and need the to keep costs under control?


----------



## beech1948 (28 Jan 2009)

seaco,

try following 

http://cgi.ebay.co.uk/A-FERCELL-SPR...PRAYBOOTH_W0QQitemZ370147684239QQcmdZViewItem

alan


----------



## 9fingers (28 Jan 2009)

seaco":suibsf3r said:


> Thanks bob
> 
> What do you think of this one seems to fit the bill but is 3 phase surely converting it to run on 240v and making it variable speed is going to add considerably to the cost, we are only hobbiests and need the to keep costs under control?



One essential thing to look for on a 3 phase motor is the ability to run on 240v. normally the rating plate will say |something like VOltage: 220/415 or perhaps 240/440. This type will be OK
If as the photo shows, 415 only, then there is a doubt that can be resolved by taking the lid off the junction box.

If inside there are 6 terminals usually in two rows of three, then it is very likely to be dual voltage. if there are only three terminals then it is little use for your application.

There are some inverters that produce 440 volts from 240 input. These are more expensive and harder to find.
If however you have managed to pick up a single voltage motor for next to nothing, then clearly there is more in the budget to put into the inverter.

Now to the fan, the one you show is very likely not to be vapour tight because of the belt drive will have to pass through from the motor to the fan. Yes your photo shows a belt guard but the motor shaft still has to get through into the shroud and this is unlikely to be vapour tight.

hth

Bob


----------



## beech1948 (28 Jan 2009)

seaco,

try following 

http://cgi.ebay.co.uk/A-FERCELL-SPR...PRAYBOOTH_W0QQitemZ370147684239QQcmdZViewItem

alan


----------



## seaco (28 Jan 2009)

9fingers":hgcgsgth said:


> If however you have managed to pick up a single voltage motor for next to nothing, then clearly there is more in the budget to put into the inverter.
> 
> Now to the fan, the one you show is very likely not to be vapour tight because of the belt drive will have to pass through from the motor to the fan. Yes your photo shows a belt guard but the motor shaft still has to get through into the shroud and this is unlikely to be vapour tight.
> 
> ...



Hi Bob

I think the easiest will be to swop out the motor for a 240v we have a couple about hopefully one will fit!

If you have seen the original pics I posted here the wall is an outside one so we were hoping to just enlarge the hole a bit then fit the fan to the wall on the outside then box around it with some sort of vent and we would make a grill and filter system of some find inside, could that work?







beech1948":hgcgsgth said:


> seaco,
> 
> try following
> 
> ...



Hi Alan

They look fine but it's all to large and includes a booth which we couldn't use or even remove we only need a fan really...


----------



## 9fingers (28 Jan 2009)

seaco":2slwwwwp said:


> 9fingers":2slwwwwp said:
> 
> 
> > If however you have managed to pick up a single voltage motor for next to nothing, then clearly there is more in the budget to put into the inverter.
> ...



A single phase motor is highly likely to have a switch and hence a source of sparks. Round we go again!

If in your design the fan is only handling clean air ie pressurising the room and the paint vapours take some other route to the outside world then not a problem. If not then there is a risk that you need to feel comfortable with.

There probably is little real risk but we can't tell you that!


Bob


----------



## seaco (28 Jan 2009)

Well Bob we have made as many adaptions as possible (in our money range) to make it all safe so I think we will have to go with the 240v, that's if we manage to get the fan as it looks like it's going to go for a fair bit, if it does go cheaper than we think maybe we will look at an invertor of some sort but with the prices of those I doubt it...

Still it will be better than our original Vent Axia... :wink:


----------



## ivan (29 Jan 2009)

The duct fan in the picture with external motor is the usual explosion proof set up. The 2nd hand one I got was originally supplied by Devilbiss. I got mine for 100 quid, fans alone often fetch 100's, more than complete booth!

The sealing round the belt drive is not always 100%, but provided any gap is on the input side, air will only be going into the duct, not escaping from it. I can't remember offhand the minimum distance for switches (outside the booth) etc from the front of the booth; a single phase motor would presumably also be regarded as safe at this distance as it would be outside the booth, likely round the back. 

I think IP55 motors have a small hole somewhere as a condensation drain, not very helpful (re your plate fan) Blades must be of non sparking material. For a small booth, plate fan could push in clean air if motor on outside of booth. A couple of years back I sprayed a wall of built in wardrobes in situ pressurising the room with a 16" plate fan in window of adjacent room, + fibre filter rigged over door, and spraying room window.


----------



## Boatfixer (29 Jan 2009)

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 (29 Jan 2009)

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 (30 Jan 2009)

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 (30 Jan 2009)

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 (30 Jan 2009)

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 (30 Jan 2009)

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 (30 Jan 2009)

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 (30 Jan 2009)

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 (31 Jan 2009)

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!


----------

