Cheap extraction fan for spray booth

[thehomeengineer]

Hi All
I asked the question about advice on an extraction fan Advice on extraction fan .

while Trying to research on the internet if it was feasible or possible to use a blower fan, I stumbled across a bouncy castle blower on eBay for £25, and it was only 12 miles away. So I thought at that price and distance I would take a chance. Could always use it for a blacksmithing hearth if it was no good as a extraction unit. (Or buy a bouncy castle).
On my initial test I think it will work as the suctioning is great. Just need to get a suitable filter and some ducting. Please let me know if you can see anything wrong with this idea. I have a video of the fans suction below.

many thanks
The Home Engineer

[jdurand]

Check for an air path from the motor to the blower, some pull air through the motor and vent into the blower. That could allow fumes into the motor. Other than that it should work.

Of course if you use nothing but water based paint you're much safer than more BOOM type solvents.

[thehomeengineer]

Hi All
I have been researching upper and lower explosive limits for paint booths.

This is my thinking
The area of the booth being 1.2 x 0.6 x 0.6 = 0.432m³ (4'x2'x2' = 16' ft³) and the fan moving 300m³/h (10500 ft³/h) there shouldn't be any issues with the vapours catching alight. I am working on the principle that I would only be able to spray a maximum of 22cc (1.3 cubic inch/h) of paint per hour (which I have never done with an airbrush) so the vapour volume to oxygen should be safe?.

I will also be using a spray booth paint arrestor extract filter media pad 100mm thick (4") filter dimension 300x300 (1'x1') I know this doesn't stop vapour exhausting from the booth.

I am sure there is an expert amongst the HMT community that can tell me if I am correct or not?.

Hope there is an expert amongst us
The Home Engineer

[thehomeengineer]

Hi All
I have made another video of the progress of the extraction for the spray booth.

All comments welcome good or bad
The Home Engineer

[thehomeengineer]

Hi All
i used the extraction yesterday on the spray booth and what a massive difference it has made. The extraction fan works really well and I am able to breathe again. I have read a lot about spray panting and extraction plays a big part in achieving a good finish and to my surprise the improvement to the finish I am getting is amazing as the over spray is removed and a smother finish achieved. This might also be that I have bought a midrange priced airbrush a Badger 200 rather than the low price airbrushes I normally buy and use.
The filter material is also working well as the colour of the green filter is changing to an etched grey colour so is protecting the fan and extraction ducting from overspray and is also a great indicator that overspray is being removed. Before starting I placed a piece of paper against the filter and this hasn’t effected the suctioning to significantly.

[Saltfever]

You would think 10 to 11 complete air exchanges per minute would be enough. But you never know when dealing with flammable materials. Everything has a different explosive air-fuel-ratio. A suggestion would be to get an MSDS for the flammable material you are using and try and determine the air dilution necessary to be safe.

Another thought . . . consider a differential gauge to tell you when you need to change filters. Or, a simple U-shaped water manometer made from clear tubing should work.

[thehomeengineer]

Hi Saltfever
thank you for the reply.
I am very interested in the idea of a differential water gauge to check filter service. I remember along time ago a industrial water filter having a differential pressure gauge to show when the filter basket needed to be emptied. I will research this idea and will see if I can incorporate this into my spray booth system. I would be interested in your views on how you would fit this type of gauge to this type of setup.
i will also get the data sheet for the paint.
many thanks again.

[Saltfever]

You are probably talking about a pressure differential of only 25mm or 30mm of water. Here is a link to a Dwyer differential Magnehelic on eBay. But you probably don't need it. No matter how you run your system you will always have a differential pressure related to the ambient conditions in the shop. If you are blowing you will have a positive pressure and if you are sucking it will be a lower pressure. Wherever you locate your probe will determine the + or -.

A small, clear tube (partially filled with water), bent in a U-shape about 1-2 meters long should work. One end is free to the atmosphere and the other end is inserted into the area you want to measure. Take a reading when the filter is new and the system is running. Mark that spot (the water height) on your clear tubing. As the filter gets laden with debris the pressure will change and the water height will move either up or down. It is up to you to determine what is satisfactory filter life. Its a simple device and costs about $2 but always gives you a visual on the status of our system. All the best.

PS: Found this link that shows a simple u-tube. Since you are dealing with such a low pressure water is all that is needed. You can make this a science project (as you have most likely seen in your research) or it can be a simple visual indicator!

[thehomeengineer]

Hi Salt-fever
thank so much for taking the time to explain and I will definitely look into this.
The Home Engineer