Thank you very much Pete, it will be an interesting reading as I used to work in a HVAC manufacturing company as a CAD engineer. I just want to build a separator, I have a 60l plastic barrel where I would like to have two openings. And I would like to use some fittings to create the required airflow inside. It might not be as good as a cyclone, but I hope it can be done.tiki I take it you are aware of Bill Pentz's site has a spreadsheet that draws up the flat pattern for a cyclone.
http://billpentz.com/woodworking/cyclone/cyclone_plan.php
Pete
Some DYI version of this, as they are no longer in production, but bigger size, as this one is only 20 l