The new Nitrox Stick

I sold my 2nd Nitrox stick when I sold my 8CFM Mako compressor, so it is time to create a new one.

(put in lessons learned from other sticks)

Here's a link to the actual filters used in the commercial stick: http://www.maradyne.com/marion/sumpfilters/dual_sump_filter.html

To get extra diffusion, the oxygen is injected into the top of the inner filter and passes into the outer, while ambient air goes from the outside the outer and joins with the drawn air of the inner.  I'm not convinced this is the right design- I guess oxygen is forced into the stream in the space between the inner and outer and is unlikely to exit the unit.  But my previous one simply had the oxygen below the filter intake and accomplished the same thing.  Some thoughts I have right now are I wonder if a fine nozzle (think fuel injector) could help pre-diffuse the oxygen?  Then again, having it pass through a filter element would distribute it well and not have a point source.

Here's a diagram of the dual-element filter.   I've been trying to find one and it seems like a specialty part.  I won't find it on the shelf of any auto-parts store.    Looking at that link, I came up with 'SU-65-SF-32', which is a dual-element, 50GPM filter (no magnet), with a 2" port.  It has 450 in^2 of surface area which sounds pretty darn large.  I found one here for $70.  Why 50 GPM?  Well, each cubic foot is actually 7GPM of fluid!
  Heck, 50GPM is only good enough for a 7CFM compressor.  Upon which I throw out the 'bullshit' flag.  The existing filter for the compressor is 3"x5" cylinder.  That's only 60 square inches of filtration.  Looking at my diesel suburban (6.5L engine), the filter is about 14"x6".

That's 320 square inches of surface area.  Maybe the SU filter is including the inner filtration area, which means it is still going to be bigger than the Suburban.   And let's see what 6.5L of displacement does at 1k RPM....  My calculation shows it as 1700GPM.  Now, granted, I'm not breathing through my air intake, but I'm also not filtering it in my compressor either.  Between the suburban air filter and the little one on the intake of the compressor should be fine.


Now the question to myself is: I see an advantage to a dual-filter design for the diffusion of oxygen.  But why not just put one filter inside of another?  I'm going to see if a big ole filter from say my Suburban and a smaller filter made to fit inside it would work.