Russell McMahon wrote:

-snip-


>Using an electrical analog for the air supply, you
>effectively have a "high voltage low current" air supply and you are trying
>to drive a "low voltage high current" device.

Good analogy :)

>  The radial fan comes closest
>to matching the supply. Such a fan when used as an impeller would be driven
>tangentially rather than having the air flow impinge on the flat of the
>blades. I'm nit sure of your exact driving arrangement (in there somewhere I
>know but too many posts in this thread now :-))

Yep.  I have closed both sides of the originally axial fan, and insert the air pretty tangentially, and let the air out in center.

Experimentally found that I got a sligth gain (10%) and less noise if i aim slightly down from original intake, and more to the center.

Reason for not building on an a radial fan are:
More expensive
The fan housing curve is designer for larger flow


>It just may be that you could build.design a unit with magnetic bearings
>inside your budget.

No...

>Real units with such bearings are complex and take
>extensive design effort but in your case the power rating is minimal and
>efficiency unimportant. A magnetic bearing has, of course,  a superb design
>life.

Been thinking of making air bearings, as I already have pressure air, but they will consume some air of course...

/Morgan