[rescue] The best 'rescue' workstation

[Phil Stracchino]

Charles Shannon Hendrix wrote:
> Sun, 01 May 2005 @ 13:27 -0400, Phil Stracchino said:
>>Charles Shannon Hendrix wrote:
>>>Actually, no, it isn't moot.  It still reduces dust if the case pressure
>>>is positive.
>>
>>How?  
> 
> By blowing it back out, and by having fewer dust inputs than a negative
> flow case!
> 
> Come on man... :)

Your argument appears to be based upon the premise that no dust is going
to enter the case via the intake fans.  But if you have more air flowing
into the case to generate positive pressure, it's going to bring more
dust with it, and the air that seeps out through case seams etc. is
probably going to leave its dust trapped on the inside of the case seams
instead of the outside.  :)

For any given dustiness of the air, the more air you move through the
case, the more dust you're going to bring into the case ... period.
Whether you're successful in blowing more of it back *out* again is a
separate issue.  For any specified total air flow through the case, the
only way a positive-pressure case is going to have less dust going into
it than a negative-pressure case is if the air passing through the
positive-pressure case is filtered at the intake.  The negative-pressure
case cannot filter all of its incoming air because the incoming air
routes are not controlled (unless, of course, all possible case openings
are filtered).

*THAT's* where you gain: If you have a positive-pressure case with a
single known, controlled route (or several known, controlled routes) by
which air enters the case, then you have the ability to filter *all* of
the incoming air.  If you *don't* filter those controlled intake routes,
then you're no better off, dust-wise, than a negative-pressure case --
and in fact, a negative-pressure case with its primary inflow filtered
may have less dust coming in than a positive-pressure case with no air
filtration.

Filtration is the key.  It matters not one whit, from the point of view
of dust loading, by what route incoming air enters the case; what
matters is whether that route is filtered.  The advantage of a positive
pressure case, from the dust viewpoint, is simply that you can arrange
to have no unfiltered air inflows.  But if dust reduction is your goal,
you've *got* to have the filtration; the positive pressure alone does
nothing for you.


-- 
 Phil Stracchino
 Renaissance Man, Unix generalist, Perl hacker
 phil.stracchino at speakeasy.net
 Mobile: 408-592-8081