🚀 go-pugleaf

In article <9012211500.AA06021@logdis1.oc.aflc.af.mil> johnboyd@LOGDIS1.OC.AFLC.AF.MIL (John Boyd;CRENP) writes:
In msg:<1990Dec17.015530.17483@bilver.uucp>(Bill Vermillion) quoting:
In article <6606@suned1.Nswses.Navy.MIL> zaft@nswses.navy.mil (Gordon C Zaft)
writes:
In article <9012130133.AA24147@polar.bowdoin.edu> poulin@POLAR.BOWDOIN.EDU (J
eff Poulin) writes:

..My computer came configured with the fan blowing in (presumably to keep
..the stuff in the power supply cool), but I noticed the cards become quite
..warm and one of the hard drives starts sounding like a car going 40mph in

...     Fans on power supplies should never blow into the cabinet, always
..OUT.  The idea is to draw cool air into the cabinet, across the cards,
..through the power supply and out.

..Just because IBM screwed up the original design there is no reason the
..world has to follow.  Fans should always blow IN to a system.  And ideally
..they should have a replaceable filter.

..The problem with blowing out is that the air comes in at ALL entrances to
..the system.  Venturi effects create higher velocities nearer smaller
..openings and you such dirt into such thinks as chip sockets, and worst of
..all THROUGH floppy drives.  That's a killer.

>I had argued this point back and forth with myself for a long time, (no
>snickering B-) ) until I realized that here where I work, the electronic
>assembly 'clean rooms' are ALL positive pressure rooms; i.e. a
>fan/air conditioner blows air from inside the room - OUT - for all the
>reasons Mr Vermillion sited!  Before I changed the fan direction in my
>computer, I had to regularly vacuum my floppy drives and the boards.

I think you will find that if your clean room does indeed blow air OUT
of the room to draw outside air INTO the clean room, then most would say
that the clean room is a negative pressure room...i.e. the air pressure
inside is at a slight negative pressure relative to the ambient air, i.e.
outside surrounding conditions...otherwise how would outside air be drawn
into the room?? Your clean room is basically "evacuating" air from the
room and as the room is not air tight, outside air naturally flows in to
replace that evacuated air...  A postive pressure room would have the fan
blowing INTO the room to cause a slight positive relative to the ambient
air; much like a compressor forcing air into a chamber. Again as the room
is not airtight, air "leaks" out to the outside.

I think that if your clean room is indeed a "positive" pressure room, and
there are some reasons to want that condition especially for manufacturing
or testing where there is a desire to keep contaminants from entering the
clean room, then you may have an auxilary unit pumping air INTO the room
at a rate slightly greater then your air conditioner/fan unit. In that
case, your a/c fan system is simply used for cooling purposes and not to
create the positive pressure....