how "positive" must airflow be for a tower case to keep dust out?

[Jay T. Blocksom]

How would that keep out the dust?? It would seem if any fans are blowing
in, they would bring in dust with the inbound air

[snip]

The presumption is that any/all inward-facing fans would be drawing through
proper washable/replacable-element filters. Most of your better case designs
make provision for this (tho' far too many of them -- including such
"high-end" brands as Lian-Li -- then effectively defeat it by adding way too
many *exhaust* fans, thus making it difficult/impossible to avoid a negative
internal case pressure).

... and any positive air pressure inside
the case would limit the amount of incoming air for ventillation.

[snip]

In theory, perhaps. But as a practical matter, you'll never generate a
significant pressure differential, let alone one sufficient to have a
noticeable effect on this. The cases are just too "leaky".

Don't get me wrong, I would like to see a solution beside airflow limiting
filters since I have cleaned out dustbunnies of record size and number from
a few hundred enterprise computers over the years and I would like very
much to keep the dust out of my new build.

[snip]

Proper filters on the supply fans will never have an excessive negative effect
on airflow *if* two things are true:

1. - The fans (and filters) are properly sized for the task in the first place
(and permitted to run fast enough to do their job, of course).

2. - The filters are kept clean.

--

Jay T. Blocksom
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[Jay T. Blocksom]

[snip]

Dust was the reason the original IBM design, had the rear fans blowing
into the case. The idea was that the intake here was higher, and further
from the carpet/user, and the outflow of air at the front would keep the
floppy disk from filling with fluff.

[snip]

Uhhh... No.

First, "the original IBM design" (in fact, the first *several* IBM-PC designs)
used a "desktop" (i.e., horizontal) case; so the fan was *not* (significantly)
higher than any other part of the system. It wasn't until the "PS/2" line
came along that IBM offered a "tower"-style PC.

Second, the unfiltered inward-facing fan was a product of basically two
factors:

1. - They weren't really concerned with force-cooling any other part of the
system beyond the PSU itself; recall that the CPUs didn't even have passive
heat sinks, let alone active (fan-driven) ones. It simply wasn't an issue.

2. - $$$. This was _the_cheapest_ way to accomplish what they set out to do.

--

Jay T. Blocksom
--------------------------------
Appropriate Technology, Inc.
usenet01[at]appropriate-tech.net

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
-- Benjamin Franklin, Historical Review of Pennsylvania, 1759.
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Unsolicited advertising sent to this domain is expressly prohibited under
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[Dallas]

"Winey"

How positive do I need to keep the case air pressure, to keep dust
out?

I'm sorry if this is already covered in this long thread, I didn't have time
to read it.

I would think anything positive will work, airflow is deciding factor in
cooling. I just used packaging tape to cover every vent opening in the case
and have three fans blowing in and two blowing out. A filter is a great
idea if you clean it once a month. I just went to Home Depot and rigged
something up with some AC filter material. Simple, cheap and works great.

 

[GMAN]

Well, they do. But the other half of the story that's untold there is that,
after making the design, they also learned that people hate having their
computers 'blow' on them.

No, it was the realization that it wasnt so smart to have hot air from the
power supply blow heated air right down on to the cpu.

 

[David Maynard]

No, it was the realization that it wasnt so smart to have hot air from the
power supply blow heated air right down on to the cpu.

No, that was the ATX lesson.