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Old March 16, 2008, 02:53 PM
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Default Positive vs Negative Pressure?

After doing some reading and going through more worklogs than it takes to make my resent my rig lol I have begun to wonder on the different opinions on positive and negative pressure and just how both are achieved, pros vs cons, basically just everything about it including...everything lol tx for any help in advance
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Old March 16, 2008, 02:59 PM
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positive pressure - pressure in the case is higher than outside, meaning air will be pushing out of every crack in your case. Means the total intake CFM > than the CFM of the exhaust.

negative pressure - less pressure in the case than outside, so stuff is sucked in through every crack and you never need to vacuum again, since your computer sucks up all the dust. Occurs when intake CFM < exhaust CFM

Personally I try for neutral pressure (intake CFM ~ exhaust CFM), because I only care about airflow over my components (and also since too much air insulates, and not enough doesn't keep my heat sinks cool). If you have a really dusty living area (pets) you might consider positive pressure.

Also, in case you never saw CFM before, it is the volume of air that your fans will push. Often this can be found on the manufacturer spec sheet.

I think it is a little pointless to go for +/- system, since cases are all not air tight, but I don't have any numbers comparing the efficacy of either setup.
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Old March 16, 2008, 03:27 PM
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The most obvious factor is that if you have a positive pressure system, all the airflow will enter through the intake fans. This means that it's possible to actually filter all the incoming air. In a negative pressure system, since a portion of the air is being sucked through the gaps and spaces elsewhere in the case, it's extremely difficult to properly filter all the air, which makes it easier for dust to accumulate inside the case.
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