• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

SOLVED Positive or negative case pressure....

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.
K

Kryten

Guest
I have seen arguements for both sides in here but the question that still haunts me is ... the difference typically recomended is around 10-20% If we were to use a typical figure of 150CFM this would equate to 15-30CFM, now if the difference was at the top end (30CFM) this is equivalent to 1x80mm fan, now what I would like to know is with all these extra holes that come in the case (using my tower as an example)
it has in the rear plate 36 x 3/16 holes + provision for 2 x 80mm fans, in the front cover down the bottom it has a slit 4.25' x 1' now with all these holes and only 30CFM pressure difference how can anyone honestly say that the have positive or negitive pressure in their case.
I realease that some of you may have gone to extreme mods to remove all the holes but has the average person claiming negative or positive pressures.
 

dimmreaper

Senior Member
Joined
Dec 16, 2000
Location
home
You can't really have much pressure or much vacuum. But of the two, a little pressure is better IMHO.

With a vacuum you will starve the PSU of necessary airflow, and you suck dust in through all the cracks.
 

Shadow ÒÓ

Mod in Hiding
Joined
Dec 20, 2000
Location
Pensacola, Florida USA
I tend to agree........positive pressure with filters on fans would prevent dust build up. Negative pressure would allow sucking in dust from every nook and cranny.

I'd recommend positive pressure even if it were only 1psi as I had negative pressure once on a normal case with tiny holes in the side plates. beside every hole in my side plate was a small collection of dust on the inner case. yet my intake fans had filters.
 

dgk

Member
Joined
Feb 2, 2001
Location
Delray Beach FL
Never used the floppy disk icon before.

Anyway, interesting thread. The betting favorite appears to be more in than out. But the typical mid-tower case has one fan on the bottom front (in) and the power supply fan (out) and a second fan (out). So, two outs, one in. Not good, is it? That's just begging for another fan (in) but I can't think of where to put it. Or, a major fan in that front bottom spot that is as powerful as the two in the back combined.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
It doesn't have to ba a major difference. There are plenty of fan cfm to choose from. Needless to say, the one on my lower front is the most powerful. In my case, a Panaflo 80mm 47cfm. The upper rear is a Sunon 80mm 36 cfm. The PSU fan gets the leftovers. Just enough positive pressure to wiggle a piece of yarn outside the slits on the removable cover.

Hoot
 
OP
K

Kryten

Guest
I was more interested in if people actually believed they had either, yes your cotton would move about in the case, with either because that is "air flow" both sides of the argument have merit dust Vs heat but really with case holes and little extra pressure /vaccuum do you have either or is it lost to the holes/vents?
 

Fro

Registered
Joined
Mar 14, 2001
the over pressure is to keep the dust out, if ya put filters on all your intake fans and have overpressure, you dont get dust sucked into the little holes. and i found out filters made a world of difference in keepin my case clean, dust off a filter every other week, or disassemble my pc every couple months to get the dust out. under pressure would be fine as long as the case was sealed which isnt likely to happen without alot of duct tape..
 

ken257

Senior Member
Joined
Dec 20, 2000
I use a slight possitive case preasure with filters on the intake. It does keep the inards very clean and my case runs at room temp so as far as I am concerned the argument for preassure doesn't hold water, after all we are only talking about just a little bit more in then out not massive compression.
 

Nagorak

Senior Member
Joined
Dec 19, 2000
I tend to feel that you should just try to equal out the pressure as much as possible. Who knows what kind of problems all of this positive/negative pressure nonsense could cause. The truth is, I kind of suspect if you have anywhere near equal pressure in and out (+-10 cfm) it doesn't really matter. A computer case is not an airtight vacuum. There are cracks and holes, nooks and crannies, etc. Yes, airflow will channel mostly through the fans, BUT no matter what there is going to be some air transfer through the holes/cracks. As long as it's not too much, dust build up will not be a major issue (your output fans should help exhaust quite a bit of it) and heat should not get trapped inside the case unnecessarily.
 
OP
K

Kryten

Guest
Kryten (Apr 26, 2001 04:19 a.m.):
I was more interested in if people actually believed they had either, yes your cotton would move about in the case, with either because that is "air flow" both sides of the argument have merit dust Vs heat but really with case holes and little extra pressure /vaccuum do you have either or is it lost to the holes/vents?

Still seem to be missing the point of the question, which is putting aside any argument for positive or negative and any related side effect, the question remains with all the holes in the case and with little extra pressure (negative or positive) would there really be pressure in the case or is it purely theoretical pressure ( a figment of imagination)
 

Fro

Registered
Joined
Mar 14, 2001
yes, there would be more pressure in the case, as you are adding more air faster than it can be removed. but since cases arent airtight it only builds up so far. and like i said unless yer gonna duct tape every hole crack and crevice in your case yer gonna suck dust in(unless you find a really big nylon legging and wrap yer whole case in it...)