What is negative/positive pressure for airflow?

tigereye

Senior member
Oct 27, 2000
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I am going to add a fan to my new case in the back, but I want to get rid of the "holes" that they have back there, and just slap a grill on it. What should I use to remove the metal back there? Keep in mind, don't have a dremel.

<EDIT> Changed Title since the cutting situation has been addressed.</EDIT>
 

BassDominator

Senior member
Feb 8, 2001
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Dremel is best for avoiding sharp edges. Borrow one if you can. Otherwise, if you have an electric drill or screwdriver, you can get a bit for it that will do the same job. A small acetylene torch, tiny hacksaw, and tin sheers will also work. Helps to have a metal file handy to clean up the edges.
 

tigereye

Senior member
Oct 27, 2000
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So, I could get a cutting wheel for my drill? Do such things exist?

Also, I assume that even after filing, it will be a bit sharp, should I wrap the edges in tape or something?
 

BassDominator

Senior member
Feb 8, 2001
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So, I could get a cutting wheel for my drill? Do such things exist?

Definitely, just let the folks in the hardware store know what you need to do.

Also, I assume that even after filing, it will be a bit sharp, should I wrap the edges in tape or something?

Tape shouldn't be necessary. Just start filing it down with a rough file and then use a very smooth one to finish it off.
 

tigereye

Senior member
Oct 27, 2000
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Rojas,

Looks ok from the picture, but their website appears to be having problems. I'll keep trying, though.
 

Suppafly

Senior member
Jan 11, 2001
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make sure you remove all your internal stuff before you start hacking on the case.. and get ride of all the metal pieces when you are done.. why do you want to do it anyway? more air flow? maybe itd be easier to just enlarge the existing holes..
 

tigereye

Senior member
Oct 27, 2000
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Well, 2 reasons really. 1, more airflow, that is true. 2, and the main reason is that I want to attempt to slap a 92mm in the back, and the grill is stamped for an 80. I may, though, just put an 80 back there and put the other 92mm in front.

Basically, the case is a 7237, and I have 2 92mm fans, and the 80mm that came with it. I was gonna put a 92 in front and back, and either not use the 80, or put it up front, or blowing on the cpu or something.

I haven't gotten the case yet, but I will have it for at least a week before the rest of the parts start showing up, so taking the stuff out isn't really an issue. I'm just trying to decide what to do for when the case gets here.
 

GasX

Lifer
Feb 8, 2001
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In my 7237, I have a 92mm intake on the front and the original 80mm exhausting in the back. Factoring in the power supply fan and the poor ventilation on the front of the case and I probably have major negative pressure in my case. You would make it worse with 2 92 mm fans. Dust is not a big concern where I live, so I am not bothered by the negative pressure. The vent holes on the side of the case allow air to seep in and are somewhat lined up with the CardCooler XT which is blowing on the video card.

This set-up works fine for me and I have a Duron 600 operating at 963 with stock HSF.
 

GasX

Lifer
Feb 8, 2001
29,033
6
81
In my 7237, I have a 92mm intake on the front and the original 80mm exhausting in the back. Factoring in the power supply fan and the poor ventilation on the front of the case and I probably have major negative pressure in my case. You would make it worse with 2 92 mm fans. Dust is not a big concern where I live, so I am not bothered by the negative pressure. The vent holes on the side of the case allow air to seep in and are somewhat lined up with the CardCooler XT which is blowing on the video card.

This set-up works fine for me and I have a Duron 600 operating at 963 with stock HSF.
 

tigereye

Senior member
Oct 27, 2000
327
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Not sure I get the whole negative/positive pressure thing. I've seen it mentioned frequently on here, and never quite caught the gist. Are you saying I shouldn't use 2 92mms at all? Help...
 

GasX

Lifer
Feb 8, 2001
29,033
6
81
In simple terms:

Suppose you had all your fans blowing in. Air would build up in the case and seep out where ever it could. This is positive pressure. In a dusty area, you can use this to your advantage. Put filters on all of your fans and air will only enter the case through the filters. If your case does not have a lot of places for air to seep out, you will have bad ventilation.

Dust aside, the ideal situation is to have equal flow in and out. A secondary rule of thumb is to have fans near the top of the case blow out and near the bottom blow in.

I would go with the 92mm's myself and to hell with the pos/neg pressure.
 

tigereye

Senior member
Oct 27, 2000
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So, if I read correctly, you would put a 92 front and back and not worry about the 80 at all? I don't worry about a lot of dust, either, so sounds like positive pressure isn't a big deal for me.

 

GasX

Lifer
Feb 8, 2001
29,033
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81
If you are motivated, drill yourself a side blowhole lined up with the CPU. You can use the 80mm for that. Otherwise, you have no useful place to put it.
 

conlan

Diamond Member
Jan 27, 2001
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tigereye.... simply put , add up the CFM of your intake fans (lets say 92mm for example) and then add up the CFM of your exhaust fans (again 92mm) 92-92=0 or nuetral pressure. now lets say you have an 80mm exhaust fan 92-80=12CFM positive pressure. switch the 80mm to the intake and the 92mm to the exhaust 80-92=(-)12CFM negative pressure. however this does not take in account any restrictions you may have (especially on the intake side). i agree with mwilding on the nuetral pressure theory , however , with the restrictions on thr front of your case , you would need a higher CFM fan on the intake to achieve this . i use a 120mm on the intake and a 92mm on the exhaust , however i think your 2- 92mm fans should work well also.
 

Supradude

Golden Member
Nov 3, 2000
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since your considering hacking the case anyway, why not leave the 92 up front, 80 in back, and add an exhausting blowhole on the top of the case... this position is great cause it is in the optimal exhausting position, and draws air over your cd-roms to a small extent...
 

tigereye

Senior member
Oct 27, 2000
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Can't do a blowhole, the kids'll stick stuff in there, ;) and the wife wants it to keep as quiet as possible, the blowhole'll add too much noise. The 80mm comes with the case. I'm not really too worried if I get to use it or not. The 2 92mm are papst fans that do 49 cfm each. Then, of course, we have the fan(s) on the power supply, depending on which ps I end up with.