Getting positive case pressure

[BangDroid]

I'm trying to get positive case pressure in my bequiet Pure Base 600 case. Mainly because my front IO is getting too much dust, I also recently added an optical drive and don't want that to also become dusted. I have added 2 additional 140mm fans, one at top and another front. Case comes factory equipped with front 140mm and rear 120mm. 

I remounted fans B) and C) inside the case, as opposed to the standard position, to increase the distance from the front panel because I found they were being choked somewhat. I did a smoke test and this has increased their airflow through the front panel.

The fan configuration is; B) C) D) are controlled by case fan switch (usually on medium unless it's hot and high usage)

A) is motherboard header DC mode with quiet/low speed fan curve.

 

The Foam things highlighted are dark grey foam panels to redirect airflow to exhaust fans. The case has an adjustable top panel that I leave open on the first height, about 5mm.

 

I would have thought the fan config would produce positive pressure, considering fan A) runs at such a low speed and B) C) and D) are identical and run at same speed.

 

Does anyone have any ideas for what I could change to net positive pressure? Bear in mind that the point of this build is low noise.

 

Also, ignore the ddr2 sticks and floppy disk, they're just for lols

[samcool55]

Keep A and D at the lowest speed possible.

The GPU will also push some air outside (not a lot, but in a scenario where there isn't much airflow it makes a difference) and even if you get rid of fan A, there will still be exhaust because the CPU cooler is pushing air into that direction.

[Fasauceome]

Positive pressure changes nothing about dust build up if you're drawing air over the same place.

[BangDroid]

2 hours ago, fasauceome said:

Positive pressure changes nothing about dust build up if you're drawing air over the same place.

Front IO: USB ports, switches and 3.5mm ports are getting built up frequently. I'd have to think this is due to neg pressure; unfiltered air being drawn into the case through these. Yes, positive pressure would still have airflow through these, but I'm certain the dust would be less.

[BangDroid]

2 hours ago, samcool55 said:

Keep A and D at the lowest speed possible.

The GPU will also push some air outside (not a lot, but in a scenario where there isn't much airflow it makes a difference) and even if you get rid of fan A, there will still be exhaust because the CPU cooler is pushing air into that direction.

I'll try with D) controlled by motherboard on low, and keep B) C) case and see how it goes. Maybe try without A) too.
It's mainly all due to the restricted front airflow of the case I know, but it's what I have for now. 

[LogicalDrm]

On 12/4/2018 at 4:10 AM, BangDroid said:

Front IO: USB ports, switches and 3.5mm ports are getting built up frequently. I'd have to think this is due to neg pressure; unfiltered air being drawn into the case through these. Yes, positive pressure would still have airflow through these, but I'm certain the dust would be less.

.... because fans draw air over them. Positive pressure only has effects inside the case, not outside it. You would need to have reverse airflow (rear, top in; front, bottom out) for changing place/filter where dust accumulates.