Positive case pressure questions?

[Throckmorton]

I was thinking about a vacumme gauge for a car, but I dont know if the increments get low enough to check it. You can get vacumme gauges for cars in inches of mercury with vacumme and boost readings, or you can find or make a manometer wich is easier to calibrate than one would think. I dont see why a manometer used with water instead of mercury wouldnt work. I know they use inches of water to flow test cylinder heads. Maybe google "DIY cylinder head flow bench". But I did look at some industrial gauges that could be installed on the case. EXPENSIVE.

All you have to do is take a little piece of tissue paper and hold it in front of a vent hole. If air is coming out you have positive pressure.

 

[EarthwormJim]

Don't have to keep it out. One of the benefits of positive pressure is that dust doesn't settle out like negative pressure. Instead of low velocity laminar intake streams from every opening that stay low velocity until the air is within millimeters of the exhaust fan, you have high velocity intake streams that generate turbulent flow within the case and can exhaust that dust-laden air through every crevice.

If it were that easy, why do fans themselves get dusty?

 

[Socio]

The whole point of positive pressure is the case doesn't have to be airtight. This is really simple. Put filters on your intake fans and don't worry about using any exhaust fans. If you do use exhaust fans you have to make sure the pressure from them doesn't overpower the intake fans (which are weakened by the filters). So it's easier just to not have any exhausts aside from the graphics card and power supply. Air will still flow out of that big hole behind your CPU just fine because you have positive pressure.

People overthink computer case cooling. It's not a damn nuclear reactor.

Sounds like the best approach if using exhaust fans would be to use fan a controllers to balance\tweak the intake and exhaust fans to make sure the exhaust fans to not overpower the intake fans while still providing the optimum heat exhaust.

 

[patinvedis]

In reality positive pressure is difficult to achieve inside your case. If you look at the layout of your typical tower case, the air intake is at the front and hits the HDD cage right away.

At this time your airflow is mostly gone and the air warmed by the HDDs will escape from any possible opening nearby.

I am not saying that positive airflow is impossible to achieve, it greatly depends on the layout of the case, and the system resistance (how much resistance the air meets as it flows inside the case).

As far as dust and filters are concern, you need to bear in mind that filters greatly affect airflow and that they need to be cleaned often. Depending on the environment your computer is, they need to be cleaned as often as every 6 to 8 weeks.

 

[dma0991]

In reality positive pressure is difficult to achieve inside your case. If you look at the layout of your typical tower case, the air intake is at the front and hits the HDD cage right away.

At this time your airflow is mostly gone and the air warmed by the HDDs will escape from any possible opening nearby.

I am not saying that positive airflow is impossible to achieve, it greatly depends on the layout of the case, and the system resistance (how much resistance the air meets as it flows inside the case).

As far as dust and filters are concern, you need to bear in mind that filters greatly affect airflow and that they need to be cleaned often. Depending on the environment your computer is, they need to be cleaned as often as every 6 to 8 weeks.

Pressure isn't nullified by the case layout. Internal pressure isn't governed by the airflow or directed airflow. That is why you can have fans which does a great amount of airflow but doesn't do much for static pressure, vice versa.

All positive/negative pressure does is create a pressure difference. You can expect to push so much air in without expecting it to exit somewhere or pull out air without expecting it to enter somewhere. There was this room I was at with 2 industrial exhaust fans and a hole on the wall. The small volume of the sealed room creates a negative pressure difference and a pillar of air goes through the hole and into the room. The same pressure difference concept applies to cases, positive or negative.

Regardless of the downside of filters, its a crucial part to make it all work and reduce dust at the intakes.

 

[patinvedis]

Pressure isn't nullified by the case layout. Internal pressure isn't governed by the airflow or directed airflow. That is why you can have fans which does a great amount of airflow but doesn't do much for static pressure, vice versa.

All positive/negative pressure does is create a pressure difference. You can expect to push so much air in without expecting it to exit somewhere or pull out air without expecting it to enter somewhere. There was this room I was at with 2 industrial exhaust fans and a hole on the wall. The small volume of the sealed room creates a negative pressure difference and a pillar of air goes through the hole and into the room. The same pressure difference concept applies to cases, positive or negative.

Regardless of the downside of filters, its a crucial part to make it all work and reduce dust at the intakes.

Positive air pressure means that there is more air entering the case than being exhausted. Without airflow this is not possible to maintain. You cannot create positive or negative pressure without fans.

In any case if preventing dust from entering the case is you main concern, by all means use higher flow intake fans than exhaust fans and use filters.

 

[dma0991]

Positive air pressure means that there is more air entering the case than being exhausted. Without airflow this is not possible to maintain. You cannot create positive or negative pressure without fans.

In any case if preventing dust from entering the case is you main concern, by all means use higher flow intake fans than exhaust fans and use filters.

When have I said about no fans? You've said that whatever air goes into the case gets cancelled out the minute it hits an obstacle like a HDD cage. That made no sense at all.

High airflow fans is becomes less effective if you're adding in a filter. Using a static pressure optimized fan will perform much better under such restrictions.

 

[patinvedis]

When have I said about no fans? You've said that whatever air goes into the case gets cancelled out the minute it hits an obstacle like a HDD cage. That made no sense at all.

High airflow fans is becomes less effective if you're adding in a filter. Using a static pressure optimized fan will perform much better under such restrictions.

You said that positive pressure had no relation to airflow. It looks like we don't understand each other, but no worries . No, air doesn't not get "cancelled out". And I agree that you would need fan with higher static pressure to circumvent obstacles.

 

[maxcellerate]

I'm putting together a new build and going for a 'positive pressure' case, sealing everything but the filtered intake fans, of which there are many but mostly big, low static pressure big fans, with the idea of blowing everything out the top vent (top back exhaust is used for gpu vent & psu is bottom mounted so doesn't count). The top vent has an Corsair h100i rad which I'm trying (as I type) to get lined up with the holes in a Thermaltake level 10 GTS case. They won't by the way. No matter which way I try. In fact if someone had deliberately designed two components to NEVER fit each other, they couldn't have done better than the above combination... if that's the right word, and I don't think it is.
Anyway, to get maximum cpu cooling I'm using 4 high(ish) static pressure exhaust fans on the h100i (2 internal 2 external), and sealing what holes I can. Yes, even the PCI slots!!!
I hate dust, almost as much as I hate the idea of having to think about cleaning out a computer case every '6-8 weeks' (yeh, like that's going to happen). The last time I re-jigged the inside of a box it was very difficult to tell where the carpet ended and the computer began.
Does anyone think this is enough to keep out dust or should I reverse the flow of the h100i rad, that would after pull colder external air in over the rad- but then into the case.
Tricksey innit?