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Negative-pressure Watercooling?

L

Little Grabbi

Gawd
Joined
Aug 15, 2003
Messages
565
So here's tha plan. I hook up a normal, run-of-teh-mill watercooling setup, but with a valve on top of the res. The res would be a bay res, 2 bays high, and about half full. An air pump would be attached to this valve, which shuts off at -5 PSI.

The idea is to eliminate leaks by negative pressure, so only air can get in, but water can't leave. Think I should do it?
 
Wouldn't that result in a bit too much pressure and spring leaks? :eek:

I think I saw something like this mentioned in a recent thread (it was the watercooling horror stories thread or something like that)..
 
There's absolutely no point to this setup.

If you properly setup a normal system and leak check it, you won't have a problem.


But hey, if you want to waste the money, have fun.
 
Why even worry about leaks?

You can get deionized water at a local car shop (used for tapping off batteries), or if you have connections to the pharmaceutical research industry, look for DEPC or HPLC water which has an ion level so low you can't drink it. Needless to say, it does not conduct electricity.

It's currently going at like $40.00 for 4 L or $18 for 1 L, which should be enough to last you awhile. Also, because it lacks ions in any appreciable quantity, it won't corode the metal in your water block, and bacteria/algae shouldn't grow in it.

If anyone needs any information, feel free to ask.
 
I have access to deionized water. I work at a lab.

But deionized water is lame, it involved no effort. My setup would. And I wouldn't use water anyway, I'd use something with a higher specific capacity.
 
Here is why this idea falls short of practicality.

1)If you have negative pressure AND there is a leak, than the air will enter the system and equalize the pressure. Keep in mind that the pressure differential will actually aggravate this process.

2)Once the pressure is equalized, you will then have a leak.

3)If you dont have a leak and also have negative pressure, you will be putting more strain on your components with no benefits.
 
haveing it a neg pressure is going to cause it to kink.
=No waterflow.
=Overheated CPU.

Luck........:D
 
Talk about hard on parts.... I would suggest Distilled water, not Deionized water.
 
Originally posted by Mysogonist
Here is why this idea falls short of practicality.

1)If you have negative pressure AND there is a leak, than the air will enter the system and equalize the pressure. Keep in mind that the pressure differential will actually aggravate this process.

2)Once the pressure is equalized, you will then have a leak.

3)If you dont have a leak and also have negative pressure, you will be putting more strain on your components with no benefits.
Click to expand...

1) yes

2) I meant that the air pump would keep the pressure slightly negative.

3) what strain? I aint talking ybout .75 atmospheres difference. Just a few PSI
 
Leaks usually occur because of pressure difference between the pump and something restrictive, like a waterblock. Sucking a little air out of the res is not going to change the fact the the block still restricts water flow and creates a pressure drop. What you would need to do is increase the ambient pressure to whatever your highest water pressure is in the loop.
 
How about this.

Cranck the sucker up to ~4500 PSI, record a video, then host it up, I'm pretty sure that everyone here would like to seee your tubing fly everywhere =D.

No seriously now, I don't think it would do anything, as there are really no problems with air bubbles that I've heard of as long as you leak test it for a while.
 
I don't know of any kind of tubing that won't collapse under 7 inches of mercury, either.

Matt.
 
Originally posted by Little Grabbi
1) yes

2) I meant that the air pump would keep the pressure slightly negative.

3) what strain? I aint talking ybout .75 atmospheres difference. Just a few PSI
Click to expand...

A 5 PSI drop (since 1 ATM is about 14.7 PSI) leaves you at about .66 ATM.

5 PSI is a huge strain for small piddly shit like WC setups. Your car radiator will failover at 16 PSI. (that's a 1.3 PSI difference)

PV=NRT doesn't quite hold true for water if memory serves, either, so the volume of the water won't change, just the air, and something has to give.. The only thing it will do is accelerate leak formation and then cause a catastrophic mechanical failure around it.

Depending on the temperature, you'll also drop the pressure below the vapor pressure and boil off the water.

Do I need to keep going?
 
Originally posted by enraged78
I don't know of any kind of tubing that won't collapse under 7 inches of mercury, either.

Matt.
Click to expand...

Did I miss something in this thread or was this reply meant for another thread? I'm Confused on what you are talking about
 
Originally posted by enraged78
I don't know of any kind of tubing that won't collapse under 7 inches of mercury, either.

Matt.
Click to expand...

It's still at 19 in Hg if he does the 5 PSI drop, so it might withstand it, but not even Tygon Pressure tubing is rated for over 10 psi. It's just a poorly thought out idea.
 
Originally posted by mwarps
It's still at 19 in Hg if he does the 5 PSI drop, so it might withstand it, but not even Tygon Pressure tubing is rated for over 10 psi. It's just a poorly thought out idea.
Click to expand...

That's also 10psi inside the tube before it bursts, it would probably take alot less than that to collapse it.
 
Originally posted by zer0signal667
That's also 10psi inside the tube before it bursts, it would probably take alot less than that to collapse it.
Click to expand...

Actually, it's pressure rated to 35 inside. The vacuum rating is just that.

Either way.
Collapsing tubing - bad.
Standard pressure - good.
 
Originally posted by DocFaustus
Did I miss something in this thread or was this reply meant for another thread? I'm Confused on what you are talking about
Click to expand...

Nope, I just screwed up my negative pounds per square inch to inches of mercury calculation. Inches of mercury is one method of how vacuum pressure is measured. If one atmosphere is equal to 14.696 PSI, and one atmosphere is also equal to 29.530 inches of mercury, then you can calculate that this kid is trying to keep his water cooling lines at -10.0469 inches of mercury. Most lines would collapse at this pressure, or lack thereof. Sorry, I should have been more descriptive.

Matt.
 
Originally posted by enraged78
Nope, I just screwed up my negative pounds per square inch to inches of mercury calculation. Inches of mercury is one method of how vacuum pressure is measured. If one atmosphere is equal to 14.696 PSI, and one atmosphere is also equal to 29.530 inches of mercury, then you can calculate that this kid is trying to keep his water cooling lines at -10.0469 inches of mercury. Most lines would collapse at this pressure, or lack thereof. Sorry, I should have been more descriptive.

Matt.
Click to expand...

There is technically no such thing as negative pressure, just a lack of pressure. At 0 in. Hg, there are 0 particles in the volume under investigation.

He is attempting to hold his lines at 19 in Hg. (assuming a 5 psi differential)
 
Originally posted by mwarps
There is technically no such thing as negative pressure, just a lack of pressure. At 0 in. Hg, there are 0 particles in the volume under investigation.

He is attempting to hold his lines at 19 in Hg. (assuming a 5 psi differential)
Click to expand...

That's cool, but how did you get 19 in Hg? All the formulas I have suggest a 14.696 to 29.530 ratio of PSI to in Hg. In taking my experience from automotive turbocharging, the polar opposite of five pounds of boost is 10 in Hg. Is this right?

Matt.
 
even if the air gap at the top of the res was at negative pressure, you'd still have positive water pressure in your tubing if you're pumping the water
 
Intresting. This is pretty complicated as there are lots of things to take into account. First off, for this to work you would have to have a certain volume of airspace to keep the air pump from sucking water. This could be considered a con as reducing overall system capacity hursts performance. How much would depend on overall system capacity and % of water capacity traded for air volume.
Next, If you have a properly built system, leaks should not be an issue. If a leak were to occur, you would be introducing air bubbles into the system from the point of leakage. These air bubbles would be circulated through the loop until they reached the air pocket from where the vac pump is drawing. Who knows how long air bubbles would stay trapped in the water flow before being released into the air pocket or they may just form another air pocket in your radiator or something. Again, air bubbles in the water is a con.
The lower pressure air pocket would not effect overall water flow as the reduced pressure would be effecting (in principal) both the inlet and outlet sides of the loop, however, given enough vacume, the tubes may collapse or narrow which WOULD restrict flow in a big way. Again, another potential con.
Yet another concern would be air pockets forming in places other than where the air pump is drawing from. This would cause the water to be displaced and the only place it could go would be into the air pocket where the vac pump is drawing from. The vac pump would sinply draw more air out to compensate and if enough air pocketed in the system, the air pump would eventually suck water. Again, a potential con.
The only pro I could see with this, is if air is sucked into the system instead of water leaking out which like I said, can cause a number of other problems. IMO, any benefits of this would not really be worth it. Yes it could be a failsafe, but an infinate better failsafe is to build the system properly so leaks do not occur.
 
Originally posted by Little Grabbi
I have access to deionized water. I work at a lab.

But deionized water is lame, it involved no effort. My setup would. And I wouldn't use water anyway, I'd use something with a higher specific capacity.
Click to expand...

Specific capacity? And you work at a lab?:rolleyes: It's specific heat, and at standard conditions (30 Degrees Celcius, 1 ATM), water has the highest specific heat of any liquid.
 
Originally posted by enraged78
That's cool, but how did you get 19 in Hg? All the formulas I have suggest a 14.696 to 29.530 ratio of PSI to in Hg. In taking my experience from automotive turbocharging, the polar opposite of five pounds of boost is 10 in Hg. Is this right?

Matt.
Click to expand...

14.7 psi is 29.9 in Hg is 760 Torr is 1 ATM... etc.

Take away five psi from standard pressure, you've got 9.7 psi or .66 ATM, multiply .66 by 29.9 in Hg, you get about 19 in Hg.

Five pounds of boost (whatever that means) would be 10 inches of Hg, yes.. but it's subtracted from 29.9.
 
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