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Working pressure?

post #1 of 11
Thread Starter 
I've just gone through several water cooling tutorials, and none seem to touch on the working pressure of a typical system. It may just be an oversight on my part. I've used the Iwaki RD-30 as an example, and it supposedly produces 10.6psi at 3.5gpm(Martin's). I understand that there will be pressure loss as the water passes through the system components, and I'm also aware of the negative correlation between system pressure and flow rate. But is 10.6psi a typical pressure for a water cooling system?

Thanks,

James
Edited by jrich7720 - 11/14/13 at 6:33pm
post #2 of 11
Pressure in a closed system depends entirely on where you're measuring it, and what you're comparing it to. at the pump inlet, you'd see "negative" pressure.
 
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post #3 of 11
You shouldn't have or want "pressure" so I'm not sure why you're even asking this. If pressure is building up, it means you have too much restriction through your components.

If you're trying to compare this to the pressure in an automotive cooling system; that pressure is from the expansion of the water due to heat and the system is designed to contain some of that pressure because it increases the coolant's boiling point. Automotive coolant is exposed to temperatures well above boiling point. None of your components should be getting that hot.

Pressure of your system is a moot point.
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post #4 of 11
Taking what I said earlier about references, and building on what he said about cars - there are two ways to measure pressure in a car system -
1: the most common is system pressure vs atmosphere - that's what we're talking about when it comes to boiling points and whatnot.
2: pressure differential inside the system itself - you can't have flow without pressure differential, and a well designed cooling system doesn't require a large pressure differential.
 
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post #5 of 11
Did you read Martin's Pump Planning Guide? It gives examples of pressure drop with sample components as examples.
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post #6 of 11
Without pressure, the fluid doesn't move. Every fluid system has what is called a "system head curve" ..... It starts at 0,0 as at no flow, there's no pressure.....as flow increases, the fluid moving past restrictions causes back pressure. This resistance increase at a rate at a geometric rate with the pressure increase being approximately proportional to the increase in flow to the 1.85 power.....(google Hazel Williams equation if the urge strikes ya for more info)..... so double the flow and ya increase backpressure by 3.6

So this curve starts out prtty flat but quickly rises in slope based upon the ratio above. The pump curve starts at what is called the "shut off head' ....this is at the 0 flow point and is the point at which the pressure is high enough that the pump can not move any water against it. And unlike the system curve which goes up and it moves to the right, the pump curve drops as it moves to the right. At some point the curves intersect and that is your operating point. Martin gives a good example here:



Each restriction, each fitting, each change in direction, even each air bubble, adds backpressure or "head loss".....the pump will pump as much as it can until the pressure it can provide is an exact match to the head loss in the system.
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post #7 of 11
It's a pressure differential that is causing the fluid to move. There is a corresponding vacuum behind the impeller.

The system as a whole should have very little static pressure in it. Maybe a couple PSI but that's it. With the coolant running well below boiling point, there is no need to have pressure in the system. I don't know any other way to make this more clear.
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post #8 of 11
Quote:
Originally Posted by jrich7720 View Post

I've just gone through several water cooling tutorials, and none seem to touch on the working pressure of a typical system.
I don't know why you would need to concern yourself with something like that.
post #9 of 11
Quote:
Originally Posted by Cavi Mike View Post

It's a pressure differential that is causing the fluid to move. There is a corresponding vacuum behind the impeller.

The system as a whole should have very little static pressure in it. Maybe a couple PSI but that's it. With the coolant running well below boiling point, there is no need to have pressure in the system. I don't know any other way to make this more clear.

Attend my fluids course, we'll talk about it. smile.gif
Edited by JackNaylorPE - 11/16/13 at 2:10pm
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post #10 of 11
Thread Starter 
Quote:
Originally Posted by Fulvin View Post

I don't know why you would need to concern yourself with something like that.

I am doing research concerning the use of borosilicate glass tubing(that is typically used in scientific and industrial applications) in a PC water cooling system. I just wanted to compare the pressure of a typical system to the pressure rating of the tubing. A lot of the tubing is rated up to 100psi at 35C, at least the heavy wall stuff. It should be fine. The problem now is finding a way to adapt the tubing to G1/4.
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