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Tubing diameter vs pump pressure

post #1 of 2
9/8/12 at 9:50pm
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I'm still planning my WC loop (if I can ever get around to it), and a thought crossed my mind. I know that when you increase the flow channel, you get a pressure drop (i.e. putting your thumb on the end of a garden hose to build pressure, then removing it). My question is, is there a point when you HAVE to buy a stronger pump? Example, you buy the Rasa RS240 kit, which comes with 7/16" ID/5/8" OD tubing. If you moved to a tubing with, say, 1/2" ID, would you need a pump better than what comes with it? I know there are other factors (components, etc), so for the sake of it let's assume the loop is pump/res->2x120 rad->CPU->GPU->1x200 rad->res/pump. The pump in the kit appears adequate for this loop, but would there be a point that increasing the ID of the tubing would require a stronger pump?
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post #2 of 2
9/8/12 at 10:14pm
Yes, but not by tubing size. Your pump needs depend on the restriction of your loop. You don't want the total series psi drop in your loop to exceed your pump's maximum pressure at around 1gpm. Water will still move if it does, but it will move slowly and cause significant negative pressure in the tubing before the pump intake.

It's completely dependent on the individual components. There are some radiators with higher restriction than even most water blocks; there are some water blocks that have almost 10 times more restriction than others. If the components you want have been tested, then you can use the PQ data from various sites to figure out if your pump is enough. The two most often referenced are Skinnee Labs and Martin's Liquid Labs.

http://martinsliquidlab.org/
http://skinneelabs.com/

Martin also created a spreadsheet with some data to get a rough estimate of flow rates and pressures given certain parts.
http://martinsliquidlab.org/pump-and-radiator-optimizer-spreadsheet/


You don't need to worry about tube diameter unless you get too small. Pretty much all components work with the standardized G1/4" threads, so the trip getting there doesn't affect pressure much. You'll see a little less pressure drop with larger tubing due to the water flowing slower, causing less friction, etc.
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