This question has to do with sending liquid coolant at a temperature of -25C thru standards computer water cooling components, like a CPU Waterblock, GPU Waterblock, and 120MM Liquid Radiator.

I would like to know what would happen to the flow rate and pressure if the situation is as follows.

  1. A single powerful high flow / high pressure pump is supplying the liquid coolant.
  2. Right before it reaches the components to be cooled, the coolant is split in to separate streams, so that all components get a dedicated stream, and operate in parallel in stead of inline.
  3. Right after the components, the streams all combine back in to one, and are sent back to the liquid reservoir.

The concern I have is that I might have very big flow rate differences, between the different components in the system, because some components are more restrictive then others. For example the CPU water block is a lot more restrictive then the 120MM Liquid Radiator.

Can you guys predict how the liquid will act?

Would I be able to add a simple open close valve at the end of each component, and adjust the flow rates so they are more or less closer to each other?

Am I completely wrong, and will the system self balance some how?

Sidenote: If you are wondering why am doing this, its because, this water cooled computer is housed inside an air tight box, that also contains the liquid radiator to cool the air inside. This prevents condensation to form on the electrical components, and allows you to liquid cool the computer hardware, using standard water cooling components to very extreme sub zero temperatures with out the risk of condensation, for the purpose of extreme overclocking.

  • $\begingroup$ By "sub-zero" temperatures you mean C or F? Also, you may want to look at Bernoulli's principle. $\endgroup$
    – Kyle Kanos
    Feb 7, 2015 at 23:23
  • $\begingroup$ I mean C - Celsius, Thank you, I will read up on Bernoulli's principle! $\endgroup$
    – Max
    Feb 7, 2015 at 23:34

1 Answer 1


You can analyze this problem in a similar manner as in analyzing an electrical circuit of parallel resistors connected to a voltage source (your pump pressure) and ground (your reservoir). For continuity, the pump inlet flow is equal to the reservoir outlet flow. If all the resistors are the same value, they will all have the same flow and the sum of their flow will also be equal to the pump inlet flow. Lower resistances will flow at higher rate, and higher resistances will lead to lower flow rate, but the sum of the flows will always add up to the inlet pump flow.

If you are unable to engineer precise pipe diameters and equal distribution, some of the split pipes may flow more or less and thus lead to colder or hotter points on your CPU(s). So yes it is possible to 'trim' the flow rates to compensate by using small gate or needle valves, but that gets more complicated and expensive. So it's best to start with good precision in your design.

The pipe resistance is more sensitive to diameter than length.

Bends in the pipe will increase resistance so you'll want to have the same bend angle/radius at all your split joints if that is possible.


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