Whenever people talk about loops and required pumping power there's always a lot of assumed information that gets trickled through forums such as "that XSPC 750 doesn't have much power" or " you'll need a second pump for that loop" that are never backed up with any hard facts.
I recently had the opportunity to play around with 2 of Koolance's PMP-450S. According to martin's liquid lab, these are the most powerful pumps out there.
So I decided to try and find out just how much pumping power did I need. The answers may surprise you:
Low restriction loop
Test HW- i7-990x @ 4.43GHz 1.41Vcore, 1.35VQPI, loaded with stresscpu2 on redhat 64
I tested 2 blocks as well as with 1 or 2 radiators, and 1 or 2 pumps at 12 and 24V:
High Restriction Loop
Test HW - i7-920 @ 4.2GHz with XSPC raystorm cpu block, Rampage III Extreme with EK full cover block, 3xGTX480 with Koolance full cover blocks in parallel. Loaded with folding at home (SMP-6 on CPU + 3 advmethod WUs on GPUs)
Here you can see that the extra pumping power did not affect the GPUs at all. Possibly because they were in parallel and required sinificantly higher flow rates to benefit. Going from 12V to 18V did help the CPU temps, but by a tiny amount. Any increase in flow from 18V to 24V again was offset by the extra pump heat dump into the water.
What does this mean to you
With unlimited money:
- 1 very unrestrictive CPU block and 1 very unrestrictive radiator = 1 normal pump
- 1 "normal" cpu block and 1+ "normal" radiators = 2 normal pumps or 1 strong pump
- 1 "normal" cpu block + GPUs in parallel = 2 normal pumps or 1 strong pump
- 1 "normal" cpu block + GPUs + motherboard = 2 strong pump
In reality though the cost of 2 strong pumps isn't really justified given the performance benefit. Possibly with many radiators and 2 loops each with 1 strong pump, there may be justification.
- Weak pumps (not recommended) would be something like the XSPC 750 or below
- Normal pumps would be something like a D5 vario, DDC 2, aquastream XT
- Strong pumps would be something like PMP-450S, DDC 3.25, PMP-400 etc
For 90% of watercoolers the best choice is almost always 2 "normal" pumps in series or one "strong" pump. However if you are purposefully designing an ultra low or high restriction loop, you may prefer less or more pumping power.