Quote:
Originally posted by Blackeagle
A pump that can give a real 3gpm would have a much higher rate at 0 head. So I'm unsure what pump would be needed to drive a 3gpm set up.
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Not necessarily. There are a number of factors involved here, so I'll try to sort some out:
#1: you should really try to get a pump that's going to be energy efficient. What that means is that, to put it simply, take the pump's curve, draw a straight line between max flow and max head, and find the point on the curve that's furthest away from the straight line: that's your "point of efficiency".
#2: some pumps have a curve that is "long", like Eheims, where you get more flow with a relatively small max head. The Iwaki #70 has a tall curve, and you really have to visit that site to see the chart: it's a good read. tip, there's also an Australian site for Iwaki that has some additional info.
#3: you really need to know what your components can do, at different flow rates. We recently brought up the point (again?) that some heatercores peak in efficiency at 1.5 gpm, so if you go with two of those in parallel, you'll be able to minimize the total pressure drop.
#4: pump heat becomes a significant factor. You would do well by being able to calculate the induced heat. Note that the pump heat appears at the flow restrictions, and not within the pump.
Personally, I lucked out with my Little Giant 2-MDQ-SC, which I found for $40, but it'll need special venting. Whatever you spend, it's already beyond cost efficient: nothing can be cheaper than a good HSF, and a watercooling rig will always exceed that. All you can do is minimize all costs. You might want to look into multiple pumps in series, if you understand the limitations.
I think that in your case, you would do better by choosing it backwards: be aware of what your waterblock can do at different flow rates, and what your core will drop in pressure, then see which pump is cheapest, while achieving a reasonable temp.