Originally Posted by abdullanur
could i just create a loop with an iwaki rd-30..it provides the most pressure right?but d5's provide more flow..:/...i am a total noob in the terms of pumps..:?
do i need more flow or more pressure?
The Iwaki RD-30 has just slightly higher pressure than a dual MCP35X, but insanely more flow at the same pressure levels.
The MCP35X provides both higher pressure and higher flow than the D5, but it favors pressure over flow (it gets really hot when the flow rate gets high); so if you had a lower restriction loop, the D5 would be a better fit for higher flow. In your case, though, you have tons of blocks, so your restriction will be high: hence why I recommended the dual MCP35X over the D5s.
Even with a bunch of blocks like this, you are still not in Iwaki territory, it would be overkill; you'd want to think about the Iwaki if you're planning to run two or three high restriction loops in parallel: the Iwaki shines at providing ridiculous flow rates at pretty constantly high pressures.
If you plan to run the loop with most everything in series, a dual D5 just wouldn't have the pressure to push through fast enough having that many blocks. Your question is kind of strange though because pressure and flow are very much related. At 1.5gpm, a dual MCP35X has about 11.5psi pressure; at the same flow rate, a dual D5 has about 8 psi (more than 30% less).
The water blocks you choose to use will have a dramatic impact on your restriction as well, since you have so many blocks; but you haven't stated which blocks you are using so i can't run any numbers. If we assume you're using the least restrictive blocks possible, though, then a dual D5 on 100% would put you just at or under 1.5 gpm without considering any restriction but the blocks: tubing, fittings, G1/4 connections, etc. If we assume you're using the most restrictive, then you'd be somewhere around 0.1-0.2gpm with the blocks only. Most likely, you'll fall between so if you want to get 1+gpm, I'd recommend the extra pressure you get from the dual MCP35X. If you have low restriction blocks, then you could always turn the MCP35X down a bit.
The second diagram I made was just to show how you could still use D5s if you wanted by splitting up the restriction between two sets. I agree with theseekerfun saying that 4 D5s would be a lot of money though, which is why I suggested dual MCP35X first.