Quote Originally Posted by Vapor View Post
1) When you go in parallel, the flowrate through the pump is the sum of the two subloops.
2) When you go in parallel, roughly the average of the pressure drops of the subloops is the pressure drop across the entire loop (or across the pump, depends how you look at it). This means that at any given pumping power, flow increases.
3) Because restriction is down overall (by a lot), flowrate increases. When flowrate increases to the 2.0 to 3.5GPM range (from the <1.5GPM range), efficiency increases noticeably...so you actually have more pumping power at work.

You throw all three of those into an equilibrium (such is fluid dynamics....the three variables have a lot of dependence and codependence) and you actually end up getting higher flowrates in each subloop than you would in one big loop! Back of the napkin math says roughly 1.5GPM through both loops
Great explanation!

Did you/skinnee compare the res against running two loops in parallel the "normal" way? If I understood you correctly, we're exploiting the shape of the D5's P/Q curve, but it's not clear to me if or how the res increases performance on top of that.

Anyway, great to have more options!