jmayerl,
I did a similar project last year having been given a 4x40 8 post unit that came out of a dialysis center. I pretty much tore it down and rebuilt using the parts and completely eliminating the electronics in favor of a VFD with a control circuit and my own pressure switches. I ended up using 3 posts- two in parallel feeding one in series. I got the pyramid idea from the guys at MES. We are using their 120gph membranes. When I got the unit it came with a 5hp, 3phase, 35 stage pump. I quickly abandoned that... The pile also included a 2hp 5 stage Grundfos that I coupled to a phase converting VFD also from MES. I was never able to achieve pressures higher than 150psi at 120 gph. I have been told by a commercial plumbing contractor that those pumps do not like viscosity and has suggested a positive displacement pump. This year I'll be looking at procons- probably 240-265gph and without the relief valve. I'm hoping to run 200-225psi. I anticipate i should get around 200gph at that pressure and theoretically get 8% in one pass. Just not sure yet how much motor I'll need for that. I will get a 3phase and use the VFD as a throttle to find the sweet spot - so to speak. If i can't get 8% I'll add a recirc loop which will slow my output, but I'm going to add a low pressure switch to the feed pump so I can turn it on in the morning and come home from work and boil concentrate. That's the plan...actual results may vary lol