I have a basic 15,000 gallon pool with 1.5" lines. Three return jets tee'd somewhere underground off of one return line from the pump. On the suction side, there is one skimmer and one bottom drain that feeds through the skimmer. No water features or other fancy stuff. The filter is a new StaRite System2 PLM-300.
This pool had a Pentair Pinnacle 1.25 SFHP pump on it. That pump produced a suction of 21 inHg at the bottom of the volute and a filter pressure of 7 psi, for a RDH of 19.17 and a SDH of 23.73. According to the pump curve, this was pumping about 65 gpm -- too fast for the 1.5" lines.
I downsized the pump to a Pentair Superflo 0.95 SFHP. It produces a suction of 14 inHg at the bottom of the volute and a filter pressure of 6 psi, for a RDH of 16.86 and a SDH of 15.82. According to the pump curve, this is pumping about 50 gpm -- still slightly too fast, but this is the smallest pump in the Superflo line.
Why is the suction dynamic head so high? These numbers are *way* higher than the estimates that I would expect based on the formulas in the sticky thread in this section.
I think I understand how most of this works based on the excellent information found here, but I'm obviously missing something.