We bought a house in Plymouth, MA 5 years ago with an older IG vinyl pool, 25K gal. It came with a 2 HP Hayward Superpump (discontinued model), 36 sq ft Nautilus DE filter and we have a Tiger Shark cleaning robot. Pipes are 1.5 inches. 2 skimmers and 4 returns. There are no waterfalls, heaters, spas or any type of special features. Within 24 hours of opening the pool this Spring, the pump died. I realize it might be possible to just replace the motor but we're looking at a new pump to try to improve efficiency. All the research we've done indicates that when we look at the pool pump curves, we want about 50 gpm flow and head is about 45 (although I realize it is dynamic).
If you look at the performance curves on the Pentair Superflow VS pump (which we are considering), then we'd be looking at running the pump at Step 1 speed or 3100 which isn't that much better than the 3450 we've been running it at (not much electricity savings). (Brochure with performance curves http://www.pentairpool.com/pdfs/superflovsDS.pdf)
My question is that the argument for a VS pump seems to be that you can lower your rpms, increase your water turnover time (run pump longer), but still save money and maybe even improve filtration. Except, if in my system, the head is 45 (and head as I understand it is resistance in the system), then wouldn't running the pump at lower speeds effectively stop circulation since there wouldn't be enough flow to overcome the inherent resistance?
I think I may be misunderstanding something fundamental but cannot for the life of me figure out what it is.