Expensive but not reliable helical rotor pumps.
I operate three solar pump wells off grid for 13.5 years and use a generator to makeup for overcast days and high watering demand. I have had great results with early versions of the 11SQF-2 and 6 SQF-3 pumps (8.5 yrs MTBF) made in denmark. Two recent wells were drilled and I of course went and purchased two 11SQF-2's, both were made in mexico. The two solar pumps stopped pumping about 3 months apart. And just a couple of months out of a "2 year warrantee period". I asked a local grundfos rep to look at my pump but there response was "it was out of warrantee". So I proceeded to find out the cause of failure. I removed the rotor jacket and tried turning the rotor by hand but stops against a hard metallic object. So I know it was not worn out. My guess without cutting open the motor ....is that one of the magnets came loose inside the motor housing. My concern is that both pumps failed early without warning. Both may have quality issues. This discussion may open up a big can of worms but id like to hear what others are experiencing.