It's not running on a hole, it's running on a cushion of fluid. Done correctly, the inner and outer "hard" pieces should not touch except when stopped (or stopping/starting).
Most automotive engines use this for crankshaft bearings. Two stroke engines (the ones using the crankcase as a "pump") cannot do this and have to make do with ball or roller bearings, which have a lower lifespan than the "hole" ones. Fluid bearings are good.
If you have something, like a rotor or a crankshaft, spinning on a fluid bearing, you then have to deal with the fact that it will not want to stay "centered" on that bearing but will push to one side or the other. With a centrifugal pump rotor, this push (side load) should be fairly small (there will be thrust (pull) from the water coming in the center inlet, but you should be able to counteract at least a good portion of that by angling the rotors and maybe the output chute. I would guess however that the balance won't be perfect because of variables you can't control for - so you need something to keep the rotor from walking off-center. IMHO, that's where sapphire/ceramic gets interesting.
Of course, I'm no pump engineer - and my automotive know-how is laughably out of date.
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