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Originally Posted by Arivaldo
Butcher,
Our aquarium magnetic pumps (not iwaki) use ceramic/magnetic rotors and DO NOT use any artifice to get direction. Their impeller blades have to be "semi-crazy" (please, just remove a impeller and see) to get start without load. By absence of direction inductor their rotor can spin at any direction (if you rotate impeller with finger it will assume any direction that you want).
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I'm aware they are straight bladed impellors and will move either way by pushing with a finger. But that still doesn't prove they can spin in either direction - after all a fan can be spun either direction by hand if it's powered off, but will only spin one way when powered on.
I haven't cut open an AC pump to check the internals, but I would assume they have some means of setting direction, be it shaded pole or otherwise. If they didn't have one the motor would not spin up at all (the whole point of the shaded pole etc. is that if you don't start the field rotating the rotor will not spin at all). Given the rotor design I'd guess they use shaded pole synchronous motors.