I am trying to repair my aquarium pump. It is an axial-flow (rotary) propeller pump. It accidentally drew air when I was refilling the aquarium after moving it.

After that it didn't pump anymore, but made an unhealthy noise.

As I had to work with (MUCH MUCH) bigger rotary pumps some time ago, I know that those pumps have a bearing that is lubricated using the water flowing through the pump (and not by some lube). When big pumps draw air, the heat melts the bearing. Fortunately, this didn't happen with my (small) pump.

I know that because I opened it.

Looking at the drawing, how is it possible that the magnetic cylinder, to which the propeller is attached, can rotate around its own axis (resulting in the propeller turning) and its tilt direction (resulting in a circular movement of the propellers center)

Do you have any idea how this is used to pump the water (I know how a rotary pump works, but am unsure here because of the complete open top. Is a circular movement of the propellers center necessary?) ?

And: What do you expect to be in the surrounding "black box"? I guess there must be some sort of electromagnet.

BUT: Even when the pump is turned off, there is some magnetic force on the cylinder (resistance against pulling it outside of the surounding box).

Any hints on this?

I am trying to understand how the pump is working, to then be able to locate the problem and fix it.