Filter for aquariums

A filter for aquariums containing a filter cartridge and an adjoining head is proposed, which contains in its casing a self-starting synchronous motor with a permanent-magnet rotor and a pump impeller which sits directly on the rotor shaft in a pump chamber whose radial outlet, located on a perimeter side, is situated at the bottom end of the head and opens into a discharge duct leading to the top end of the head. The rotor shaft is provided with a continuous bearing bore and is supported, on a divided shaft formed by two shaft pins, in a precisely fitting manner, but with free running clearance. Each shaft pin is seated, at its end, in an elastic rubber socket. The rotor shaft consists of a carbon material, the shaft pins of a ceramic material. Both parts are expediently run in together and ensure good centring and a substantially true-running bearing arrangement. The pump impeller having rigid radial vanes is clipped onto the rotor shaft axially in a detachable manner. Relative to the rotor shaft, it is freely rotatable by a substantial circumferential angle and has radial damping end stops, against which a fixed radial end stop of the rotor shaft strikes for the purpose of rotational locking (slaving) in the drive direction. The bush, which accommodates the entire rotor and adjoins the pump chamber axially, is open at both ends to form a lubricating and cooling duct which runs between the bush and the rotor and is connected, near the head, to a pressure relief port via a small radial duct. Between the bottom plate and the pump chamber there is a control disc, which can be rotationally adjusted manually, for controlling the throughput. Said control disc has an axially continuous control window with a radial duct adjoining it which is covered axially by the bottom plate and towards the centre communicates with the axial suction side of the pump, depending on the rotational position of the control disc, via coincident wall openings in the pipe section of the control disc and bottom-plate pipe stubs engaging these.