A pump unit includes a pump housing with an inlet and an outlet and a rotor arranged in the pump housing. The pump unit is designed for a non-contact magnetic levitation of the rotor and for a non-contact magnetic drive of the rotor by the stator. The vanes of the rotor are arranged around a central inlet area of the rotor, and the rotor includes a relief opening for generating a recirculation flow which is directed from a back side of the rotor facing away from the inlet in the direction of the central inlet area of the rotor, and a separating element arranged in the central inlet area, which redirects the recirculation flow in a radial direction perpendicular to the axial direction. The, the separating element and the relief opening of the rotor are a one-piece unit.

A propeller having a plurality of blades extending radially outward from a hub, the blades forming a loop. Each loop can have an intake portion, an exhaust portion and a tip portion extending radially outward from the hub and a gap between the intake root and the exhaust root.

A liquid supply device that reduces particle generation includes a pump configured to supply a liquid to a nozzle within a wafer processing chamber, a controller configured to control the pump, and a main power source configured to supply electrical power to the pump. The pump includes a stator, a coil surrounding the stator, a case having an internal space, and an impeller within the case internal space. The impeller is rotated by a magnetic force generated by the stator and the coil. When the electrical power is shut off from the main power source to the coil, the controller is configured to reduce a rotational speed of the impeller and stop the pump.