Gear pump (1) for pumping liquids, of the type comprising: a stator unit (2), which is equipped with a substantially cylindrical cavity (3) and is designed to generate a magnetic field rotating on the inside of said cavity (3); a substantially tubular, cylindrical bush (4), which is keyed on the inside of the cavity (3) of the stator unit (2); and at least one pumping gear (5, 6) housed in an axially rotatable manner on the inside of the bush (4); one or more longitudinal grooves (12) being present in the zone of contact between the stator unit (2) and the bush (4), said longitudinal grooves extending in the interstitial space between the bush (4) and the stator unit (2) and being designed to conduct an adhesive inside the interstitial space between the bush (4) and the stator unit (2).

A fluid displacement apparatus includes a stator section with a rotor therein. The stator section includes a cylindrical casing, a helically-convoluted chamber section within the cylindrical casing, and a rigid sleeve within the cylindrical casing and separate from the helically-convoluted chamber section. The rigid sleeve includes a circular internal bore. The rotor is rotatably disposed within the cylindrical casing. The rotor includes a helically-lobed section disposed within the helically-convoluted chamber section, and a circular cylinder section disposed within the rigid sleeve. The circular cylinder section provides a fluid passageway between the rigid sleeve and the circular cylinder section. Side loads from the rotor are distributed along a contact line at any point of rotation of the circular cylinder section within the rigid sleeve.

The present teachings generally include a rotor assembly having a plurality of rotor sheets or layers mounted to a shaft, and methods of construction for a rotor assembly. Each rotor sheet or layer in the assembly may be provided with a central opening extending between the first and second sides through which the shaft extends. In one aspect, the rotor sheets or layers can be provided with a plurality of lobes extending away from the central opening, wherein each of the lobes can have a lobe opening extending through the thickness of the sheets or layers. In one example, the rotor sheets or layers can be rotationally stacked to form a helical rotor. In one example, the rotor sheets are formed from a pre-cured composite material and are bonded together with an adhesive.