A device comprising: a housing having an internal surface defining an internal cavity , the housing being configured to transfer hydraulic fluid between the internal cavity and an external reservoir, and the internal cavity having a substantially circular cross sectional curvature; a rotor coupled to the housing, the rotor including a first slot having a substantially circular curvature, and the rotor being configured to rotate within the housing in response to an application of a rotational force; a first vane disk partially disposed within the first slot of the rotor, the first vane disk having a substantially circular external geometry, the first vane disk being mechanically coupled to the rotor via the first slot, and the first vane disk being configured to form a first seal with the internal surface of the housing; and a first separator device included in the internal cavity of the housing, the first separator device being configured to form a second seal with the internal surface of the housing and a third seal with an external surface of the rotor; and characterised in that the first slot is configured and precisely contoured to the geometry of the first vane disk such that, in the manufacturing process, about half the first vane disk is inserted into the first slot of the rotor and held in place by the mechanical coupling between the first vane disk and the rotor provided by the mating of the first vane disk with the rotor achieved by the precise fit between the first slot and the first vane disk, wherein no additional locks or mechanical coupling devices couple the first vane disk to the rotor. a housing having an internal surface defining an internal cavity , the housing being configured to transfer hydraulic fluid between the internal cavity and an external reservoir, and the internal cavity having a substantially circular cross sectional curvature; a rotor coupled to the housing, the rotor including a first slot having a substantially circular curvature, and the rotor being configured to rotate within the housing in response to an application of a rotational force; a first vane disk partially disposed within the first slot of the rotor, the first vane disk having a substantially circular external geometry, the first vane disk being mechanically coupled to the rotor via the first slot, and the first vane disk being configured to form a first seal with the internal surface of the housing; and a first separator device included in the internal cavity of the housing, the first separator device being configured to form a second seal with the internal surface of the housing and a third seal with an external surface of the rotor; and characterised in that the first slot is configured and precisely contoured to the geometry of the first vane disk such that, in the manufacturing process, about half the first vane disk is inserted into the first slot of the rotor and held in place by the mechanical coupling between the first vane disk and the rotor provided by the mating of the first vane disk with the rotor achieved by the precise fit between the first slot and the first vane disk, wherein no additional locks or mechanical coupling devices couple the first vane disk to the rotor. <EOS>