Systems, methods, and devices are configured to implement hydraulic actuators. Devices may include a housing having an internal surface defining an internal cavity that may have a substantially circular cross sectional curvature. The devices may include a rotor that includes a first slot having a substantially circular curvature. The devices may include a first vane disk partially disposed within the first slot of the rotor, where the first vane disk has a substantially circular external geometry. The first vane disk may be mechanically coupled to the rotor via the first slot, and the first vane disk may be configured to form a first seal with the internal surface of the housing. The devices may include a first separator device that may be configured to form a second seal with the internal surface of the housing and a third seal with an external surface of the rotor.