A rotary fluid-displacement assembly having a housing and a rotor positioned within an internal cavity of the housing. The rotor being configured to rotate about a rotor axis of rotation eccentric to a housing longitudinal axis. A gate is also provided that is slidably mounted therewith the rotor and movable axially about and between a first position, in which a distal end of the gate is positioned at a first distance from the peripheral surface of the rotor, and a second position, in which the distal end of the gate is positioned at a second distance from the peripheral surface of the rotor.The distal end of the gate being constrained to be spaced proximate from the inner wall surface of the housing as the rotor rotates about the rotor axis of rotation.