Abstract: A vane-type rotary compressor comprises a cylinder which receives an axially mounted rotor. A shaft end connected to the rotor carries a groove which registers with holes provided in an axially slidable ring. The ring slides axially within a central cavity in an end plate fixed to the cylinder. The end plates carries radial passages for communication with the holes in the ring. One hole for expelling gas from chambers defined by radially movable vanes in the rotor, always communicates with an arc-shaped groove on the plate through one of the holes in the ring. This is despite the axial position of the ring. Two other holes are provided in the ring near opposite axial ends of the ring for varying amounts of overlap with a discharge an an unloading passage. In this way with the ring at one axial end of its stroke, all of the gas is discharged while at the opposite end of the stroke all of the gas is supplied to the unloading passage.