A compressor comprising: a shell assembly defining a discharge chamber; a non-orbiting scroll including a first end plate and a first spiral wrap extending from the first end plate; an orbiting scroll including a second end plate and a second spiral wrap extending from the second end plate, the first and second spiral wraps meshing with each other to define a plurality of fluid pockets therebetween, the fluid pockets movable among a radially outermost position, a radially intermediate position, and a radially innermost position, the second end plate including a variable-volume-ratio port extending therethrough and selectively communicating with one of the fluid pockets at the radially intermediate position; and a variable-volume-ratio valve assembly mounted to the orbiting scroll, characterized in that: the non-orbiting scroll and the orbiting scroll are disposed within the discharge chamber, the variable-volume-ratio valve assembly includes a valve member that is movable relative to the orbiting scroll between an open position allowing communication between the variable-volume-ratio port and the discharge chamber and a closed position restricting communication between the variable-volume-ratio port and the discharge chamber, and when the valve member is in the open position, fluid flows from the variable-volume-ratio port to the discharge chamber without flowing back into any of the fluid pockets. a shell assembly defining a discharge chamber; a non-orbiting scroll including a first end plate and a first spiral wrap extending from the first end plate; an orbiting scroll including a second end plate and a second spiral wrap extending from the second end plate, the first and second spiral wraps meshing with each other to define a plurality of fluid pockets therebetween, the fluid pockets movable among a radially outermost position, a radially intermediate position, and a radially innermost position, the second end plate including a variable-volume-ratio port extending therethrough and selectively communicating with one of the fluid pockets at the radially intermediate position; and a variable-volume-ratio valve assembly mounted to the orbiting scroll, characterized in that: the non-orbiting scroll and the orbiting scroll are disposed within the discharge chamber, the variable-volume-ratio valve assembly includes a valve member that is movable relative to the orbiting scroll between an open position allowing communication between the variable-volume-ratio port and the discharge chamber and a closed position restricting communication between the variable-volume-ratio port and the discharge chamber, and when the valve member is in the open position, fluid flows from the variable-volume-ratio port to the discharge chamber without flowing back into any of the fluid pockets. the non-orbiting scroll and the orbiting scroll are disposed within the discharge chamber, the variable-volume-ratio valve assembly includes a valve member that is movable relative to the orbiting scroll between an open position allowing communication between the variable-volume-ratio port and the discharge chamber and a closed position restricting communication between the variable-volume-ratio port and the discharge chamber, and when the valve member is in the open position, fluid flows from the variable-volume-ratio port to the discharge chamber without flowing back into any of the fluid pockets.