Exemplary embodiments are directed to a rotary selector valve that includes a valve body that includes a rotor and a stator. The stator includes a first port for flow of a first flow material and a second port for flow of a second flow material. The rotor includes a groove for flow of at least one of the first flow material and the second flow material. The rotor includes a vent groove disposed between the first port and the second port for venting at least a portion of at least one of the first flow material and the second flow material to an exterior of the valve body. Exemplary methods of operating a rotary selector valve and CO2-based chromatography flow systems including a rotary selector valve are also provided.