Abstract: The present invention provides a compressor comprising a housing 1 defining an air inlet passage 2 and a volute duct. A rotary impeller 6 is located within the housing 1 between the inlet passage 2 and the volute duct. A sleeve 3 is mounted axially in the inlet passage 2 and divides the inlet passage into a radially outer portion 4 and a radially inner portion 5. A plurality of inlet guide vanes 8 are positioned in the radially outer portion 4 and impart a rotary component of movement pre-swirl) to air passing through the inlet passage 2. A fluid cut-off valve 9 is positioned in the radially inner portion 5 and for selectively preventing fluid flow therethrough and diverting all of the air through the radially outer portion 4 of the inlet passage 2 at low mass flow rates.