Abstract: An MWE compressor comprising a housing defining an inlet and an outlet, and an impeller wheel rotatably mounted in the housing such that on rotation of the wheel gas within the inlet is moved to the outlet. The housing has an inner wall defining a surface located in close proximity to radially outer edges of vanes supported by the wheel. The inlet is defined by a first tubular portion an inner surface of which is an extension of the said surface of the inner wall of the housing, a second tubular portion located radially outside the first portion to define an annular passage between the first and second portions, a wall extending across the annular passage between the first and second portions, and a conical wall located upstream of the first portion and extending in the radially outwards and upstream directions from adjacent the upstream end of the first portion to the upstream end of the second portion.