A compressor assembly, and more in general relates to a compressor for a gas turbine providing a solution that teaches to locate within a cavity formed by the outer casing of the compressor and the inner vane carrier a separator element, or membrane, such to divide the cavity into two sub-cavities. This advantageously results in a more flexible design with respect to the positioning of the flange blow-off extractor and to the cavity sizing, as the flange position is not necessarily the boundary for the flow anymore as it would be without the separator element.