Abstract: A liquid ring pump comprising a housing, a substantially oval chamber within said housing, and a hub supporting a plurality of radially disposed vanes adapted to rotate within said chamber, said pump being such that the interstices between said individual vanes are partially blocked by a blocking mass which rotates with said vanes and which raises the stall pressure ratio of said pump to increase its pumping efficiency. The blocking mass is additional to the hub and in the case where the liquid ring pump also includes a gas/liquid mixture inlet port and a gas discharge port arranged on opposite sides of said pump, then the blocking mass forms a weir which gives the additional advantage that it acts to prevent the direct axial migration of liquid from said inlet port to said gas discharge port, thus enabling said pump to easily separate said gas liquid mixture into separate gas and liquid phases.