Abstract: A pump for pumping a gas, the pump comprising: a rotor and a stator; the rotor comprising at least one liquid opening configured for fluid communication with a liquid source. The liquid opening is configured such that in response to a driving force a stream of liquid is output from the opening, the stream of liquid forming a liquid blade between the rotor and the stator, gas confined by the stator, the rotor and the liquid blade being driven through the pump along a pumping channel from a gas inlet towards a gas outlet in response to relative rotational motion of the rotor and the stator. A cross sectional area of the pumping channel is configured to increase from the gas inlet to the gas outlet.

Abstract: A screw pump comprises a pair of rotors (92, 94) each carrying an external screw thread (96, 98), the pair of rotors being rotatably mounted in a stator (72) and arranged such that, in operation, the screw threads of the rotors intermesh as the rotors rotate in opposing directions. Means (100, 102) are provided for actively controlling the axial position of the rotors within the stator during use of the pump.