Abstract: A pump including at least three rotors each being provided with a generally helical screw thread, the rotors being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the rotors or where one of the rotors has a larger outer diameter than the other rotors the outer diameter of the larger diameter rotor.

Abstract: A pump including a power rotor and an idler rotor, the rotors each being provided with a generally helical screw thread and being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, the power rotor being connected to a driving means operation of which causes rotation of the power rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the power rotor, the depth of the threads is less than or equal to 0.2 times the outer diameter of the power rotor, and the root diameter of the idler rotor is less than 0.31 times the outer diameter of the power rotor.

Abstract: A motor driven pump comprises a motor stator (30), a motor rotor (10) operable to rotate around the outside of the stator (30) and a pump mechanism (40, 50) driven by the motor rotor (10) and disposed at least partly inside the motor stator (30).