Progressive cavity pump

Claim 1

A progressive cavity pump comprising a stator member and a rotor member disposed within the stator member, one of said members being formed of resilient, rubber-like material and the other of a rigid, metal material, said rotor member being of helical formation having a circular shape constant in diameter at any transverse cross-section, and thereby providing a single-start thread of preselected direction and length, the ratio of the pitch of the rotor to the diameter of the circular shape of the rotor being no greater than approximately 1:1, said stator member having an internal cavity in the form of a two-start helical thread of the same direction and twice the pitch length of the rotor member, said cavity in transverse cross section having an oblong outline defined by a pair of spaced concave semi-circular ends and sides joining the semi-circular ends, the semi-circular ends having a diameter slightly less than the diameter of the circular shape of the cross section of the rotor for establishing an interference fit between said resilient and rigid members and thereby providing areas of substantially constant contact pressure between the rotor and semi-circular ends of the cavity in the stator, said pair of sides having an inward curvature whereby the distance between said pair of sides is sufficiently less than the diameter of said semi-circular ends to establish an increased interference and thereby provide an increased area of contact between the rotor and the inward curved sides of the cavity of the stator and wherein said contact area has pressure contact greater in magnitude than said contact pressure between the rotor and the semi-circular ends, the inward curvatures of the sides being arcs of circles having centers outside of the cavity on opposite sides thereof, the radii of the arcs forming the inward curvatures being slightly less in length than the diameter of the semi-circular ends.