Flexible shaft assembly for progressing cavity pump

Claim 1

In a progressing cavity, positive displacement rotary pump, including a housing, a rotary drive shaft journaled in said housing, drive means for said shaft, a generally tubular stator coaxial with said rotary shaft, and having a helically formed interior surface, and a hollow, orbital rotor received in said stator and having a helically formed exterior surface engaging said interior surface of said stator to define therewith, pumping cavities that progress axially when said rotor is simultaneously rotated and orbited within said stator, the improvement which comprises: means defining a coupling socket at the opposite end side of said hollow rotor from said drive shaft, said means including an axially extending internal seat portion of polygonal transverse cross-section that tapers inwardly toward said opposite end, a flexible coupling shaft extending through said rotor and connected at its outer end to said opposite end of said rotor and at its inner end to said rotary drive shaft, said coupling shaft having a coupling head at its outer end of polygonal, transverse cross-section that tapers inwardly toward said outward end to mate with said tapered seat in said rotor, means defining an axial bore extending through said opposite end of said rotor to said socket, means defining an axial threaded bore in said head, and a threaded fastener engaging said rotor and extending inwardly through said axial bore in said rotor and into said threaded axial bore in said head to tightly anchor said head in said socket, whereby said drive shaft turns said rotor through said coupling shaft and said coupling shaft flexes to accommodate orbital movement of said rotor during rotation thereof.