Patent ID: 7578663

Claim:
A combined pump comprising: a stator having an inner housing with a helical sidewall, the helical sidewall axially extending inside said stator; and a rotary assembly housed inside said stator housing; wherein said rotary assembly comprises: a helical rotor inside said stator housing and having an outer sidewall distant from said helical sidewall of said stator housing; and a rotodynamic impeller fixedly supported around said rotor, said rotodynamic impeller radially projecting from said rotor without contacting said helical sidewall of said stator housing; whereby said rotary assembly and said helical sidewall of said stator together define cavities progressing from an intake end of the pump to a delivery end of the pump, and whereby a pressurized fluid layer is formed in a space between said rotary assembly and said helical sidewall of said stator housing and is adapted to transmit pressures between said cavities and to dissipate leakage energy so as to ensure improved pumping efficiency.