Congruent velocity distributions in parallel channel cross sections are assumed in conventional flow theories for screw pumps. That assumption leads to nonuniform pressure distributions along the oblique channel ends. These pressures should be uniform when screw-pump inlet and discharge connections do not restrict flow. A new theory for isothermal flow through channels with large aspect ratios is derived based on uniform pressures along oblique ends. End-effect correction factors for drag flow and pressure back-flow rates are given as functions of L/D and helix angle. Calculated pressure distributions, streamlines, and the end factor for pressure backflow are compared with experimental values.

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