A simulation is presented of the flow and pumping behavior of an intermeshing counter-rotating twin screw extruder. The problem of incorporating the positive displacement characteristics of moving machine parts in a cylindrical coordinate Flow Analysis Network (FAN) analysis is presented. Screw pumping characteristic curves were determined for various elements of the Leistritz GG modular counter-rotating twin screw extruder for a Newtonian fluid. We discuss the analysis of composite modular counter-rotating twin screw extruders using these screw pumping characteristics.