This paper presents a comprehensive and modular model for flow rate maneuvering systems. The nonlinear system equations are derived starting from physical principles, and describe the power unit, the mechanical transmission, the butterfly valve, the load torques and the fluid flow inside the pipe. The system equations are subsequently parametrized using data from blue prints and experiments in order to perform numerical investigations. It is shown that the hydrodynamic torque plays an important role in operation, and that pipe pressure losses affect the hydrodynamic torque. Also, the effects of fluid dynamics are shown and discussed. The proposed model provides insights for the design of both actuation systems for butterfly valves and suitable control concepts.