Automated fabrication of concrete elements requires precise control of outgoing volume flow. Since measurements of the volume flow or the total extruded volume are challenging during production, a feedforward control is required, which in turn necessitates a model of the dynamics at hand. In this paper, a concrete conveyance system with two pumps is considered. These are mounted at the inlet and outlet of the hose, respectively. Based on previous work, a dynamical model with concentrated parameters is derived, which is motivated on the general distributed dynamics of two-phase flow. The model is validated by experiments, with parameters calculated by a tailored estimation approach. Based thereon, a feedforward control approach is presented and tested in simulation, exploiting the approximate flatness of the system. The flat parametrization is then used for constrained, smooth setpoint transition of the volume flow with minimal transition time.