In this investigation the flow of a thermoplastic polymer melt through the non-return valve of an injection molding machine was simulated using the Finite Element Method (FEM). Only the dosing step of the injection molding cycle was considered. The simulated results showed that as expected an axial pressure flow is induced within the non-return valve. The corresponding pressure differential can be used to determine a simulated pressure at the entrance to the non-return valve. An analysis of the change in the relevant material parameters, in this case the parameters for the Bird-Carreau-Yasuda viscosity model; η_0, λ and n, showed that a change in the zero viscosity η_0 effects the pressure differential but not the velocities or shear rates whereas λ effects the shear rates without having a significant effect on the pressure and the velocities provided that shear thinning (the extent of which λ directly effects) is present. If shear thinning is present n has a similar effect on the simulated results as λ. Fechter, R. H., Liang, L., Fischer, M. and Kühnert, I. SPE ANTEC: Detroit, Michigan, USA (2019)