The external gear pumps are devices used in a wide range of applications that go from the industrial field where, for example, they can be used to transfer the fluid along a productive process system, or in mobile applications and off-road vehicles. They are valuable for their simplicity, robustness, the possibility of working with a wide range of fluid viscosity and the low cost. Such a widespread usage underlines the advantage that a deeper control in the design process would lead. The deeper control just mentioned, is brought through the model presented in this thesis. More precisely, in this thesis is first described HYGESim, an external gear pump lumped parameter model developed by the MAHA Fluid Power Research Center.