Simulations are an important tool for investigation of transients and dynamic behaviour of systems. For hydraulic systems, the characteristics of hydraulic machinery is important for the simulation results and their reliability. If experimental results are available, they can be used by creating so-called Suter curves (Wylie and Streeter, 1983). If no results are available, a model must be used. For hydraulic turbines, the two most important properties to model correctly are the torque acting on the machine from the moving fluid and the head the machine requires to be subjected to for a certain flow to be maintained at a certain rotational speed and guide vane opening. Traditionally, both the torque and the head has been modelled using the Euler equation (Nielsen, 2015, Nielsen and Storli, 2014, Nielsen, 1996, Giosio et al., 2017), but there are issues which should be addressed related to the use of this equation as a basis for simulation models for hydraulic turbines. The purpose of this paper is to provide insight and un-ambiguous derivation of equations describing models for torque and head for a hydraulic turbine, in this case a Francis turbine, and to point out and discuss problems concerning the validity of the models.