Flow forces acting on spool valves arise due to the momentum exchange between fluid and spool when the fluid passes through a valve. In a steady-state, they usually act in the valve-closing direction, and therefore have to be overcome by the actuation system. In this thesis, steady-state flow forces acting on directional control spool valves are evaluated. Different spool and sleeve geometries of non-commercial 2/2-way spool valves are investigated using measurements, simulations and theory in two flow directions with the mineral oil HLP 46. The flow-force measurements are used to validate a CFD simulation of the analyzed valves. Furthermore, a dimensional analysis is applied for scaling the entire valve geometry and fluid properties. An analytical model for the flow-force calculation is derived and validated for the non-commercial valves. It is based on the law of momentum conservation and allows for both the influx and efflux of the fluid. Flow angles and flow velocities necessary for the flow-force calculation are determined using CFD simulations as functions of several parameters depending on the spool geometry. For this purpose, the approach Design and Analysis of Simulation Experiments is utilized in the software ANSYS Workbench. The results show that the flow forces of the non-commercial valves are accurately evaluated using the novel analytical model. In addition to the non-commercial valves, three commercial 4/3-way proportional directional-control valves of the nominal size 10 are experimentally investigated regarding their flow-force and flow-rate characteristics. The measurements are used for verification of the flow-force analytical model. It is proven that the analytical model delivers good results for estimating flow forces of such valves.