Flow force acting on a valve disc plays an important role in the overall performance of pressure safety valves (PSVs). To quantify the disc force, Computational Fluid Dynamics (CFD) methods have been widely implemented. In this paper, the capability of CFD models, and the identification of the most suitable turbulence models' geometry modelling and mesh requirements have been assessed to establish the accuracy of CFD models for disc force prediction. For validation purposes, a PSV disc force measuring rig is designed and constructed, by which the steady state flow forces exerted on the valve disc at different valve openings can be obtained. The CFD model assessment is achieved by comparing the simulation results to that obtained from experiments; this is achieved in two stages. Stage 1 investigates the use of RANS based turbulence models where 2-D simulations are performed with five turbulence models. The results indicate that a variety of force results are produced by different turbulence models, among which the SST k-? was found to have the best performance. Stage two investigates meshing and the use of symmetry and geometry simplifications; 2-D, 1/8 3-D and 1/2 3-D mesh models are examined. The results indicate that the 1/8 3-D mesh model is the optimal choice, owing to its higher accuracy and reasonable grid scale. The studies performed in this paper extend the knowledge of compressible flow force prediction, and is expected to facilitate the understanding, design or optimization process of PSVs.