We study the pressure drop and flow regimes for large spheres with respect to the diameter of the pipe (5, 10 and 15%) by differential pressure measurements and visualizations. Two densities are used. The losses are smaller for large grain sizes, and density has a strong effect on the transition point between regimes with a stationary bed flow and dispersed flows. Models based on the Froude number are tested. Finally, we study mixtures of size and / or density. We are also interested in plugging and unplugging transients