Abstract: A rotary ball valve assembly for a rotary ball valve comprises a rotary closure element and an impedance assembly. The closure element is rotatable about a rotational axis, and has a through-bore defining a flow inlet and a flow outlet. The impedance assembly is positioned, at least in part, within the bore of the closure element. The impedance assembly includes a plurality of flow passages therethrough. An inlet and/or outlet of two or more of the flow passages is elongate and arcuate so that, in use, as the closure element rotates, the arcuate elongate inlet and/or outlet of each flow passage which is exposed is fully or substantially fully opened.