This is the first part of a trilogy that reports the results of combined experimental and computational investigations of fluid flows in the active space of needle valves - the configurations of which are characterised by rounded needle tip or exit channel entrance or both. Interest in these rounded shapes arose recently due to planned needle valve applications for very high temperatures and possibility of erosion by aggressive hot fluids, endangering the valve by rapid deterioration. This Part I discusses mainly the geometry of the problem and configurations of the models used in the tests reported in subsequent Parts I and II. (C) 2016 Elsevier B.V. All rights reserved.