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The purpose of this research is the development of guiding principles and rules for the design of running systems for aluminium castings, employing both the "virtual" experiment, a computational modelling package, and the "physical" experiment, the real-time X-ray radiography study. "Diverging-Bend" geometry has an essential feature in which the flow rate of the system could achieve the maximum and the velocity of advancing flow could reduce without developing surface turbulence. In liquid aluminium, the surface tension becomes more significant compared to water during the flow transformation from supercritical to subcritical velocities. To describe the phenomenon of hydraulic jump for liquid aluminium it is necessary to include the surface tension, giving the relation pV 2 = (pxgxH) + (4T/H) where p: density, V: average velocity, g: gravitational acceleration, H: the height of the hydraulic jump, and T: surface tension. Guidelines for the designing of L-junctions are developed. Five geometries of L-junctions can be applied and assembled in the design of runners and multiple-gate system. Progressive filling along the L-junction geometry can be achieved by reducing the area of the "dead zone". In a multiple-gate system uniform distribution of flow rate through each gate into the mould cavity is achieved. Quantification of a running system is established by the measurement of coefficient of discharge Cd. The loss coefficient K for individual component of runners is also estimated.