The L-shaped junctions in running and gating systems used in aluminum gravity casting have been investigated. Using computational modeling, a guideline for constructing two geometries of L-junctions was developed. The sequential filling profile of liquid metal along L-junction was confirmed by real-time X-ray video of an aluminum alloy sand casting. The change of flow direction through L-junctions can yield a high coefficient of discharge Cd, without entrapping detrimental oxide film defects because of the smooth flow, minimizing surface turbulence. A short “clear-up” time, the duration of filling a component, of L-shaped junction is also achieved. For the necessary of future application of this junction, its dimensionless equivalent lengths (L_E/D) and loss coefficient K were estimated. The main aim of this work was to eliminate the trial and error approach as designing a multiple-gate system. From the guideline of L-junction, the two junctions can be assembled into a complex multiple-gate runner system. In this novel design of multiple-gate system, uniform distribution of flow through each gate into a mould cavity has been demonstrated. A high Cd value was also predicted.