The runner system should be designed so that all of the parts finish filling at the same time. To do this it might be necessary to balance the runner system.
Before you design the runners for a family injection mold, analyze each part on its own. Once you know that each cavity will fill, then you can design the runner system to create balanced fill paths in each cavity. If the runners are not balanced, molding problems such as hesitation, underflow and overpacking may occur.From Website
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