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Basic layouts
There are three basic runner system layouts typically used for a multi-cavity system.
These layouts are illustrated in Figure 1 below.
l   Standard (herringbone) runner system
l   “H” bridge (branching) runner system
l   Radial (star) runner system

FIGURE 1. Basic runner system layouts

Balanced vs. unbalanced layouts
Balanced layouts
The “H” (branching) and radial (star) systems are considered to be naturally balanced. The naturally
balanced runner provides equal distance and runner size from the sprue to all the cavities, so that
each cavity fills under the same conditions.
Unbalanced layouts
Although the herringbone is naturally unbalanced, it can accommodate more cavities than its
naturally balanced counterparts, with minimum runner volume and less tooling cost. An unbalanced
runner system can be artificially balanced by changing the diameter and the length of the runner.
Automatic balancing
Runner System Layout
Runner balancing can be accomplished automatically with C-MOLD runner balancing analysis.