There are three basic runner system layouts typically used for a multi-cavity system. These layouts are illustrated in Figure 1 below.
Standard (herringbone) runner system
“H” bridge (branching) runner system
Radial (star) runner system
FIGURE 1. Basic runner system layouts
Balanced vs. unbalanced 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.
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.
Runner balancing can be accomplished automatically with runner balancing analysis.
Hot runner system for different products have different Nozzle: