A Runner is a machined groove located between (and includes) the Sprue Bushing and the Gate.

    The function of a runner is to provide a passage for the material to flow from the Sprue Bushing to the Gate.

    There are many types of Runner cross sectional shapes.  Most common shapes are the Full Round, Half Round, and the Trapezoidal.  

    As the Runner branches and changes direction from the Sprue to the Gate the runner is reduced in its cross-sectional area (typically about 25%).  The portion coming from the Sprue is referred to as the Primary Runner, the next section is referred to as the Secondary Runner, and followed by the Tertiary Runner.

    The length of a runner system should be kept to a minimum.  Injection Pressure build-up due to long runner lengths can be reduced by increasing the runner diameter.  However, larger runner diameters increase cycle time due to the added volume of  material that needs to be chilled/solidified.  2

    Below the point where the bottom of the Sprue Bushing and runner meet, there is a small cold slug well, and some form of sprue puller.

Sprue Puller