some times sprue bush need cooling to cut the cycle time of injection process, when diameter of sprue is large cooling in sprue bush is important. some fabrication of mold part have their own sprue bush that containing cooling pipe. like picture below
from those picture some standard part mold company have their own methods to make inner cooling at the sprue bush, we can by cutting in some part that weld together again, or by other method.
the other way to make cooling in sprue is like picture below
by those type of sprue we change the entrance and exit flow by using stopper buffle, for example like picture below
or you can make the flow straight, the other cooling method in sprue is like picture below, by using this type is easy to attach the O ring, becouse in and out flow from below side that contact with moldbase. becouse when assembling of ring to moldbase is more easy by attach the O ring in Moldbase then put the sprue bush than attach the O ring in sprue bush and assembling it together in moldbase.