An open system is one where the DEF container is not sealed from external contaminants during one or more usage phases, i.e. filling, transporting, dispensing or disposal. A typical open system involves installing a drum pump with a "stinger" or "stick" type dip-tube at the end use site.
PRO: This type of system is reusable and does not normally add cost to the container package. However, if the "stinger" (pump) is shipped with the container this solution becomes extremely expensive and is only suitable for reusable applications.
CON: This type of system typically uses an unfiltered venting path (a hole in the drum bung) which is open to atmosphere while dispensing providing a likely potential source of DEF contamination. also, during container change out the "stinger" must be removed which is cumbersome, messy and provides a significant opportunity for contamination of the DEF. This type of system has a high initial cost.