Abstract: An ink jet printer having an ink jet head unit including a head and a three way valve mounted on a bracket. The bracket is removabley mounted to the printer and allows the unit to be replaced in the field. The valve of the new unit is positioned to close off flow to the head while opening flow from the ink source outlet to a disposal outlet. Upon connection of the new unit to the system, a quantity of ink is flushed through the valve to remove impurities introduced during the connection process. The valve is then adjusted to connect flow of ink to the head while closing off the disposal outlet and thereby avoid contamination of the new head.