the present invention provides a barrel venting system for use on an extruder . gases that are generated during plasticizing are drawn by vacuum through a filter to remove plastic particles before the gas is exhausted to the atmosphere . to enable cleaning of the filter without interrupting extruder operation , a shuttle valve is provided to allow rapid switching of the gas flow to a second filter . the valve itself includes two disc shaped elements with ports that align in two positions to enable flow to either the first or second filter , as desired .