a filter assembly for extruded polymer melts is described which comprises a filter having retained between inlet and outlet manifolds with a contact pressure that can be varied . a primary seal device between the manifold and the housing is located in a rabbet in either the housing or the manifold at the contact plane . this seal responds to pressure from the polymer melt flow by deforming and increasing the contact pressure between the manifold and the housing . thus the greater the pressure at which the melt is extruded , the tighter is the seal .