A polymer filtration apparatus for sealing a slide plate translatable across a bore of an extrusion or mold machine, includes an annular seal having a sealing surface which is biased against the slide plate by a spring mechanism. The annular seal has a thrust surface which is angled relative to the sealing surface and the thrust surface is located at an opposite axial end of the annular seal from the sealing surface. The spring mechanism can be a single spring with overlapping tangs or a multiple spring assembly in overlapping relationship, with or without tangs, to form a continuous barrier. The spring assembly is used to exert a radial force against the thrust surface of the annular seal to bias the seal in an axial direction against the downstream slide plate. In operation, pressurized polymer melt in the extrusion bore further biases the spring against the annular seal which is then transferred to the seal and the slide plate.