Abstract: A resilient compressor ball is compressed to urge an axially-movable circular knife-edge onto one end of a cylindrical filter element to form a seal therewith and to urge the filter element onto a fixed circular knife-edge having a fluid outlet opening therewithin to form a seal therewith. The movable knife-edge is concentrically formed on an axially-slidable tubular compressor element which confines the compressor ball within a hollow nut portion of a cap which is screwed onto a cylindrical shell having a base from which the fixed knife-edge extends in axial alignment with the movable knife-edge. When the cap is screwed onto the shell, the compression of the ball urges the movable knife edge against one end of the filter and the other end of the filter against the fixed knife-edge so as to seal the ends of the filter element and thus the seals formed at the knife-edges, while accommodating variances in the overall length of the filter element from its nominal length.